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Geology 101 Lab Manual Quartz Crystals Quartz is a common component of all rock types. We will explore rocks and minerals in weeks 2 through 5. Geology Department Western Washington University Table of Contents Table of Contents 1 Acknowledgments2 Introduction and Important Information 3 How to Use Google Earth 7 Academic Integrity 8 Lab #1: Plate Tectonics 11 Introduction to Rock Cycle 27 Lab #2: Igneous Rocks 31 Lab #3: Sedimentary Rocks and Depositional Environments 47 Lab #4: Metamorphic Rocks 67 Lab #5: Rock Quiz and Campus Field Trip 79 Lab #6: Streams, Coastlines & Groundwater 85 Lab #7: Geologic Hazards in Whatcom County 97 Lab #8: Geology of Washington 107 Lab #9: Comprehensive Lab Quiz Study Guide 117 Rocks Identification Charts 119 Mineral Identification Tables 121 1 Acknowledgments This lab manual is an evolving project that began Fall Quarter, 2000, written and compiled by faculty and graduate students of the Geology Department at Western Washington University. Primary contributors are Terri Plake, Geology 101 Instructors, Erik Bilderback, Chris Houck, Dave Tucker, Michelle Malone and all Geology Teaching Assistants. Others who have provided significantly to this project are George Mustoe, Scott and Marca Babcock, Dan Bunk, Katie Callahan, Andrew Greene, Pete Stelling, Gerry Greisel, Casey Hannell, and Paul Thomas. Scott Linneman provided ideas and inspiration. Portions of several labs were modified from the Geology Lab Manual of the Department of Geology and Geophysics, University of Minnesota, and a geology lab manual from Lewis-Clark State College. The plate tectonics lab was modified from an exercise written by Dale S. Sawyer, Rice University. Thank you to George Mustoe who has provided advice and technical support over many years. In addition, we have benefited greatly from comments and suggestions made by the teaching assistants and students of the Geology 101 labs. We thank you! By no means is this manual finished. If you have any comments or suggestions, we would appreciate hearing from you. Geology Department Western Washington University August, 2001 Revised continuously through September, 2013 Figure 1. Gneiss with granite and pegmatite dikes cutting across it, Laxford, England. Image source: http://www.earth.ox.ac.uk. 2 Introduction The purpose of Geology 101 Lab is to give you hands-on practice in the application of geologic principles. Geology 101 lab gives you the opportunity to develop skills of observation, and to see the Earth in new ways. In this lab you will take a closer look at what the Earth is made of, what processes form our landscapes, what changes are taking place during your life time, what changes could take place in the future. You will learn to make reasonable interpretations from your observations. This lab manual will start with a big picture of the Earth and then zoom in. As a class, we will: Figure 2. A student climbing to get a better look at the gravels in Alaska.Image source: Pete Stelling. • Examine plate tectonics and Earth’s features. Plate tectonics provides a framework in which to study and understand the interrelationship of all Earth Systems. • Examine the materials of which our planet is made. Each rock has a story to tell that you will learn to read. • Examine landscapes produced and modified by physical processes of erosion and deposition in river, glacial, shoreline systems. These landscapes are represented on topographic maps. Map reading skills will enhance your life in many ways, having many practical applications, from land ownership, water well locations, and enjoyment of outdoor activities. You should supplement this lab manual with your textbook where you can find glossy colored photographs and diagrams. We recommend that you bring your textbook to each lab session to use as a handy reference. Each lab exercise follows this format: Warm-Up Quiz: This is done on the Canvas page for the geology lab (not on your lecture class Canvas page). This must be completed by 11:55 PM the night before your lab. The quiz covers material from the upcoming lab, as well as short review from the previous lab, and is designed to prepare you for the lab work to be completed during class. ConcepTest: A ConcepTest will be given at the beginning of each lab period. These assessments are not graded, but may be used to determine attendance. The ConcepTests are challenging and designed to determine what you already know about the subjects we’ll be dicussing in lab. Objectives: A list of concepts and skills to learn and master. Materials: What you will need to bring to lab. Background information: Information necessary to complete the lab. Lab Activities: Hands-on activities and questions designed to help you to practice geology (require a TA check). Homework: To be turned in at the beginning of next lab. Figure 3. A sample of fluorite, a mineral. Image source: Rob Lavinsky, www.irocks. com. 3 Tips for Success • Organize this lab manual and your lab notes in a 3-ring binder. • Prepare before you come to lab. You need to come to lab knowing what you are going to do. You will finish the In-Class activities during the lab session if you take the time to figure out what you are going to do in lab. • Expect to spend time outside of lab time to complete the activities. The better prepared you are before lab, the more you can accomplish within the lab period. The labs are designed so that a well-prepared student should be able to finish most activities during lab, with only one or two Homework problems to finish outside of lab. Figure 4. A cutaway view of the Earth, exposing the internal • Read your lab manual and complete the pre lab structure. Image source: http://www.gkbasic.com. worksheet. • Refer often to your lecture textbook, it contains useful colored pictures and excellent diagrams. • Mastering new skills (e.g. identifying rocks or reading topographic maps) takes practice - Like learning to ride a bike, you may skin your knees a few time, but then once learned, you don't forget. • You are encouraged to work in groups. However, you are required to turn in your own work, as you will be graded for individual work. • Form study groups with your friends. • If your eyes are open, you will begin to see geology every where you go. 4 Figure 5. A cartoon diagram depicting the rock cycle, an essential concept in geology. Image source: http://www.geolsoc.org.uk. The Process of Science Geology 101 strives to teach you the process of science. There are many ways in which science is practiced, and this lab will explore many of these throughout the quarter. Notice that every week will be doing science, but not every lab will include an experiment, or even a hypothesis to test. Description, experimentation, creating models of nature, and comparisons are all valid ways of gathering new scientific data. What you do with the data is the most important part. Before each lab of the quarter: • Please read through each lab completely in the lab manual (including maps and questions). • Complete the online Warm-Up Quiz before coming to class. Warm-up quizzes are based on the material learned in the previous week’s lab and the information in the upcoming lab. Warm-up quizzes can be found in the Modules section of the Canvas web page for the geology lab course. Each quiz is listed under the corresponding lab. Access the Canvas site by: - Go to www.wwu.edu (WWU homepage). - Under the Technology heading, go to the My Western link. - Log in using your universal User Name and Password. If you do not have a User Name and Password set up yet, go to the ATUS office on the first floor of Haggard Hall (use the entrance by the fountain in Red Square, not the library entrance). - To access Canvas, click on the Canvas link (located on the top bar of the page, next to Web4U). - All of your Canvas courses should be listed on the Canvas page. This course is listed as Geology 101 Lab (make sure you know which is your lab page and which is your lecture page). Figure 6. A Laguna, CA neighborhood after a landslide. Where do you want to build your house? 5 Lab Activities A important note about the time required to complete lab activities: Lab activities have been divided into In-Class and Homework sections. The In-Class activities use materials that are only available in class, and your answers to these sections will be graded by your TA before you leave the lab room. The Homework activities are intended for you to complete after you have finished the In-Class activities - you are welcome to work on them in lab if you still have time. Homework will include short answer questions that are based on material from your In-Class activities, textbook, lecture, lab manual, and/or online resources. There are several labs that include Google Earth activities. Google Earth is available in all ATUS computer labs on campus, and is free to download if you’d like to work on your own computer (http://www.google.com/earth/ index.html). If you are new to Google Earth, refer to the next page for instructions. Don’t be surprised if you need to come back to the lab to complete a lab exercise. Some labs will take you longer than others. If you pre-read every lab, you will be more likely to complete the lab during the 2 hour lab period. Figure 7. An image of the May 18, 1980 Mount St. Helens eruption. Image source: Rob Krimmel, www.usgs.gov. 6 How to Use Google Earth There will be several labs that include questions based on using Google Earth. This is a Virtual Globe program that installed on all ATUS computers on campus and is free to download at http://www.google.com/ earth/index.html. If you are unfamiliar with Google Earth, Google provides several online tutorials explaining how to navigate and use various tools in Google Earth (for the full series of beginner tutorials, see http://www. google.com/earth/learn/beginner.html). Below is a screen shot that highlights several important elements of Google Earth that you’ll be asked to use in some lab questions. If you have questions, ask your TA or consult the Google Earth tutorials Tools Menu: where the options menu is located. Layers Panel: also include geographic web layers. Places Panel: where downloaded placemarks will appear. Scale Bar Ruler Tool Latitude/Longitude/Elevation Navigation Tools Eye (Camera) Elevation 7 Academic Integrity http://www.wwu.edu/integrity Integrity is a core value at Western, and is an essential component of being a Western student, staff or faculty member. Academic integrity is more than not cheating, and it is certainly not limited to plagiarism, as is often misunderstood. Integrity is choosing the honorable option because it is for self-betterment, not because you are afraid of getting caught. A liberal education requires you to expand your mind and broaden your understanding of the world beyond a single professional goal. Here at WWU students are encouraged to explore a variety of disciplines. In the words of Dr. Charles Sylvester (WWU PEHR Dept.), “a liberal education will help you connect seemingly disparate disciplines, and find connections between arts, sciences, humanities, and skills.” What does this mean for this course? Even if you do not intend to be a geologist, you can benefit from learning how the Earth formed, how it works, and how humans interact with and affect it. Practicing integrity means challenging yourself, striving for excellence, taking risks, learning from your mistakes, doing your own work, and giving credit whenever you use the work of others. Completing the course activities on your own is the best way to expand your knowledge and understanding of the world. If you have questions about academic integrity regarding yourself or your classmates, please talk to your TA or professor. Additional information on academic integrity can be found on WWU’s Integrity Webpage: www.wwu.edu/ integrity. This webpage provides all the information you need, including the importance of integrity, how to promote it, as well as types of academic dishonesty and how to avoid them. It also includes WWU’s policy and procedures on academic honesty (appendix D of the WWU Catalog). 8 Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Each week we will begin lab by answering questions on key concepts from this week’s reading and the previous week’s lab. These questions are not graded, but will be used as attendance. Once you complete the lab, answer the questions on the back page of the ConcepTest and compare your initial thoughts to what you have learned since. Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Lab 1: Plate Tectonics Lab #1: Plate Tectonics The purpose of today’s lab is to investigate the nature of plate boundaries using scientific data that are compiled on various types of maps. The maps plot the locations of volcanoes, earthquakes, ages of the sea floor, and topographic features (mountain chains, trenches, island chains, etc.). The plotted data displays patterns and trends that can be used to determine the locations and types of plate boundaries. Objectives 1) Learn methods of scientific inquiry, how to “do” science. 2) Look at maps that show various types of scientific data, locations of volcanoes, earthquakes, topography, and age of oceanic crust. Look for patterns in the plotted data. 3) Use the observations to make reasonable interpretations about plate boundaries and the interactions between plates. 4) Present your findings to a group of your peers and then compile your findings to make interpretations about plate boundaries. 5) Work in groups to answer questions about the Earth and global plate tectonics. Materials Pencil (no pens) Colored Pencils TestbookRuler Calculator In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Plate boundary location Activity 2: Geologic profession maps Activity 3: Characterizing boundary types Homework Activities (due the beginning of next lab) Activities on pages 17-20 Plate Tectonics The suggestion that the positions of the continents have shifted through time is a relatively old idea that dates to the first maps of the New World’s coastline. Early naturalists quickly noted the jigsaw fit between the eastern coastline of the Americas and the western coastlines of Eurasia and Africa. The idea or hypothesis that the continents have moved was eventually called continental drift. In contrast, plate tectonics is a more recent theory that describes how the continents have moved. The plate tectonics theory is one of the most important and far-reaching theories in geology. It is based on an investigation of the sea floor using technology that was not available until the 1960’s to 1970’s. The basic concept of plate tectonics is that the Earth’s rigid lithosphere is broken into about a dozen large and other small plates. The plates move relative to one another. A critical aspect of plate tectonic theory is the recognition that the continents do not shift as isolated landmasses, but that most plates are made of both continental and oceanic portions that move as a single unit. The interaction of these plates with one another is largely limited to their edges, called plate boundaries. Plate boundaries are the most active areas of the Earth’s surface. The majority of the Earth’s volcanoes, earthquakes, and regions of mountain building occur at or near plate boundaries. Plate boundaries fall into three major categories that depend on the relative motion of the adjacent plates: Divergent (move apart) Convergent (move together) Transform (slide sideways) 11 Lab 1: Plate Tectonics In-Class Activities Activity 1: Tectonics Research Group Assemble into groups of four. 1. First, get to know your colleagues. Introduce yourselves and say something about: • Your major or intended major • Why you are taking geology • Where you are from and where you live now • Share one thing that you are good at 2. Each member of your group picks a location. Choose from: • Japan • Mid-Atlantic Ridge • Northern India • San Andreas Fault Activity 2: Find Your Location You will become the expert about your location. When you return to your group, you will teach your group about your location data patterns, and what the data tells you about the nature of your plate boundary. 1. First examine the data patterns shown on each map in a global context, then concentrate on the plate boundaries listed on the chart. See hints on the bottom of this page for ideas about what to look for specifically for each map. With the patterns of data you observe, complete the chart on pg. 14 in pencil. The first plate boundary type has been completed as an example. Hint: To understand what your map says, look for patterns (especially for symmetry, asymmetry, and completeness) in the data. You must look carefully to see details. Make a list of your observations on your specialty map as you discuss them. • Seismology (earthquakes) − Determine the earthquakes’ epicenter depth: ∙ Is the epicenter shallow? Intermediate? Deep? More than one depth? ∙ Do you see any patterns? • Volcanology − Look at the geographic distribution of volcanoes, as well as their relation to plate boundaries. − Note that some volcanic chains occur on continents, some on oceanic islands, and some in ocean basins. − Are the volcanoes oriented parallel or perpendicular to adjacent plates? • Geography − Note areas of high elevation vs. low elevation. − Which are higher elevation, continental land masses or oceanic basins? Be sure to use the scale. • Geochronology (geologic ages) − What do the colors represent on this map? − What is the age distribution of oceanic crust? − Relative to the continents, where is the oldest oceanic crust? What is the relationship between oceanic crust age and boundary type? ∙ If there is no correlation between age and boundary type, be sure to state “no correlation.” Tip: A black and white copy of each map is included at the end of this lab. Be sure to review each map and the above hints for the final exam. 12 Activity 3: Reassemble Tectonics Research Groups Lab 1: Plate Tectonics 1. Discuss the findings from each locality. Go to the appropriate specialty map during the discussion. Determine how each specialty data can help distinguish between different types of plate boundaries based on the patterns observed. Step 1: Complete the chart on pg. 14 in pencil with your group members’ observations. Step 2: Come up with a hypothesis about the appropriate plate boundary type for each group of boundaries based on you observations and discussion. Fill in the boundary type names (divergent, transform or convergent) in the appropriate blanks on your chart. Step 3: Go to the Plate Boundary Map on pg. 15, use the appropriate symbols to show relative motions along the five plate boundaries listed on the chart (it is not necessary to label all the plate boundaries on the map). 13 Data: elevation in meters Associated geographic features (trench, mountain chain, island chain) and their locations Deep ocean (trench) on plate boundary, high mountains on continent inland of plate boundary GEOGRAPHY TA CHECK _____________ San Andreas Fault in California Mid-Atlantic ridge Continentalcontinental Northern India Oceanic-oceanic Japan Oceanic-Continental (example: west coast of S. Am.) 14 LOCATIONS Data: volcanoes above water Are volcanoes present in each of the boundaries? Where? Describe. Volcanoes form a northsouth chain east of the plate boundary + a few scattered on oceanic plate VOLCANOLOGY Data: Earthquake hypocenters Is there a pattern to earthquake locations? Depth? Describe. EQ’s go from shallow depth on west edge of SA plate, get deeper further inland (to east) SEISMOLOGY GEOCHRONOLOGY Why is there no oceanic crust older than 180 million Years? Youngest sea floor on west edge of Nazca Plate, oldest near plate boundary with SA plate Data: Rock ages in Millions of years Are there patterns to the relative ages of crust? Describe. Step 1: Analyze the data from your location from each map (complete using specialty hint on pg. 12, then teach your group members about your location when you regroup) (these are three variations of this type of boundary, depending on the types of interacting crust) What type of plate boundary is this? Step 2: Lab 1: Plate Tectonics Transform Divergent (with saw teeth pointing toward the overriding plate) pppppp Convergent Map Symbols TA CHECK _____________ Step 3: Go to the chart locations and draw the appropriate symbol for each boundary on this map Lab 1: Plate Tectonics 15 Lab 1: Plate Tectonics Use this page for notes, drawings, or comments that might help you answer the homework section later. 16 Lab 1: Plate Tectonics Homework Activities The rest of this lab may be completed in lab or outside of lab. You may find that working on these questions while the TA is in the room can be a big advantage. Keep in mind that some questions will require computers that are not available in the lab room. Activity 1: Plate Boundaries This activity of the lab is organized by plate boundary type. For each type, first draw the plate boundary, then answer the questions that follow. Be sure to include: • Symbols for earthquakes at different depths (different symbols for deep, medium and shallow if needed) • Label important topographic features (such as volcanoes, mountains, trenches, mid-ocean ridges, etc.) • Label where the older (O) and younger (Y) sea floor is located only if known • Arrows indicating the direction of plate motion • If you used any of your own symbols, add them to the symbol key below I. Convergent Boundaries (Draw the cross sections in the rectangles below) (Continental-Oceanic) Y OY trench Symbol Key mountain range/ volcano ** * A cross section of one type of convergent boundary has been done for you as an example. (Oceanic-Oceanic) Y O * younger ocean crust older ocean crust shallow earthquakes deep earthquakes direction of plate motion (Continental-Continental) 1. Oceanic-oceanic convergent boundary questions a. In which plate do earthquakes occur (subducting/overriding/both)? ________________________________ b. What happens to earthquake depths as you move inland in a subduction zone? ______________________ c. Where do volcanoes occur in a subduction zone? Are they right on top of the plate boundary, inland of the plate boundary on the overriding plate, or inland of the boundary on the subducting plate? Circle one. d. Why do volcanoes occur there? Describe in detail. _____________________________________________ ________________________________________________________________________________________ e. What physical property of oceanic lithosphere makes it able to subduct/sink at convergent boundaries? ________________________________________________________________________________________ 17 Lab 1: Plate Tectonics 2. Continental-continental convergent boundary questions a. At these boundaries, are earthquakes shallow, deep or both? ____________________________________ b. Are there a lot, a few, or no volcanoes associated with these boundaries? __________________________ II. Divergent Boundaries (Oceanic-Oceanic) (Draw the cross section below; use the same symbols as before) 3. Why is the youngest oceanic crust found near the divergent plate boundaries?__________________________ __________________________________________________________________________________________ 4. What properties of divergent boundaries cause it to form ridges of higher elevation than the rest of the ocean floor? _____________________________________________________________________________________ __________________________________________________________________________________________ 5. Now mentally close up the Atlantic ocean by “reversing” the plate movement along the transform faults (at the Mid-Atlantic Ridge). This is what the world looked like about 180 million years ago. What country or continent was adjacent to Boston before the Atlantic opened? ________________________________________ III. Transform Boundaries (Draw a map view below; use the same symbols as before) 6. Describe earthquake locations and depths at transform boundaries. What do you think causes earthquakes at these plate boundaries? Why is the pattern different than at convergent boundaries? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 18 Lab 1: Plate Tectonics Activity 2: Google Earth questions For this activity, you will need to use Google Earth software, which is on all ATUS computer labs at WWU. If you’d like to load this software on your own computer, it is free to download at http://www.google.com/earth/ index.html. Use Google Earth to open some files to aid our investigation of plate tectonics. Open the Canvas page for this lab and go to Modules 1 Lab 1 1 Lab 1 - Plate Tectonics.kmz. Now look at Google Earth and you’ll see the plate names and boundaries colored by boundary type. 1. Fly to the Atlantic ocean (use the search box). a. What kind of plate boundary runs the length of the Atlantic ocean? ________________________________ b. Next, fly to Iceland (use the search box again). Considering your answer to the previous question, what do you think has been happening in Iceland, and will continue to happen? ______________________________ ________________________________________________________________________________________ What effect might this have on the size of Iceland? _______________________________________________ 2. Zoom out and look at the entire globe. Notice that some plates have continents and some do not. Can a single plate have both oceanic and continental parts? ____________________________________________________ a. Name two plates that support your answer. ______________________ _________________________ 3. Turn on the Volcanoes layer (Layers window 1 Gallery 1 Volcanoes) in Google Earth. Now fly to western Washington State so that you can see the plate boundaries. Note that all three boundary types are present just offshore. The volcanoes in the Cascade Range are the result of subduction. In this particular subduction zone water is carried down with the subducting plate, causing the mantle to melt and create magma. Melting happens at a depth of around 100 km. The distance between the trench (the plate boundary) and the volcanic arc (e.g. Cascades) is called the arc-trench gap. The arc-trench gap helps us determine whether a subduction zone is steep or shallow. A wide arc-trench gap indicates a shallow subduction zone, whereas a narrow arc-trench gap indicates a steep subduction zone. The arctrench gap is measured from the peak of a volcano directly across the horizon to the trench. a. Using the Google Earth ruler tool (see pg. 7), what is the arc-trench gap for Mt. Rainier? ______________km b. Now investigate Nicaragua. What is the arc-trench gap for Masaya volcano? _______________ km c. In the boxes below, sketch the cross sections for the two subduction zones for which you measures the arctrench gap. On the vertical axis, use 0 km for the Earth’s surface. Plot the trench at 0 km, 0 km (•). Remember, the trench is located where the two plates meet. Label the trench (T), the zone of melting (M), and the location of the volcano (V). Masaya volcano, Managua, Nicaragua Mt. Rainier, WA, USA 100 100 • 0 km -50 -50 -100 -100 -100 0 km • 0 km 100 200 300 -100 0 km 100 200 300 19 Lab 1: Plate Tectonics d. Now fly to the Krakatau volcano just northwest of Jakarta, Indonesia (search for Krakatoa and look for the nearest volcano). Measure and write down the arc-trench gap here (be sure you aren’t measuring the distance to the nearby transform boundary). How does this subduction zone compare to the Cascasdes and Central America? ________________________________________________________________________________________ ________________________________________________________________________________________ 4. Find India on the plate boundary and scientific specialty maps. a. The Indian plate collided with Eurasia approximately 45 million years ago. Curiously enough, India did not simply stop after the onset of the initial collision. Over the last 45 million years, India has continued to plow into Asia at the remarkable rate of about 5 cm/year! How many kilometers has India pushed its way into Asia in the last 45 million years? Show all work for your calculations (no calculations, no credit). 1 km = 1000m 1 m = 100 cm _______________km b. What outstanding topographic feature do you think resulted from this collision? _____________________ c. Let’s put that distance into perspective. Imagine that a change in the plate tectonic environment of Washington State caused it to plow its way eastward as far as India has advanced into Asia since the collision. What state or region would be Washington’s eastern most neighbor (instead of Idaho)? Use the Google Earth measuring tool to help you. __________________________________________________________________________ 5. Find California on the plate boundary and scientific specialty maps. a. Los Angeles is on the west side of the San Andreas transform fault system. Movement along the fault is carrying LA northwest (with respect to North America) at an average rate of approximately 3.2 cm/year. Assuming that the motion will continue in the same direction and at the same rate for the next few hundred million years, how many kilometers will Los Angeles have traveled in 27 million years? Again, show all work for your calculation. _______________km b. Assuming the Pacific Plate continues to move northwest, carrying Los Angeles with it, which state might LA collide after it travels about 3,500 km? Be as specific as you can. ________________________________________________________________________________________ 20 Lab 1: Plate Tectonics 21 Note that the volcanology map only shows volcanoes that rise above sea level! Many more volcanic vents are found on the sea bottom. They generally correspond in location to the regions of sea floor seismic activity shown on that specialty map. Note changes on the large specialty map posted in your lab. Also, note the inset box for the San Andreas fault region - the volcanoes do not occur on the San Andreas fault itself, but occur more inland (toward the center of the conitnent). Lab 1: Plate Tectonics 22 Lab 1: Plate Tectonics 23 Legend in Millions of Years Lab 1: Plate Tectonics 24 Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Rock Cycle The Rock Cycle Every Rock Tells a Story Identifying rocks is an acquired skill. To obtain these skills you must make careful observations and describe the properties that define the rock, such as composition and texture. Based on those properties, interpretations are made about how the rock formed. In most cases, with some exceptions, we rarely witness the actual formation of rocks. One such exception is the formation of volcanic rock from the crystallization of lava. Some of you may have been lucky enough to have seen rocks form at Kilauea volcano in Hawai’i. The Rock Cycle The rock cycle (Fig.1) is a conceptual summary of rock forming processes that occur within Earth and on Earth’s surface. The three main rock types illustrated in the rock cycle (igneous, sedimentary, and metamorphic) form through very specific geologic processes. Furthermore, through weathering, lithification, metamorphism, melting, or crystallization, one type of rock can alter into another. In other words, rocks are recycled and formed into other rocks. Rock type: Igneous Sedimentary Metamorphic General processes Crystallization of molten rock (magma) Weathering of pre existing rocks, deposition and lithification of sediments Pre-existing rocks subjected to increases in pressure and/or temperature, changing their form in the solid state (meta = change, morph = form) Figure 1. The Rock Cycle. The shaded boxes highlight the three main types of rock. Image source: http://www.scienceviews.com. 27 Rock Cycle Rock vs. Mineral Rocks are made of aggregates of one or more minerals or biochemical components (such as plants or fossils). In geology, a mineral has a very specific definition. A mineral is a naturally occurring, inorganic crystalline solid with a fixed chemical formula. Minerals have a set of diagnostic physical properties that can be used to identify the minerals, for example: • Hardness (resistance to scratching) • Cleavage (a mineral’s tendency to break along preferred planes of weakness)* • Fracture (how a mineral breaks not along preffered planes of weakness)* • Effervescence in hydrochloric acid • Taste *A mineral can have both • Magnetism cleavage and fracture, but • Color (a very poor distinguishing property) some only have fracture. Examples of minerals are: quartz, feldspar, mica, amphibole, pyroxene, olivine, calcite, and halite. Granite is an igneous rock typically composed of the minerals quartz, feldspar, and mica. Schist is a metamorphic rock typically composed of the minerals quartz, feldspar, and mica. Shale is a sedimentary rock typically composed of clay minerals. Coal is another sedimentary rock composed entirely of carbon that was derived from plant material. Identifying Rocks I. Texture Hint: For most of us, the texture means the feel or appearance of the surface of an object; whether it has a rough or smooth surface. In geology, the texture of a rock refers to the characteristics of the material that makes up the rock, as opposed to the feel of the outer surface. Rock texture is the size of the minerals (or fragments), their shape, and how they are stuck together. The texture helps determine the origin of the rock (Fig. 2). The texture of the rock is perhaps the most important tool used to determine whether the origin of a rock is igneous, sedimentary or metamorphic. The texture reflects the geologic processes involved in the formation of the rock. Key rock-identifying observations: 1. Size of the mineral (or fragment) constituents that make up the rock Can you see the minerals/grains with your naked eye, or do you need a microscope? Are particles all the same size or a mixture of different sizes? 2. Arrangement of mineral grains is a property that you will eventually use to tell if the rock is igneous, sedimentary, or metamorphic in origin. Are the minerals intergrown together? Are individual particles cemented together? Are there holes in the rock from the escape of gas bubbles? Does the rock have a squashed look? Do the minerals in the rock appear to have a preferred alignment? 3. Shape of the particles that make up the rock not the shape of the hand sample Are the particles that make up the rock angular or rounded? Are they well-formed crystals or rounded fragments? 28 Igneous, Sedimentary, and Metamorphic Textures Rock Cycle Careful examination of rock texture places most (not all) rocks into one of three categories that depend on how they formed Interlocking crystals Common texture: crystalline Particles cemented together Common texture: clastic Banded minerals Common texture: foliated Rock crystallized from magma Lithification of sediment produced rock Rock subjected to increased pressure & temperature causing parallel alignment of minerals Igneous Sedimentary Metamorphic Figure 2. Rock identification based on texture. Observation Texture Interpretation Particles cemented together Clastic Particles transported, deposited, and stuck together (Fig. 3) Parallel alignment of minerals Foliated Growth of minerals in preferred orientation due to pressure conditions (Fig. 4) Interlocking crystals Crystalline Minerals grown together from magma crystallization (Fig. 5) Different sized crystals in a Porphyritic Different cooling rates (associated with extrusive igneous groundmass rocks; Fig. 6) 29 Lab #2: Igneous Rocks Figure 3. An example of a clastic texture. Figure 4. An example of a foliated texture. Figure 5. An example of a crystalline texture. Figure 6. An example of a porphyritic texture. II. Composition Rock composition refers to the minerals or components that make up the rock, which give clues to the environment of their formation. Because they have a definite chemical formula, minerals tell us the chemical composition of the rock. For example, the composition of volcanic rocks can indicate whether the rocks formed in association with a mid-oceanic ridge, a subduction zone, or a hot spot. 30 Lab #2: Igneous Rocks Lab #2: Igneous Rocks The purpose of today’s lab is to introduce you to igneous rocks. By the end of the lab you should be able to distinguish between different igneous rock types and interpret their origin. Objectives 1) Learn that every rock tells a story. 2) Know the difference between a rock and a mineral. 3) Know how to tell whether an igneous rock is felsic, intermediate, mafic, or ultramafic, and what the composition tells us about the tectonic setting of formation. 4) Igneous rock textures to know, and what they mean when you see them. 5) Recognize and describe the meaning of the following igneous rocks • Plutonic: granite, diorite, gabbro, peridotite, dunite • Volcanic: rhyolite, andesite, basalt 6) Conduct an experiment and explore how the density of igneous rocks controls plate tectonics. Materials Pencil (no pens) Textbook Calculator Pre-lab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook, as well as the web links provided on the Canvas site. The ConcepTest will be on material related to plate tectonics from lab 1 and reading material from lab 2 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Igneous minerals Activity 2: Igneous rocks Activity 3: Density and plate tectonics Homework Activities (due the beginning of next lab) Activities on pages 42-44 31 Lab #2: Igneous Rocks Igneous Rocks Origin of Igneous Rocks Igneous rocks originate from molten rock. “Igneous” is derived from the Greek word for “fire” (think of ignite). Molten rock underground is called magma, and molten rock that erupts at the surface is called lava. Cooling of magma and lava produces igneous rocks. Magmas can flow easily or sluggishly, and this characteristic is described as their viscosity (resistence to flow). High viscosity (or viscous) magmas have high resistence to flow and flows slowly. Low viscosity magmas have low resistence to flow and flow easily. Viscosity is controlled by the magma’s chemical composition, fluid vs. mineral content, and temperature. For example, magma viscosity increases as it cools (the magma thickens). For more information about viscosity go to pg. 36. Igneous Rocks Classification Igneous rocks are typically classified on the basis of their texture (crystal size and arrangement) and chemical composition (minerals present). The texture of an igneous rock reflects its cooling history. The composition of igneous rock, to a large degree, reflects its plate tectonic setting during formation. I. Igneous Textures The texture of an igneous rock reflects how the magma cooled and crystallized to form minerals. The size of the crystals depends on the cooling rate. Coarse-grained textures indicate slow cooling (tens of thousands of years), whereas fine-grained and glassy textures indicate fast cooling (months to hours). Texture is used to indicate whether the magma cooled at the surface (volcanic) or deep underground (plutonic). The following are igneous textures: Coarse-grained: Interlocking crystals (typically 1-10 mm) that can be seen with the naked eye. Great thickness of overlying rock insulated the magma, so that it cooled slowly to form large crystals. Igneous rocks exhibiting this texture cooled deep underground. Fine-grained: Small interlocking crystals (typically <1 mm, which are too small to see with the naked eye). Most fine-grained igneous rocks cooled at the Earth’s surface after being erupted from a volcano. Fine-grained textures can also result from shallow intrusions, or if magma is injected into fractures in cooler rock. These injections are called dikes or sills. Porphyritic: An igneous rock texture that is composed of two different distinct crystal sizes (see Fig. 1). Specifically, crystals >2mm in size are called phenocrysts, and they are embedded in a groundmass made of fine-grained crystals (often called a matrix). Porphyritic rocks are interpreted to have undergone two stages of cooling: the phenocrysts would form while the magma is slowly cooling deep under ground, and, when the magma erupts, the groundmass cools quickly when exposed at the surface. Crystal (phenocryst) Groundmass (matrix) Figure 1. A volcanic rock with a porphyritic texture. 32 Lab #2: Igneous Rocks Glassy: Volcanic glass is called obsidian and lacks crystals. Rocks that are very glassy show a characteristic conchoidal (curved) fracture pattern (see Fig. 2). Glassy texture forms when lava cools so quickly, or is so viscous that ions can not migrate through the melt and become arranged in an ordered pattern to form crystals. Pyroclastic: When molten material is erupted from a volcano it can solidify before it hits the ground, yet still be hot enough to weld to other erupted material (Fig. 3). This forms a rock called tuff, which is composed of fragments (of other rocks) and crystals, all embedded in a matrix of ash. Figure 2. Obsidian showing glassy texture and conchoidal fracture. Vesicular: Vesicles are holes in volcanic rock that form as lava solidifies around gas bubbles. These are good indicators of volcanic rocks (plutonic rocks don’t have vesicles). This term can be used as an adjective (e.g. this is a vesicular basalt). The size of the bubbles is often dictated by the viscosity of the magma, with bigger bubbles forming in less viscous magma because they can coalesce more easily. Figure 3. Welded tuff. Some rocks are defined by their vesicles: • Scoria (larger, less abundant bubbles in reddish-black rock, called a scoreacous texture. See Fig. 4) • Pumice (a lot of little bubbles, almost foamy and very light weight, called a pumiceous texture). Pumice often has enough bubble space that it will float in water. Figure 4. Scoria (scoriaceous texture). II. Igneous Compositions Color is a quick way to estimate the chemical composition of most (but not all) igneous rocks. The color of most igneous rocks is controlled by the types of minerals present. To generalize, a darker color commonly indicates that the rock is composed of minerals with a higher iron/magnesium content. A lighter color indicates the rock contains minerals with high silica (SiO2, mineral name quartz) and low iron/magnesium content. Dark colors (such as black obsidian, or nearly black andesite) may indicate the lack of crystals. In these rocks, the black color is a result of the light being absorbed by glass rather than being reflected back to our eyes form mineral grains. Most magmas can be grouped into three broad categories based on their chemical composition. These categories are mafic (less silica, more Mg and Fe), intermediate, and felsic (more silica, less Mg and Fe). In geology, rock chemical composition is presented in oxide form. For instance, Si contents would be listed as SiO2. The average chemical compositions of felsic, intermediate, and mafic igneous rocks are shown in Fig. 5 on the next page. This graph reveals that most igneous rocks are composed of similar elements in different amounts. Note that silica is the most abundant in all three compositional groups, with content ranging from approximately 50% to 70%. The silica content of igneous magmas is very important because it influences the viscosity of the magma, which determines the behavior of the magma/lava. 33 Lab #2: Igneous Rocks Composition of Igneous Rocks 0% 100% Felsic Intermediate Mafic SiO2 FeO+Fe2O3 MgO+CaO Al2O3 Na2O+K2O Silica Iron Magnesium+calcium Alumina Sodium+potassium Figure 5. Average chemical compositions of mafic, intermediate, and felsic igneous rocks. Note that silica (SiO2) is the dominant oxide in all three types of igneous rocks. Igneous Rock-Forming Minerals The minerals present in an igneous rock indicates the rock’s chemical composition. Thankfully, there is a correlation that determines the kinds of minerals that will occur together in a rock. This correlation is determined by the magma’s chemical composition, as well as the pressure and temperature of crystallization (Fig. 6-7). Important Igneous Minerals Mineral Diagnostic Mineral Properties Composition Quartz Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage Felsic Amphibole/ Pyroxene Brown/translucent, soft (scratches with fingernail), 1 good cleavage (flakes off into thin sheets) White/pink/tan, hard (scratches glass), good cleavage in 2 directions Dark (black or greenish gray), hard (scratches glass), good cleavage Olivine Green (weathers to orange), hard (scratches glass), no cleavage Mica Feldspar Mafic Figure 6. Igneous rock-forming minerals and their properties. Composition Mineral Content Felsic Must contain feldspar and quartz, very minor dark minerals (therefore light in color). Intermediate Contain mostly feldspar and some dark minerals (usually amphibole), usually no quartz. Mafic Contain feldspar and abundant dark minerals, no quartz (therefore dark color). Ultra Mafic Contain almost entirely dark minerals such as pyroxene and olivine. No extrusive equivalents. Figure 7. Characteristic minerals for each compositional group. You will need to be able to identify the igneous rock-forming minerals. Luckily, there are only eight common igneous rock-forming minerals, which have been grouped into 4 broad compositional categories listed in Fig. 7 above. For additional information on igneous rock classification refer to the Igneous Rocks and Associated Minerals diagram (Fig. 8). 34 Special Textures (coarse grained) Intrusive (fine grained or porphyritic) Extrusive quartz feldspar mica amphibole Granite Rhyolite feldsparpyroxene amphibole olivine Gabbro Basalt Dark color (black) increasing viscosity increasing silica content feldspar amphibole Mica pyroxene Diorite Andesite Intermediate color (gray) 45 wt% SiO2 olivine olivine pyroxene Peridotite Dunite No common extrusive equivalent Green (from olivine) (can have black flecks) SCORIA PUMICE Vesicles (bubble holes) may or may not occur in any composition of volcanic (extrusive) rock. Typically vesicles are smaller in more felsic magma and larger in more mafic magma. OBSIDIAN 75 wt% SiO2 Minerals Light color (white/pink) Lab #2: Igneous Rocks Figure 8. Igneous rocks identification chart, including important minerals. 35 Lab #2: Igneous Rocks Magma Viscosity As defined previously, viscosity is resistance to flow. A fluid with high viscosity resists flow and is sticky (flows like cold honey; Fig. 9). A fluid with low viscosity is runny (flows like water; Fig. 9). Viscosity determines: • The shape of volcanoes • Whether a volcanic eruption will be explosive or relatively quiet • How easily a magma will rise through the crust to Earth’s surface. This can control where a magma might solidify (whether deep underground or on Earth’s surface). Figure 9. Viscosity differences between water (left) and honey (right). Image source: Vienna University of Technology. Gas bubbles form in magma as it rises. The gas bubbles are less dense (buoyant) than the magma, so they cluster at the top of the magma body. As the gas bubbles cluster, they enduce pressure build-up within the magma body, which pushes the magma upward. Therefore gases that can’t escape prior to an eruption increase the explosive potential of a volcano. Composition Mafic (1050-1300°C) Intermediate (900-1100°C) Felsic (650-1000°C) Silica Content ~50% ~60% ~70% Gas Content Least (1-2%) Intermed. (3-4%) Most (4-6%) Viscosity Low (runny lava) Intermed. (thick lava) High (very thick lava) Common Rock Types Extrusive: basalt, scoria (very abundant) Intrusive: gabbro (abundant in oceanic crust, rare in continental crust) Extrusive: andesite (abundant) Intrusive: diorite (abundant) Intrusive: granite (abundant in continental crust, rare in oceanic crust) Extrusive: tuff (abundant) rhyolite, obsidian (less abundant) Figure 10. Viscosity and behavior of felsic, intermediate, and mafic magmas. 36 Common Volcanic Landforms Flood basalt, plateaus, ocean floor cinder cones, shield volcanoes, small calderas Pyroclastics Cinders, bombs Composite, volcanoes, large calderas Tuff, ash fall Volcanic domes, large calderas filled with ash Pyroclastic flows, tuff, pumice, ash fall Lab #2: Igneous Rocks Density of Igneous Rocks Density is an important property of igneous rocks. Consider the questions: Why are there deep ocean basins and why are there high continents? Why is continental crust thicker than oceanic crust? Why is oceanic crust subducted and not continental crust? These questions can be answered with density differences. Imagine two boards floating in a pool, one made of dense plywood and another made of light Styrofoam. Even if the boards are the exact same volume, the plywood floats a little lower in the water because it is more dense. The same is true with the Earth’s crust, where continents are made of material that is less dense than the ocean floor. Some rocks have densities so great that they rarely make it out of the mantle. If you know the densities of an igneous rock, you can infer the tectonic setting. Read the section below for a little more information about the tectonic settings of various igneous rocks, and study Fig. 11 on the next page. Density is a measure of the amount of mass per unit volume, such as g/cm3 or kg/m3. Density = Mass (g) Volume (cm3) Note: 1mL = 1cm3 Tectonic Settings: Where Igneous Rocks Come From After many observations worldwide, detailed chemical analyses on scores of rock samples, and with countless scientific experiments, geologists have derived theories about how and where rocks melt, and what happens to the magma during its journey prior to solidification. The mantle is composed of ultramafic rocks. Ultramafic rocks have silica contents that are lower than mafic rocks, and they are dominantly made of dark minerals (e.g. olivine and pyroxene). When the ultramafic rocks in the upper mantle are partially melted, mafic basaltic magma is created. Although melting rocks is easiest when water is present, much of the basaltic magma produced at divergent plate boundaries (such as mid-ocean ridges, continental rift zones, or hot spots) occurs without water. This melting, called dry decompression (partial) melting, is caused by expansion of hot rock as it rises through the mantle. As the magma gets closer to the surface, it is under less confining pressure and can expand to become liquid. Intermediate andesitic magmas typically form when basaltic magmas, formed from the wet decompression melting of mantle rock in subduction zones, incorporate continental material as they rise to the surface. Felsic rhyolitic magmas typically form from wet partial melting of the upper mantle and continental rock. Most felsic magmas are generated at depth in continental collision zones. For this reason the cores of many mountain ranges are composed of felsic rocks, and why eruptions of rhyolite occur at subduction zone volcanoes. Felsic magmas can also occur at continental hotspots. To better illustrate where different igneous rocks tend to form, a cross-sectional view of plate boundaries is shown in Fig. 11. 37 38 Figure 11. Tectonic environments of igneous rocks Upper Mantle (“plastic” ultramafic) Wet partial melting of the upper mantle Subduction arc volcanism: Extrusive Intermediate and Extrusive Felsic Mid-ocean ridge: Continental crust: Extrusive Mafic near Intrusive Felsic and Intrusive surface; Intrusive Intermediate Mafic at depth Hotspot volcanism: (e.g., Hawaii) Extrusive Mafic near surface; Intrusive Mafic at depth Dry partial melting (decompression melting) of the upper mantle (ultramafic) Oceanic crust: Extrusive Mafic Lab #2: Igneous Rocks Lab #2: Igneous Rocks In-Class Activities Activity 1: Identifying Common Igneous Minerals I. Minerals Learn to recognize the important rock forming minerals. In groups of 3 or 4, use Fig. 6 as a guide to the diagnostic properties that will help you identify the minerals in the mineral tray. The numbers listed here correspond to the numbers on the mineral samples. 1. (2 samples) _________________________ 2. (2 samples) ___________________________ 3.___________________________________ 4._____________________________________ 5. (2 samples, light = muscovite, dark = biotite)_______________________________ II. Minerals in Rocks and Rock Identification For rock samples 6 and 7, identify the minerals in each rock and use Fig. 8 to identify the coarse-grained igneous rock based on the minerals it contains. Cleavage planes (if the mineral has cleavage) are visible when they reflect light (glint) as you rotate the rock through different lighting directions. 6. Rock sample 6 a. Minerals: Translucent, gray mineral: ____________________ White or pink opaque mineral: _________________ Dark colored mineral(s): ______________________ b. Composition (felsic, intermediate, mafic or ultramafic?): ______________________ c. Rock name: ________________________________ 7. Rock sample 7 a. Minerals: Green mineral: _____________________________ Black flecks (if present): _____________________ b. Composition (felsic, intermediate, mafic or ultramafic?): ______________________ c. Rock name: ________________________________ 8. It can be difficult to distinguish between granite and diorite. a. Which rock will contain very little quartz or mica? _________________________________________ b. Which of the two rocks will have a higher percentage of dark, mafic minerals? ___________________ TA CHECK ________________ 39 Lab #2: Igneous Rocks Activity 2: Identifying Common Igneous Rocks The purpose of this activity is to learn to differentiate igneous rock samples according to their texture (primarily grain size), and composition (based on visible minerals and color). 1. Separate the intrusive (coarse-grained) rocks in the Activity 2 tray from the extrusive (fine-grained or porphyritic) rocks. Texture Interpretation Fine-grained: few or no visible crystals (<2mm) Fast cooling at or near surface of the Earth Porphyritic: mix of coarse and fine grained textures Two cooling stages Coarse-grained: visible crystals (>2mm) Slow cooling at great depths 2. Arrange the fine-grained/porphyritic and coarse-grained piles in order from light-colored to dark-colored as shown below. Your ability to judge can be improved by looking at the minerals in the coarse-grained samples as you did in Activity 1. This ordering approximates the chemical composition of the samples. Compositions Felsic Intermediate Mafic Ultramafic Fine-grained Light-Colored Intermediate Color Dark-Colored (no common equivalent) Coarse-grained Light-Colored Intermediate Color Dark-Colored Dark or Green 3. Once you’ve arranged the rocks, ask your TA to come check your work. Now record the sample # and rock name in the appropriate space in the chart on the next page. Use Fig. 8 to help you identify the rocks. Be sure to include rock texture descriptions if the rocks are porphyritic or vesicular. Color Light Medium Dark Dark/Green Composition Felsic Intermediate Mafic Ultramafic Texture: Fine-grained (extrusive/ volcanic) Sample #: ________ Sample #: ________ Sample #: ________ Name:___________ Name:___________ Name:___________ RARE (no sample) Texture: Coarse-grained (intrusive/ plutonic) Sample #: ________ Sample #: ________ Sample #: ________ Sample #: ________ Name:___________ Name:___________ Name:___________ Name:___________ TA CHECK ____________ 40 Lab #2: Igneous Rocks Activity 3: Understanding Density and Plate Tectonics Much of the reason plate tectonics works is because of density differences between major sections of the planet. In this activity, you first identify some additional igneous rock samples, and then measure their physical properties (mass and volume). With these data you can then calculate their densities. Follow the steps below. 1. After looking at the rock samples for this activity, identify each rock and write the name in the second column of the chart below. 2. Using the scale, weigh each rock sample and write down your measurement in the table. Always include units. 3. To measure the volume of the sample we will measure the volume of water that is displaced when the rock is submerged. Step 1: the graduated cylinder should be about half full of water. Before you submerge the rock, very carefully and accurately measure the top of the water. Always note the value of a tick mark. Step 2: gently submerge the rock in the cylinder, trying hard not to get your hands (or anything else) wet we want to keep all the water in the cylinder. Step 3: very carefully and accurately measure the new height of the water. Step 4: calculate the change in volume of the water and record your answer in the table. Remember that 1 mL = 1 cm3 4. Calculate the density and record it in the table. If you need a hint on how to do this, refer back to pg. 37. 5. Finally, infer the tectonic setting. Where would you expect to find the most dense rock? Where would you expect to find the least dense rock? Choose from the major divisions of the Earth: continental crust, oceanic crust, mantle, and core. Sample # Rock Name (identify) Mass (measure) Volume (measure) Density (calculate) Likely Tectonic Setting 4A 4B 4C TA CHECK ____________ 41 Lab #2: Igneous Rocks Homework Activities Activity 1: Density Based on your results from your density measurements, answer the following questions. 1. Which type of igneous rock subducts at convergent boundaries? Please explain why. __________________________________________________________________________________________ __________________________________________________________________________________________ 2. In an oceanic-oceanic convergent boundary, which plate will subduct? Please explain why. __________________________________________________________________________________________ __________________________________________________________________________________________ 3. The major compositional layers of the Earth are the core, the mantle, and the crust. a. Which layer is the most dense? Why?________________________________________________________ b. Which layer is the least dense? Why? ________________________________________________________ Activity 2: Google Earth The remainder of the homework questions will involve the use of Google Earth. Open up the program, then go to the Canvas page for your Geology 101 lab section and navigate to Modules 1 Lab 2. There you’ll find a series of Google Earth files. The files are named by the question to which they correspond in the homework questions below. Need a Google Earth refresher? Go to page 7. 1. Sierra Nevada Batholith. Batholith is the term for the largest class of igneous intrusion, and the Sierra Nevada batholith forms the core of the Sierra Nevada Mountains in California and Nevada. There are exposures of granite in places like Yosemite National Park. a. Open the Lab2_1a_SierraNevadaBatholith.kmz file. This file will place a red polygon outlining the batholith. Use the transparency slider at the bottom of the Places panel to help get oriented. To get a sense for the size of this intrusion, measure length in kilometers. ______________km b. Open the Lab2_1b_HalfDome.kmz file (be sure to turn off the batholith layer from 1a). This will take you to the Half Dome at Yosemite National Park, which was carved by glacial ice flowing over the granite batholith. In meters, measure the minimum thickness of the batholith by determining the difference in elevation between the top of Half Dome and the floor of the valley. Note: If you can’t see the lat/long/elevation, go to the View menu and make sure the Status Bar is checked. ________________m 42 Lab #2: Igneous Rocks 2. Tectonic Associations with Igneous Rocks For each of the following questions, open the Google Earth placemark with the same question number. The files for this activity are located on the lab Canvas page under Modules 1 Lab 2. Hint: Are you on continental crust? Oceanic crust? Refer to the in-class activities for help. a. Lab2_2a_EXTRUSIVE.kmz. Investigate this area by flying around. What type of igneous rock would you expect to see at this location (rock name)? _______________________ What kind of texture would you expect this rock to have (fine- or coarse-grained)?_______________________ What composition would you expect of this rock (ultramafic, mafic, intermediate, felsic)? ________________ b. Lab2_2b_INTRUSIVE.kmz. Investigate this area by flying around. This location is meant to be several kilometers underground. What type of igneous rock would you expect to see at this location (rock name)? _______________________ What kind of texture would you expect this rock to have (fine- or coarse-grained)?_______________________ What composition would you expect of this rock (ultramafic, mafic, intermediate, felsic)? ________________ c. Lab2_2c_INTRUSIVE.kmz. Investigate this area by flying around. Hints: • Look at pictures of the area (you may need to turn on the Photos layer) • Tilt the view angle (Shift + ↓) Name two igneous rocks that you would expect to see at this location, and indicate whether they are felsic, intermediate, mafic, or ultramafic. ___________________________(rock name) ________________________ (composition) ___________________________(rock name) ________________________ (composition) d. Investigate Lab2_2d_Hawaii.kmz by flying around as you have for the previous locations. Note the various colors along the ridge crest, particularly the dark material. This dark material is a lava flow, seen from an areial view. What is the tectonic setting?_______________________________________________________________ What do you think the texture of these rocks is likely to be (fine- or coarse-grained)? ____________________ What do you think the composition of these rocks might be (felsic, intermediate, mafic, or ultramafic)? ________________________________________________________________________________________ Now open Lab2_2d_MtShasta.kmz. Compare the Hawaiian lava flows you just looked at to those at Mt. Shasta (size, shape, length). _________________________________________________________________ ________________________________________________________________________________________ Refer to the pre-lab reading material and review lava behavior. What do you think causes the differences between these flows?_________________________________________________________________________ ________________________________________________________________________________________ e. Lab2_2e_EXTRUSIVE.kmz. Investigate this area by flying around. Name two igneous rocks that you would expect to see at this location, and indicate whether they are felsic, intermediate, mafic, or ultramafic. ___________________________(rock name) ________________________ (composition) ___________________________(rock name) ________________________ (composition) 43 Lab #2: Igneous Rocks f. Open Lab2_2f_OmanOphiolite.kmz. This is the Oman ophiolite, one of the best ophiolite examples in the world. An ophiolite is a sliver of Earth’s mantle that has been pushed on top of the crust. This area is one of the very few places we can actually see Earth’s mantle. What igneous rock would you expect the Oman ophiolite to be made of? _______________________________ What kind of texture would you expect this rock to have (fine- or coarse-grained)? ______________________ What composition would you expect of this rock (ultramafic, mafic, intermediate, felsic)? _________________ Activity 3: Putting It All Together One of the really cool things you should learn from this lab is that you can predict the rock types present at different tectonic settings (and vice versa). Label the plate tectonics diagram below with the igneous rock type that is most common in each location. To help you, refer to the prelab reading, as well as your answers to the previous activity. One of these has been done for you as an example. Hint: Some rocks form in more than one tectonic setting (see Fig. 11). Extrusive Extrusive OR Rhyolite Intrusive Extrusive Intrusive Extrusive Intrusive Intrusive (hot spot) (lithospheric mantle) (asthenospheric mantle) 44 (mid-ocean ridge) (subduction zone) Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Lab #3: Sedimentary Rocks and Depositional Environments Lab #3: Sedimentary Rocks and Depositional Environments The purpose of today’s lab is to introduce you to sedimentary rocks. By the end of the lab you should be able to distinguish between different sedimentary rock types and interpret their depositional history. Objectives 1) Know the processes through which sedimentary rocks form. 2) Be able to identify common sedimentary minerals. 3) Be able to identify common sedimentary rocks. 4) Be able to interpret the origin of sedimentary rocks on the basis of their texture and composition. 5) Be able to create a geologic history by interpreting a sequence of sedimentary rocks. Materials Pencil (no pens) Textbook Calculator (Homework) Pre-lab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook, as well as the web links provided on the Canvas site. The ConcepTest will be on material related to igneous rocks from lab 2 and reading material from lab 3 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Depositional environments Activity 2: Geologic rock record Activity 3: Sedimentary rocks Homework Activities (due the beginning of next lab) Activities on pages 59-64 47 Lab #3: Sedimentary Rocks and Depositional Environments Sedimentary Rocks The interaction of pre-existing rocks with the hydrologic cycle at the Earth’s surface results in the formation of sedimentary rocks. Sedimentary rocks typically form in layers, such as the colorful layers exposed in the Grand Canyon. Locally, the Chuckanut Mountains consist of sedimentary layers of conglomerate, sandstone, siltstone, and coal. Sedimentary rocks form through two major processes: 1. Detrital and clastic sedimentary rocks are derived from the weathering of pre-existing rock, where the sediment is transported, deposited, buried, and lithified (solidified into stone). Examples of such rocks are: conglomerate, sandstone, and shale. 2. Biological and chemical sedimentary rocks are a result of the settling and lithification of precipitates (such as mineral grains) and organisms (such as plankton). Examples of such rocks are: limestone, halite, chert, and diatomite. Origin of Sedimentary Rock There are 4 main steps in the formation of most sedimentary rocks: I. Weathering of pre-existing rocks II. Erosion and transportation of sediments or ions in solution III. Deposition IV. Burial and lithification I.Weathering Weathering of pre-existing rocks produces sediment (Fig. 1). There are two main ways that rocks can weather: Mechanical (physical) weathering is the process of breaking rock material into smaller particles. If you hit a rock with a hammer and it breaks into various-sized pieces, you have physically weathered the rock by decreasing the particle size. This increases the surface area without changing the chemical composition of the minerals. Chemical weathering occurs when minerals interact with the environment and are chemically changed. Some minerals dissolve in water (e.g. halite), or oxidize (e.g. iron rusts) to form ions in solution or new minerals. Feldspar reacts with water to form clay, which is the constituent of shale, the most abundant sedimentary rock. The main products of mechanical and chemical weathering are: Lithic (rock) fragments: broken pieces of parent (pre-existing) rock. Resistant mineral grains: some minerals are relatively stable at the Earth’s surface and are resistant to alteration. Quartz is the most common resistant mineral. Clay: clay is formed by the chemical weathering (specifically hydrolysis, the chemical breakdown of a compound due to reaction with water) of feldspar minerals. Besides being a mineral, the term clay also refers to sediment that is smaller than 1/256 mm. Ions in solution: chemical weathering of non-resistant minerals releases ions such as Si, Ca, Na, Fe, Mg. These ions are present in lakes, rivers, groundwater, and the ocean where chemical sedimentary rocks form by precipitation or evaporation. Ions dissolved in groundwater can precipitate and cement clastic particles together. Ion precipitation can also form beautiful geodes, agates, and thundereggs by filling rock cavities (holes). 48 Lab #3: Sedimentary Rocks and Depositional Environments Weathering products are dependent on the composition, grain-size, and the type and degree of weathering. For example, weathering of a coarse-grained granite will produce sand-sized particles, clay minerals, and dissolved ions. However, since basalt is fine-grained and does not contain any resistant minerals, basalt will eventually break down completely into clay minerals and dissolved ions. Weathering Products Visible Grains Clay • Quartz • Rock fragments • Lightly weathered nonresistant minerals Clastic Rocks Sediment ≥256mm 64mm 4mm 2mm boulders cobbles pebbles granules 1/16mm sand 1/256mm silt ≤1/256mm clay Ions in Solution Na - sodium Ca - calcium Mg - magnesium Chemical Rocks Fe - iron Si - silicon Biochemical Rocks Rock Compound Rock Compounds Rock breccia, conglomerate CaCO3 NaCl SiO2 CaSO4+2H2O limestone rock salt chert gypsum CaCO3 fossils Powdered CaCO3 Powdered SiO2 Crystalline SiO2 Fossilized C fossiliferous limestone chalk diatomite chert coal sandstone siltstone mudstone, shale Figure 1. Weathering products and the sedimentary rocks they form. II. Transportation Weathering products that are eroded from their source can be transported by moving water, ice, or wind. Sediment can undergo physical changes that affect the texture of the sediment. The three main sedimentary textures that tell us about the transport history of sediments are listed below: Grain size of a sedimentary rock can be interpreted to indicate several things. 1. The energy of the environment at the time of deposition. The higher the energy (e.g. the swifter the water), the larger the grain size that can be moved. 2. The grain size of sediment generally decreases as it gets farther from the source area due to breakage, abrasion, or chemical weathering. Rounding is the removal of sharp edges of rock fragments and resistant mineral grains as they grind against one another or the ground surface. Angular grains have not experienced as much abrasion as well-rounded grains (Fig. 2). Figure 2. Rounding progression of grains. 49 Lab #3: Sedimentary Rocks and Depositional Environments Sorting is a process through which sediment grains are selected and separated according to grain size, and in some cases grain shape or density (Fig. 3). Well-sorted sediments indicate constant energy over time. Poorly-sorted sediments may indicate inadequate time to winnow and sort grains. These textures are also indicators of energy. Figure 3. Sorting of grains. Fast, turbulent waters are high energy environments, and calm waters are low energy environments. Higher energy environments produce large, angular, poorly-sorted sediments, whereas low energy environments produce small, rounded, well-sorted sediments. III. Deposition Sediment is deposited when transporting agents, such as running water, glacial ice, or wind, lose energy and can no longer transport the sediment load. Deposition also refers to the accumulation of chemical or organic sediment, such as calcium carbonate (CaCO3), clamshells on the sea floor, or plant material in a swamp. IV. Burial and Lithification Sediments are deposited in layers on top of one another, which packs loose sediment grains tightly together (compaction). Compacted sediment can be hardened even further by the precipitation of cement (ions dissolved in circulating groundwater) in the pore space between the grains. Common cements are calcite (CaCO3), silica (SiO2), and iron oxides. Sedimentary Minerals Most sedimentary rocks are transported and deposited in water, and those rocks that are not formed in water often have groundwater moving through them. The dissolved ions in the groundwater can form sedimentary minerals, either in layers or filling cracks in rocks. Below is a chart listing the key properties of a few important sedimentary minerals (Fig. 4). Important Sedimentary Minerals Mineral Quartz Gypsum Calcite Halite Limonite Feldspar Diagnostic Mineral Properties Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage White (can be almost clear), soft (can be easily scratched with a fingernail), good cleavage in 2 directions (but not at 90o) White, crystals can be rhombic, reacts (fizzes) with dilutes acid (HCl), soft (scratched with a glass but not with a fingernail) White or translucent, soft, 3 cleavage planes (cubic crystals), salty taste (taste at your own risk!) Yellow-orange, soft, amorphous (no constant or regular shape) White/pink/tan, hard (scratches glass), good cleavage in 2 directions Figure 4. Common sedimentary minerals and their properties. 50 Lab #3: Sedimentary Rocks and Depositional Environments Depositional Environments Sediments accumulate in depositional environments such as alluvial fans, river channels, flood plains, deltas, lakes, desert valleys, beaches, shallow marine, and the deep sea floor. An important task of a geologist who studies sedimentary rocks is to interpret the ancient environment in which the rock formed (Fig. 5-9). By making detailed observations, a geologist can read the many clues that tell the depositional story of a rock sequence. Property Color Texture Observation Red, orange, and yellow colors occur where Fe- and other oxides form Black Grain size Rounding Sorting Transported minerals or fragments Composition Minerals that form in sedimentary environments Sedimentary Structures Bedding, cross-bedding, graded bedding, ripple marks, mud cracks, etc. Fossils Remains of animals of plants such as shells, bones, teeth or leaves Interpretation Oxidizing environment on continents Suggests carbon that was preserved in a reducing environment (i.e. swamps or deep marine) Energy or distance from source Abrasion history Constancy of energy Indicates the type of source area Conditions in the environment must be just right to form rocks made of calcite, halite, gypsum, quartz, or iron-oxides Indicate mechanism of deposition, such as wind or water currents, wind moving over shallow water, underwater density currents, dessication of mud, etc. Organisms live in distinctive environments or niches as they have specific requirements to survive Figure 5. Properties you can use to interpret the depositional environment of sedimentary rocks. Figure 6. a. An illustration of cross-bedded layers. Cross-beds are common indicators of a dune environment. b. Ripple marks are common indicators of tidal flats, and can be used to tell current direction. c. Mud cracks help geologists determine the up-right direction during deposition. 51 52 Figure 7. Depositional environments of different sedimentary rocks. Deep Marine Submarine Fan Lagoon Playa Lake (Evaporite Rocks) River (Headwaters) Desert Dunes Alluvial Fan Glacier Swamp Lake Beach Dunes Beach River Shallow Marine Delta Delta Tidal Flat Deep Marine Abyssal Plain Sedimentary Depositional Environments Seamount/ Guyot Lab #3: Sedimentary Rocks and Depositional Environments Lab #3: Sedimentary Rocks and Depositional Environments Alluvial fan Glacial Dune Terrestrial (Continental) River Lake Swamp Delta Lagoon Transitional (marine coastlines, where the sea meets Beach the land) Tidal flat Shallow marine Marine Deep marine Abyssal plain A deposit shaped like an open fan that forms at the base of mountains where a stream suddenly widens, spreads out, and dumps its load. Rock: conglomerate, breccia Till - sediment melted out of glacial ice and deposited. Stratified (layered) drift - gravels sorted and deposited by glacial meltwater streams. Rock: conglomerate, sandstone, mudstone Wind-deposited accumulations of mostly sand-sized particles. Common in deserts and along coastal areas. Rock: sandstone Channel - where river water flows, channel deposits can be boulder, gravel, to sand-sized particles. Rock: conglomerate or sandstone Point bar - sand or gravel bar at the inside meander bend. Rock: sandstone (w/ cross-bedding) Flood plain - silts, sands, mud deposited when a river overflows its banks and floods Rock: siltstone, mudstone/shale Freshwater low-energy environment where fine-grained sediments are deposited. Rock: mudstone/shale, limestone Low depression, poorly drained soils Rock: coal Where a river empties into the sea. Forms steeply sloping cross-bedding as delta front grows seaward. Rock: siltstone, sandstone An oceanic-sea water and freshwater environment protected from wave energy by an offshore reef. Rock: limestone, mudstone, chalk The transitional zone between the sea and the land, where waves break on the shore, very high energy. Rock: sandstone, conglomerate Low flat area adjacent to the sea which is affected by the tides, exposed at low tide and underwater at high tide. Typically composed of silt and mud and commonly has ripples. Rock: siltstone, mudstone/shale Offshore, extends to about the edge of the continental shelf. Rock: mudstone/shale, limestone, chalk Fine muds and microfossils, foraminifera and radiolaria. Rock: mudstone, chert Figure 8. Common depositional envirments and their corresponding sedimentary rocks. 53 Lab #3: Sedimentary Rocks and Depositional Environments Sedimentary Rock Conglomerate Breccia Sandstone Mudstone or Shale Limestone Chalk Chert Coal Possible Environment of Deposition Alluvial fan, glacial region, near rivers, beaches Alluvial fan, base of a cliff Glacial area, rivers, dunes, beaches Rivers (floodplains), lake beds, tidal flats, deep marine Shallow marine, lagoon (and some very large freshwater lakes) Shallow marine, lagoon Deep marine Swamp Figure 9. This chart is another way to look at some of the information listed in Fig. 8 on the previous page. Classification of Sedimentary Rock Begin by carefully observing the characteristics of the rock sample, then refer to the chart on the next page. Choose and follow the path that best fits your observations. The flow chart begins with the big picture and slowly narrows down to detailed characteristics. Step1: Determine whether the rock is clastic or detrital (contains sediment from pre-existing rocks) or chemical or biological (formed from once living material or ions precipitated from solution). Step 2: If clastic or detrital, determine the rock’s grain size and roundedness/angularity. If chemical or biological, determine the rock’s hardness and reaction to HCl. Step 3: Continue to follow the flow chart and compare the detailed characteristics with your observations. Step 4: Identify the rock based on your observations and the chart’s descriptions. 54 Lab #3: Sedimentary Rocks and Depositional Environments Clastic rocks can have fossils! (i.e. fossiliferous sandstone or fossiliferous shale) Figure 10. Sedimentary rocks classification flow chart. 55 Lab #3: Sedimentary Rocks and Depositional Environments Interpreting Geologic History from Sedimentary Rocks When one type of sedimentary rock is forming in a certain place (like a sandstone on a beach), another type of sedimentary rock is forming nearby at the exact same time (like limestone in the shallow ocean floor and shale on the deepest ocean floor). After these sediments are deposited, more sediment is deposited on top of them (Fig. 11). The weight of the overlying sediments helps to compact the older (lower) sediments, which lithifies them. Understanding this process helps us recognize that the rock at the base of a stack of rocks represents the oldest material. Figure 11. Sedimentary layering in Zion National Park. If sea level changes, the environment of deposition for a given location may change as well. For example, if sea level rises, a sandy beach may become flooded and the sand will be buried by shallow water organic material. So, when we see a sequence of rocks with beach-like sandstone that is overlain by limestone, we can interpret this to mean that the water got deeper in that location. Changing water levels can occur through sea level change (resulting from melting or freezing large quantities of glacial ice), or through uplift of the land. The two processes that cause uplift are: 1. Compression through late tectonics: Imagine laying a pancake on a table and squeezing if from the sides - some areas would wrinkle up. In geology, we refer to the wrinkling as uplift. 2. Land erosion: erosion is a slightly more complicated issue, but the results are similar. As erosion removes material from the surface of the lithosphere, the lithosphere does not weigh as much in that location. Because the lithosphere is “floating” on the asthenosphere, making the lithosphere lighter actually causes it to rise higher in the asthenosphere. This moves rocks from the middle of the crust closer to the surface where continued erosion will eventually expose them. When we see a stream-cut canyon with sedimentary layers exposed in the canyon walls, we can interpret: 1. the layers on either side of the canyon were probably connected at one point, representing a broad layer of sediment that was deposited and lithified, 2. the oldest material is on the bottom and the rocks get progressively younger toward the top, and 3. the youngest event to occur in this canyon is the one that is going on right now, the erosion of the stream through the sediments (even if some of the rocks exposed in the canyon walls were deposited by a stream, that happened millions of years ago in a totally different stream system). Describing the events that took place and formed a rock sequence is called a geologic history. You’ll be asked to do this in your homework, so if you have any questions about interpreting the geologic history of an area, ask your TA. 56 Lab #3: Sedimentary Rocks and Depositional Environments In-Class Activities Activity 1: Identifying Common Sedimentary Minerals The purpose of this activity is to become familiar with common or important sedimentary minerals 1. Divide into groups of 3 or 4. Every group will use one set of sedimentary minerals (tray 1). 2. Use Fig. 4 as a guide to the diagnostic properties that will help you identify the mineral samples in the tray. Sample # Mineral Name Best Identifying Characteristic (shape, reactivity, cleavage, etc.) 1 2 3 4 Which of these minerals are also common igneous minerals? _______________________________________ Activity 2: Describing Sedimentary Textures Identifying specific minerals in sedimentary rocks is sometimes very difficult, so we rely much more heavily on the texture of the rocks. Because sedimentary rocks are formed differently than igneous or metamorphic rocks, we use different textural terms to describe sedimentary rocks. Look at the table below, and look at the jars of sediment in tray 2. 1. For each of the primary sediment characteristics (sorting, grain size and rounding), determine which of the sediments best fits the textural term listed. Sorting well sorted poorly sorted Grain Size large grain size small grain size Rounding rounded angular Sample # 2. What do these differences between the sediments mean with respect to the transport history?______________ __________________________________________________________________________________________ 3. What do these differences between the sediments mean with respect to the energy level of the environment in which they formed?________________________________________________________________________ __________________________________________________________________________________________ TA CHECK__________ 57 Lab #3: Sedimentary Rocks and Depositional Environments Activity 3: Identifying Common Sedimentary Rocks Investigate the samples in tray 3. In your groups, follow the steps below: Step 1: Make observations and determine diagnostic features and characteristics. Step 2: Use your observations to interpret the conditions of the sedimentary depositional environment. Step 3: Name the samples using the sedimentary rocks classification flow chart (Fig. 10). Observations (list at least 3) Interpretations (list all that apply) E.g. texture (grain size, sorting, rounding), composition, fossil types, hardness, reaction to acid, etc. What is its depositional environment? (Fig. 7 - 9) A B C D E F G H TA CHECK__________ 58 Inference What is the main composition if it is chemical/ biological? (Fig. 1) What is the energy level if it is clastic/detrital? Rock Name Lab #3: Sedimentary Rocks and Depositional Environments Homework Activities Activity 1: Interpreting Depositional Environments Look at the diagram below (refer to your pre-lab reading material for help). Fill in the blank boxes with rock names that are reasonable given the environment of deposition. Use each rock name only once. Conglomerate 59 Lab #3: Sedimentary Rocks and Depositional Environments Activity 2: Understanding A Geologic Rock Record mountain coast/beach tidal flat shallow marine deep marine continental shelf Above is an image from Google Earth of North America’s east coast. The dark shading off the coast is the drop off that marks the end of the continental shelf. On the following page there are three identical, generalized cross sections (vertical slices) along the dark line. The cross sections show the transitions from mountain→beach→tidal flat→continental shelf→deep ocean abyss. Each cross section represents a single point in time in Earth’s history, and your job is to name the different rocks that form in the various environments of deposition. 1. Fill in the blank. Start with Time I (top cross section). In each box, write the name of the sedimentary rock type you would expect to be deposited in each environment (note: there may be more than one correct answer). Next, in Time II (the middle cross section), notice the difference in sea level from Time I. • Fill in the rock types that were deposited during Time I (copy your answers from the first step in the boxes labeled 1). • Considering the change in sea level, write the rock type that is currently being deposited (write these in each of the boxes labeled 2). Note: if the environment hasn’t changed much and the same rock will form as did in Time I, that’s OK. For Time III, copy your answers from Time I and Time II and write them in the appropriate boxes. Once you’ve finished filling in all the boxes, answer the questions on the page following the cross sections. 60 Lab #3: Sedimentary Rocks and Depositional Environments Note: not to scale Time I Sea Level 1 1 1 Time II Sea Level 2 2 2 1 1 1 Time III Sea Level 3 3 3 2 2 2 1 1 1 61 Lab #3: Sedimentary Rocks and Depositional Environments 2. Look back at the second column in Time III (it has a star above it). Copy the rock names you wrote down to the matching boxes below and complete the table. Rock Type (copy names over) Depositional Environment Energy Level (low, intermediate, high) 3 2 1 3. Think about the changes between Time I and Time II. What geologic events could have caused the change in environment, and therefore the changes in energy level? Refer to Geologic History section in your pre-lab reading. ___________________________________________________________________________________ __________________________________________________________________________________________ 4. Think about the changes between Time II and Time III. What geologic events could have caused the change in environment, and therefore the changes in energy level? Refer to Geologic History section in your pre-lab reading. ___________________________________________________________________________________ __________________________________________________________________________________________ Activity 3: Compaction of Sediments If the rocks in a sequence were uplifted above sea level, and a stream were to cut through the rocks, we would see a stack of rocks in the canyon walls that all formed in the same location but at different times and in different depositional environments. How long does this take? Let’s investigate. 1. Deposition: the principle of uniformitarianism says that the processes that are going on today are the same as those that have acted in the past (“The present is the key to the past”). Modern depositional rates of limestone in the Caribbean Sea are 0.5cm/1,000 years (kyr). Given that rate, how long would it take to deposit just one layer from this rock sequence? Assume each layer is 100 m thick. Show your work (no calculations, no credit). __________________ years 2. Compaction: sediment gets substantially compacted during lithification. For limestone, a typical amount of compaction is 20% that of deposition. Given this, and using your previous answer, how long did it really take to deposit one layer? Show your work (no calculations, no credit). __________________ years 3. Assuming this rock sequence has 4 limestone layers, as well as a constant* compaction rate during the deposition of all layers, how long did it take to deposit the whole stack of rocks? Use your previous calculation to answer this question. *in reality, these rates change over time depending on many factors; we’re assuming constant here just to make the calculations simpler. __________________ years 62 Lab #3: Sedimentary Rocks and Depositional Environments Activity 4: Constructing A Geologic History By now you should have a good idea of how a single location can have lots of different rocks forming, depending on the water level and the environment of deposition at the time. Let’s use the skills we’ve learned and interpret the history of a real rock sequence. The picture below is of a rock sequence exposed in a canyon wall. The dashed lines indicate the contacts between the different rock layers. These layers are sedimentary rock layers formed long ago in the same way rocks formed in the previous activities. These rocks have since been exposed by erosion. Specifically, the river that is currently running through the bottom of the canyon eroded these rocks, but it didn’t form them. Lee Limestone Gunner Formation Sarah Sandstone Eliza Shale Here are some distinguishing characteristics of these rock units that might help you identify their environment of deposition. Make sure the environment you choose explains all of the characteristics (fossils included). Note that the rock units are listed in alphabetical order, not chronologic order. Rock Formation Name Sarah Sandstone Characteristics Lots of quartz, well-sorted, fine-grained, animal tracks and wind-blown cross-bedding. (~184 million yrs old) Eliza Shale Contains mudcracks, ripple marks, fern fossils and animal tracks. (~209 million yrs old) Lee Limestone Fossils of freshwater and saltwater shellfish, corals, and sponges (~147 million yrs old) Gunner Formation Sandstone and limestone - fossils of coral, sponges, shark teeth (~162 million yrs old) 63 Lab #3: Sedimentary Rocks and Depositional Environments 1. Fill out the chart on the left by writing the name and likely environment of deposition for this sequence of rocks. Youngest Formation Name One Possible Depositional Environment Lee Limestone Gunner Formation Sarah Sandstone Eliza Shale Oldest 2. Write a geologic history. Use your new-found skills of interpreting sedimentary rocks to describe how this canyon formed. In other words, what events occurred in this location to create each of these rock layers? Include the following: • Age of the formation and depositional environment (based on layer characteristics) • What happened to change the environment over time • How the rocks have been exposed Note #1: The last event should be erosion by the modern river. Note the time difference between the time it took to form these rocks and the time since they were formed. The modern river started flowing around 5 million years ago. Note #2: This question is intended to be challenging. If you get stuck, try consulting your TA during his or her office hours. Please note that writing a geologic history of a sedimentary sequence is the main goal of this lab, so do a good job here. Attach a sheet if you need more room. ________________________________________________________________________________________ _______________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ _________________________________________________________________________________________ ________________________________________________________________________________________ _______________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 64 Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Lab #4: Metamorphic Rocks Lab # 4: Metamorphic Rocks The purpose of today’s lab is to introduce you to metamorphic rocks. By the end of the lab you should be able to distinguish between different metamorphic rock types, identify their potential parent rocks, and determine the pressure and temperature at which they formed. Objectives 1) Understand the processes through which metamorphic rocks form. 2) Be able to identify common metamorphic rocks and interpret their origin based on their texture. 3) Be able to name a possible protolith (parent rock) of a metamorphic rock. 4) Interpret the tectonic setting of various types of metamorphic rocks. 5) Be able to estimate ranges in pressure and temperature of formation for common metamorphic rocks using charts and diagrams. Materials: Pencil (no pens) Textbook Calculator Prelab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook, as well as the web links provided on the Canvas site. The ConcepTest will be on material related to sedimentary rocks from lab 3 and reading material from lab 4 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Metamorphic minerals Activity 2: Metamorphic rocks Activity 3: Rock quiz review Homework Activities (due the beginning of next lab) Activities on pages 76-78 67 Lab #4: Metamorphic Rocks Metamorphic Rocks Metamorphic rocks form when pre-existing rocks (igneous, sedimentary or other metamorphic rocks) are subjected to changes in temperature and pressure, but not high enough temperature to melt the rock (once it melts, it’s an igneous rock). Some examples of metamorphic rocks are: gneiss, schist, phyllite, slate, marble and quartzite (Fig. 1). Figure 1. Examples of metamorphic rocks, gneiss (left) and phyllite (right). Origin of Metamorphic Rocks Metamorphism refers to the changes in the solid state to pre-existing rock, which commonly occurs deep within the lithophere. Metamorphism can involve an increase in pressure (P) or temperature (T), or both. Chemically active fluids also play a role in mobilizing ions to allow metamorphism to take place. The protolith (parent rock) also determines the resultant metamorphic rock. Protoliths may be sedimentary, igneous, or metamorphic rocks of a different grade. The characteristics of the metamorphic rocks indicate the tectonic setting of formation (Fig. 2). Metamorphic conditions can occur in tectonic collision zones, subduction zones, or adjacent to igneous intrusions deep below Earth’s surface (Fig. 3). Characteristics Texture: non-foliated Tectonic Setting Adjacent to igneous intrusions. Type of Metamorphism Usually looks granular (interlocking crystals of one dominant mineral) Increased T, and often hydrothermal (hot) fluids, are the most important agents. Contact Texture: foliated (less commonly granular) Convergent boundaries or collision zones. Foliation types: slaty→phyllitic→schistose→gneissic (see next section for definition) Both tectonic settings cause increase in P and T. Texture: foliated (specifically schistose) Subduction zones at convergent boundaries. Have a specific mineralogy called blueschist (blue minerals formed in high P-low T metamorphism) Cold ocean lithosphere subducts into the hot mantle creating special circumstances of very high P and low T. Regional or Progressive Subduction (blueschist) Figure 2. Metamorphic rock characteristics, tectonic setting, and types of metamorphism. T = temperature, P = pressure. 68 Wet partial melting of the upper mantle Compression causing mountain belts and regional metamorphism Contact Metamorphism (around magma bodies) high T - low P Zone of high pressure/low temperature subduction zone metamorphism Hydrothermal alteration (metamorphism) of ocean floor basalts Lab #4: Metamorphic Rocks Figure 3. Tectonic setting of metamorphic rocks. 69 Lithosphere Lab #4: Metamorphic Rocks Metamorphic Rocks Classification I. Metamorphic Textures Foliation is the diagnostic texture of metamorphic rocks, although not all metamorphic rocks are foliated. Foliation is defined as the parallel or linear alignment of grains in a rock in an interlocking crystalline form (Fig. 4). Most commonly the minerals that align are mica and amphiboles. Non-foliated metamorphic rocks generally display a recrystallized or granular texture (interlocking crystals that are often larger and more intergrown that those in igneous rocks). Protolith Slate Phyllite Schist Gneiss Figure 4. Progression of foliated textures. Degree of foliation is dependent upon the metamorphic grade (see next page). II. Metamorphic Compositions One of the important aspects of metamorphic rocks is that the composition of the rocks stays fairly constant. Unless abundant hydrothermal (hot) fluids are involved, the bulk chemical composition does not change much with metamorphism. Through changes in pressure and temperature, metamorphic rocks change by growing new minerals with the same chemical composition. So, the elements that make up the protolith are the same elements in the metamorphic rock. III. Relationship Between Composition and Texture The amount of pressure and the mineralogy of the rock affect the development of foliation. For example, if the parent rock is composed of one dominant mineral (e.g. limestone or quartz sandstone), the elements in that mineral can not rearrange to become new minerals due to the lack of other elements. In contrast, if a rock made up of numerous minerals, the elements can rearrange to become new minerals such as mica and amphibole, which tend to align and foliate. Metamorphic Minerals The different minerals present tell you a lot about the pressure and temperature of metamorphism, as different minerals will grow at different conditions (refer to Metamorphic Grade section on the next page). Below is a table of some of the common metamorphic minerals. Important Metamorphic Minerals Mineral Diagnostic Mineral Properties Metamorphic Grade Quartz Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage Any Garnet Often dark red, hard (scratches glass), can have conchoidal fracture (break in smooth curves), no cleavage, crystal is 12-sided Medium-high or higher Calcite White, soft (scratched with a knife but not with a fingernail), cleavage in 3 directions (rhombic), reacts (fizzes) with dilute acid Any Mica Brown/translucent, soft (scratches with fingernail), 1 good cleavage (flakes off into thin sheets) Medium-low or higher Actinolite Light to dark green, hard, good cleavage, needle-shaped crystals. A type of amphibole Medium-high or higher Feldspar White/pink/tan, hard (scratches glass), good cleavage in 2 directions High Figure 5. Common metamorphic minerals and their properties. 70 Lab #4: Metamorphic Rocks Metamorphic Grade Not all metamorphic rocks are recrystallized to the same degree. The intensity of metamorphism, called metamorphic grade, depends on how much pressure and heat have been applied. Minerals tend to grow in size with increasing grade. Also, some rocks change into other metamoraphic rocks depending on the grade. However, certain rocks do not change much with increasing metamorphic grade (e.g. marble and quartzite). The chart below (Fig. 6) is an approximate guide to the pressure and temperature ranges for different metamorphic grades. Different metamorphic grades are a result of varying pressure and temperature conditions. To help you with the the visualization of where in the different conditions occur in the lithosphere refer to Fig. 7. Metamorphic Grade Pressure Range Temperature Range Common Foliated Rock Common Non-foliated Rock Low 1-4 kbar 200-325 oC slate quartzite, marble, greenstone, serpentinite Medium-low 1.5-6 kbar 325-450 oC phyllite Medium-high 2.5-12 kbar 450-525 oC schist quartzite, marble, greenstone, serpentinite quartzite, marble, greenstone, serpentinite quartzite, marble, greenstone, serpentinite High 2.5-20 kbar 525-650 oC gneiss quartzite, marble, eclogite, serpentinite Igneous Once a rock melts, it is no longer metamorphic. If only part of the rock melts, the liquid part is magma and the remaining solid part is still high grade metamorphic rock (this kind of rock is called a migmatite) Figure 6. Table of approximate conditions for metamorphic grades. Units of pressure are in kilobars (kbar), where 1 bar is roughly equal to atmospheric pressure, and one kbar is roughly equal to 1,000 times atmospheric pressure. Temperature (oC) 100 200 300 Sedimentary conditions 500 600 700 800 Contact metamorphism mm 1 2 cond Pressure (kilobars) ition s On (mig set of m mat ite f elting orm atio n) mm ade 5 6 ous These conditions are not found in nature 4 Igne 25 Hig 20 3 h gr med iu 15 mh igh mm grade low mm grade ium med Depth (kilometers) 10 low g rade 5 400 7 8 Figure 7. P-T diagram for metamorphic rocks showing the different metamorphic grades. 71 Lab #4: Metamorphic Rocks Classifying Metamorphic Rocks Follow these steps to help you identify metamorphic rocks. Use the chart below to name the rocks. Step 1: Determine whether the rock is foliated or non-foliated (Fig. 4, first column in the chart below). Step 2: Make observations about the texture. Look at the 3rd and 4th columns for suggestions. Are the minerals aligned (foliated) or it the texture random (granular)? Are the rocks shiny? Scaly? Banded? Step 3: Are the minerals big enough to see without a hand lens? Are the minerals big enough to identify? If so, identify them. Check the 4th column to see if they are listed. Step 4: Identify the rock. Look at the 1st column to estimate the metamorphic grade and the 2nd column to identify the protolith. Often grayish-green, (shiny but no crystals) Aligned minerals, (“scaly” texture) Non-Granular (Massive) 72 Figure 8. Metamorphic rock classification chart. Lab #4: Metamorphic Rocks Metamorphic Rocks and Isotherms It is important to understand how pressure and temperature change in the lithosphere. Since the center of the Earth is very hot (hotter than the surface of the sun), the temperature below Earth’s surface quickly rises as depth increases. The rate of temperature change with depth is called the geothermal gradient. The geothermal gradient varies depending where you are on the planet. In some places it is steeper (meaning it gets hotter faster), and in other places is shallower (meaning is doesn’t get hot very quickly with depth). Geothermal Gradient = Temperature (°C) Depth (km) Low grade metamorphism begins to take place at around 200oC. How deep must a rock be in order to reach this temperature? Using a few data points and some clever math to calculate how heat flows through the Earth, we can establish lines of equal temperature, called isotherms (“iso” meaning the same, and “therm” meaning temperature). Isotherms can be flat or bend around cold or hot areas. In general, isotherms tend to be parallel to one another. However, isotherms (and the geothermal gradient) are much more complex where there are inconsistencies within the crust (e.g. a rising magma plume). See Fig. 9 below for a hypothetical isotherm diagram. surface lithosphere o 200 C o 400 C 600 oC 800 oC 1000 oC 1200 oC 1400 oC 200 oC 400 oC magma 600 oC o 800 C o 1000 C 1200 oC 1400 oC asthenosphere Figure 9. Hypothetical isotherm diagram. The surface is room temperature (~20 oC), and the isotherms increase in 200oC increments. Notice how the isotherms curve around the magma chamber. The magma itself ranges in temperature from ~825oC and 1,300oC, based on the isotherms, and the bottom of the magma chamber is hotter than the top. Metamorphism and Plate Tectonics Pressure and temperature conditions vary in different tectonic settings. Also, different rocks types will be present in different tectonic environments, so the protoliths can vary as well. As you examine the rock samples in this lab, keep the following things in mind: • The same parent rock can metamorphose into different metamorphic rocks depending on the grade. • Typically, the grain size and the coarseness of the foliated texture increase with an increased grade. • The type of minerals present in the rock are also clues to the pressure and temperature conditions. Many minerals have very restricted conditions where they are stable. If conditions exceed the stability limit, the mineral will break down and change into another mineral that is stable under the new conditions. The significance: Metamorphic rocks commonly represent the roots of ancient mountains. The intense conditions likely took place deep in a tectonic collision zone, either an ocean-continent convergent boundary or a continentcontinent convergent boundary. These rocks are then exposed at the surface due to uplift and deep erosion. 73 Lab #4: Metamorphic Rocks In-Class Activities Activity 1: Identifying Common Metamorphic Minerals 1. Use Fig. 5 to help you identify the metamorphic mineral samples in tray 1, then fill out the table below. Use the minerals you have identified to answer the questions that follow. Sample # 1 Mineral Name Metamorphic grade (estimated) Best identifying characteristic (shape, reactivity, color, hardness, etc.) 2 3 4 a. Which of these minerals are also common in sedimentary rocks? __________________________________ b. Which of these minerals are also common in igneous rocks? _____________________________________ c. Which of these minerals are unique to metamorphic rocks? ______________________________________ Activity 2: Identifying Common Metamorphic Rocks 1. Use Fig. 8 to identify the samples in tray 2, then fill out the chart on the next page. Sample Foliated or Non-foliated? Metamorphic Rock Name Metamorphic Grade Protolith A B C D E F G H 74 TA CHECK _______________________ Lab #4: Metamorphic Rocks Activity 3: Rock Quiz Review To help you prepare for the rock quiz next week, we have provided samples of 9 rocks that are often misidentified or mistaken for one another. As you are identifying the rocks, recall the processes you went through in the Igneous, Sedimentary, and Metamorphic Rock Labs. a. Use the rock identification sheetfound at the back of your lab manual. b. Distinguish between igneous, sedimentary and metamorphic rocks using their characteristic textures. Key Textures of Igneous, Sedimentary, and Metamorphic Rocks Interlocking crystals Common texture: crystalline Particles cemented together Common texture: clastic Banded minerals Common texture: foliated Rock crystallized from magma Lithification of sediment produced rock Rock subjected to increased pressure & temperature causing parallel alignment of minerals Igneous Sedimentary Metamorphic Description Sample Rock Name Coarse-grained, plutonic, mafic Igneous Fine-grained, volcanic, mafic Fine-grained, volcanic, felsic Fine-grained, volcanic, intermediate Sedimentary Fine-grained, light in color, potential for layers and fossils Very fine-grained, hard (scratches glass), conchoidal fracture Medium-grained, gritty Fine-grained, soft, reacts with diluted acid (HCl) Metamorphic Fine-grained, slightly foliated TA CHECK _______________________ 75 Lab #4: Metamorphic Rocks Homework Activities Activity 1: Metamorphic Grade Use the figure below to answer the following questions. You may also want to refer to Fig. 3 & 6-7. 1. What type of metamorphism occurs at low temperature and high pressure? ____________________________ What letter on the chart corresponds to these conditions? ____________________________________________ 2. Rocks near a magma chamber undergo contact metamorphism at varying temperatures and _______ pressure. What letter on the chart corresponds to contact metamorphism? _______________________________________ 3. Give the rock name that best matches the conditions for each location and the protolith. Location 1: shale protolith ____________________ Location 3: shale protolith ____________________ Location 2: basalt protolith ___________________ Location 4: limestone protolith_________________ 4. If the rock at location 1 continued to be buried to a depth of 10 km and temperatures of 325-425oC, what rock would it become? ___________________________________________________________________________ What changes would occur in the rock as a result? _________________________________________________ 5. If the rock at location 4 were heated to temperatures of 750o C, what rock would it become?______________ What changes would occur in the rock as a result? __________________________________________________ 6. Think back to the various metamorphic rocks you have examined in lab. Why do the rocks with a shale protolith have more noticeable changes with pressure and temperature than those with a quartz sandstone protolith? __________________________________________________________________________________________ __________________________________________________________________________________________ 7. List at least two protoliths that are poor indicators of metamorphic grade?_____________________________ __________________________________________________________________________________________ 76 Lab #4: Metamorphic Rocks Activity 2: Metamorphism and Plate Tectonics 1. Fill in the rock name that corresponds with the appropriate protolith on the diagram below. Consider the metamorphic conditions at each location. The eclogite sample has been done for you. Hint: Keep in mind that although this diagram depicts a subduction zone, it also shows other types of metamorphism. 2. Draw the isotherms on the diagram below (refer to the pre-lab reading). To help you, the 500oC isotherm has been drawn as a dotted line. Note that the isotherm is not a straight line. The cooler subducting lithosphere and the hotter magma cause the isotherm to bend. Hint: All isotherms should behave similarly, so use the 500°C isotherm as a guide. Keep in mind that the coolest magma is >800oC, and the asthenosphere is about 1,300oC. Protolith: sandstone Protolith: shale B Oceanic Geothermal Gradient oceanic crust 200oC oceanic o lithosphere 400 C A Protolith: granite 500 oC 800oC 1000oC magma Protolith: peridotite asthenosphere asthenosphere Protolith: basalt Protolith: basalt Eclogite 77 Lab #4: Metamorphic Rocks 3. The rate at which the temperature increases with depth is called the geothermal gradient. a. When the isotherms are more closely spaced, is the temperature changing more quickly or more slowly? Circle one. b. On the diagram on the previous page there are two vertical lines marked A and B. These lines are of equal length (representing about 50 km on the diagram), but the geothermal gradient of line A is consistant, whereas the geothermal gradient of line B is inconsistant. Calculate the average geothermal gradient for each of these lines. Show your work (no calculations, no credit). Hint: refer to your pre-lab reading for the geothermal gradient formula. Assume that the lines start at the surface at a temperature of 0oC. Use the isotherms you drew to estimate the temperature at the bottom end of the line. Include units (oC/km) Line A: __________________ Line B: __________________ c. Increasing pressure causes rocks to become more dense as they get metamorphosed. Look at where eclogite forms. Do you expect eclogite to be very dense? _________________________________________________ What effect do you think this has on plate tectonics (think about why the plates move)? _________________ ________________________________________________________________________________________ Activity 4: A Comprehensive Review Now that you have seen all three main types of rocks (igneous, sedimentary, metamorphic), think about the characteristics of each group. 1. How can you tell a rock from a mineral? _______________________________________________________ __________________________________________________________________________________________ 2. How can you tell a non-foliated metamorphic rock from a plutonic igneous rock? _____________________ __________________________________________________________________________________________ 3. How can you tell a breccia or a conglomerate from a porphyritic rock?________________________________ __________________________________________________________________________________________ 4. How can you tell a biochemical sedimentary rock from a fine-grained clastic sedimentary rock (e.g. limestone vs. mudstone)? _____________________________________________________________________________ __________________________________________________________________________________________ 78 Lab #5: WWU Campus Geology Tour Lab partners:__________________ ________________________ _____________________________ ________________________ _____________________________ ________________________ Name: __________________________ TA: ____________________________ Day: ___________ Time: __________ Lab #5: WWU Campus Geology Tour Geology encompasses more than landscapes. The materials used to build cars, bikes, roads, buildings, and sidewalks all come from geologic resources, and everything in our daily lives is affected by active geologic processes. We don’t have to go very far to see abundant examples of geologic resources and processes in action. Objectives 1) Go outside and use your geological and analytical skills. 2) Learn interesting information about rocks that you may see every day on campus. 3) Learn about several active geologic processes on our campus. 4) Observe how rocks are used effectively in art and as building materials. Materials Pencil Clipboard Wear appropriate clothes and shoes for going outside. We will go regardless of the weather, so dress for cold and wet if necessary. Prelab work (to be completed before lab begins) Review the Google Earth files provided on the Canvas site under Lab #5 (WWU placemark and the South Bellingham LiDAR overlay). In-Class Activities (due by the end of lab today) Stops are subject to change. Stop 1: Outdoor classroom on Sehome Hill Stop 2: Sehome Hill landslide behind Art Building Stop 3: Fisher Fountain Stop 4: Main library entrance Dark tiles under skybridge Outcrop next to skybridge Stop 5: Memory Walk and Old Main Stop 6: Avalanche victims’ memorial Stop 7: Edens Hall rock sequence Homework Activities (due the beginning of next lab) None 79 Lab #5: WWU Campus Geology Tour Starting point Follow along on this campus map throughout the tour. Clearly label the stop numbers on this map as you go. 80 Lab #5: WWU Campus Geology Tour Stop 1: Sehome Hill Outdoor Classroom 1. Do you think this rock is igneous, sedimentary or metamorphic? ___________________________________ 2. Pay close attention to rock grains and list their characteristics (e.g. size, roundness, sorting)? ______________ _________________________________________________________________________________________ 3. Identify this rock. _________________________________________________________________________ 4. This outcrop is part of the Chuckanut Formation. Based on your observations, make some specific interpretations about the possible depositional environments in which the outcrop in front of you formed. Hint: In other locations, this rock contains plant fossils such as ferns and fronds. _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Stop 2: Sehome Hill Landslide A landslide occurred here in 1961. What evidence can you see that might suggest that there is still a slope stability problem? Look at the sidewalk, the position of the trees, the age of the trees on the landslide and to either side. Check whether there is any water leaking out of the hillside. 1. List and describe three observations below. a. ______________________________________________________________________________________ b. _____________________________________________________________________________________ c. ______________________________________________________________________________________ Stop 3: Fisher Fountain 1. Look carefully at the fountain’s water level (if empty look at the ring left by the water). Based on your observations and the figure below, why do you think the fountain’s water level is uneven? ____________________ _________________________________________________________________________________________ __________________________________________________________________________________________ Ridgeway Dorm WWU Campus Geology Wilson Library Miller Hall Red Square WEST UNCONSOLIDATED SEDIMENT Sehome Hill EAST Dirt brought in for construction and landscaping Peat beds formed in wetlands. Left after the final retreat of glaciers 10,000 year ago. CHUCKANUT FORMATION Sandstone and conglomerate Siltstone, shale, and coal 81 Lab #5: WWU Campus Geology Tour Stop 4: Wilson Library 1. Examine the dark tiles under the skybridge. If you look carefully you will notice rectangular-shaped reflections. These represent cleavage planes of amphibole and pyroxene. a. Do you think this rock is igneous, sedimentary or metamorphic? __________________________________ b. What is the rock texture? _________________________________________________________________ c. What is the rock composition? _____________________________________________________________ d. Identify the rock. _______________________________________________________________________ 2. Examine the rock outcrop next to the skybridge. a. Do you think this rock is igneous, sedimentary or metamorphic? __________________________________ b. Observe the rock layers. What are the black layers composed of? __________________________________ c. Why is there a talus pile accumulated at the base of the outcrop? Explain. ___________________________ ________________________________________________________________________________________ d. This rock should look familiar to you. Where have you seen it before? _____________________________ Stop 5: Memory Walk and Old Main 1. Take a close look at the capsules. Note that older capsules were made from a different rock type than newer capsules. a. What two rock types have been used to make the memory capsules? _______________________________ b. Why do you think they switched? __________________________________________________________ 2. What type of rock makes up the base of Old Main? _______________________________________________ 3. Where do you think the builders got the stone for this part of the building? ____________________________ __________________________________________________________________________________________ Stop 6: Avalanche Victims’ Memorial Six Western Washington University students were killed in an avalanche below the Roman Wall while climbing Mt. Baker. The weather was hot, and the snow conditions were unsafe for climbing that day. 1. Examine the rock. a. Identify the rock. _______________________________________________________________________ b. What geologic process formed these structures? _______________________________________________ Stop 7: Edens Hall In order to put Edens Hall where it is, a portion of Sehome Hill had to be excavated, leaving this exposure of the Chuckanut Formation. This outcrop, unlike the Sehome Hill classroom and the Wilson Library outcrops, contains shale. 1. In the diagram below, list the four rocks we have seen in the Chuckanut Formation in their appropriate box. Swamp Flood plain River 82 Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Lab #6: Streams, Coastlines & Groundwater Lab #6: Streams, Coastlines & Groundwater The purpose of today’s lab is to introduce you to various types of hydrogeological processes. Objectives: 1) Investigate water-related geologic processes. 2) Construct a scale model of a stream, make predictions, and observe stream processes. 3) Construct a scale model of a shoreline, make predictions, and observe shoreline processes. 4) Make observations about groundwater flow. Materials: Pencil (no pens) Colored pencils Ruler Prelab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook. The ConcepTest will be on material related to WWU campus geology from lab 5 and reading material from lab 6 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Streams Activity 2: Coasts Activity 3: Groundwater Homework Activities (due the beginning of next lab) Activities are on pages 93-94 85 Lab #6: Streams, Coastlines & Groundwater Hydrogeologic Processes This lab investigates hydrogeologic processes (geologic process associated with water). Large populations live adjacent to rivers and coastal areas, therefore it is important to understand these environments. We will observe what can happen when humans interfere with natural systems. Streams Streams are dynamic systems that strive for equilibrium. Streams have many changing variables, including discharge, water velocity, sediment load, and base level, which influence stream erosion, transportation, and deposition of material. Stream Characteristics Stream discharge is the volume of water that flows past a given point in a unit of time. Units of measurement influce cubic feet per second (f3/s, CFS) or cubic meters per second (m3/s, CMS). The distance water travels per unit time (how fast water flows) is called stream velocity. Velocity, along with stream width and depth, are used to define stream discharge: Discharge (Q) = Width (W) x Depth (D) x Velocity (V) The body of a stream is called a channel, which will deepen overtime as a result of downcutting. Base level is a stream’s lowest limit of erosion. For streams that flow to the ocean, sea level is the base level. The downhill slope of the stream bed (rise over run) is called the gradient. Streams widen their valleys through erosion and mass wasting of material. As stream channels erode the land they form v-shaped valleys (unlike glaciers, which form u-shaped valleys). Channel Patterns I. Straight Straight streams are rarely found in nature. When straight streams do occur, they are a associated with a steep gradient, a linear zone of weakness (e.g. fault), or are confined inside valley walls in a mountainous region where the stream originates (Fig. 1). II. Braided Braided streams form in areas with highly variable discharge and high sediment load, such as valley outlets. Braided streams deposit sediment in small islands, known as bars, within the stream (Fig. 1). Headwaters Straight stream Braided stream Meandering stream Cut bank Point bar Ocean Water table Alluvial fan Bar Figure 1. Stream types and localities. 86 Delta Flood plain Cut off Oxbow lake Lab #6: Streams, Coastlines & Groundwater III. Meandering Meandering streams form in areas with a low gradient. The outer bends of a meander are the zones of highest velocity and erosion (cut banks), and the inner bends are areas of lowest velocity and deposition (point bars). With time, the cut banks of a meander will touch, causing the stream to flow in a shorter, straighter path (cut off). When this happens, the abandoned meander will form an oxbow lake (Fig. 1). Sediment Transportation and Deposition Streams transport material in loads. There are three types of sediment loads, one being bed load, where sediment is transported through rolling, sliding, and saltation (bouncing) of grains. The suspended load remains lifted by water turbulence . The grain size that can be carried depends on the stream velocity (most suspended load is clay and silt). The third type is dissolved load. This occurs when ions, the products of chemical weathering, are carried in solution. Sediment is not only deposited within the channel. During flooding events, the stream will overflow and deposit mud, silt, and sand on lowlands adjacent to the stream channel, called floodplains. Larger depositional features include alluvial fans, which develop when a mountain stream emerges from a confined canyon onto a wide valley floor, and deltas, which develop when a stream empties into a standing body of water (Fig. 1). Deltas form through foreset bedding (deposition of non-horizontal beds, which results in cross bedding). Coastlines The position of a shoreline moves landward or seaward depending on sea level (rise or fall), tectonic movement (uplift or subsidence), or both. Before understanding the formation and erosion of coastal features, it is important to understand the behavior of waves and sediment transport along a shoreline. Wave refraction: The bending of wave fronts as they approach shallow water near the shore. Longshore current: A current of water that travels parallel to the coast. This occur when waves break on the shore at an angle. Longshore drift: Refers to sediment that is transported parallel to the shore through longshore current. Figure 2. A diagram illustrating coastal landforms. Coastal Structures Since the coast is a high-energy environment, deposition and erosion continuously form a variety of geological features (Fig. 2). Accumulated sand that builds a ridge off a point of land is called a spit. The spit usually points in the direction of sediment transport along a shore. In the instance where a sand spit connects two land masses (e.g. an island and the main land), it is referred to as a tombolo. If a sand ridge builds up to form a bar that closes off a bay from the open ocean, it becomes a baymouth bar. Rocky points of land that protrude seaward, and are often made of resistant rock types, are called headlands. Remnants of eroded headlands are known as sea stacks. When a horizontal bench forms through wave erosion and cliff retreat it is called a wave-cut platform. When a cliff forms through wave erosion and mass wasting, it is called a sea cliff. Sea cliffs occur in regions of high relief. 87 Lab #6: Streams, Coastlines & Groundwater Coastal Disaster Prevention Jetties Seawall Groin The structures listed below are placed to prevent coastal erosion or sedimentation. However, many of these stuructures Breakwater frequently fail due to catastrophic natural events (Fig. 3). Jetties: Walls built to protect harbor entrances from sediment deposition and storm waves. Jetties are often built in pairs. Groins: Structures built perpendicular to the shore. Groins are meant to trap sediment and widen the beach in the up-current direction. Breakwater: Off shore structure built to absorb energy of Figure 3. Various man-made coastal disaster prebreaking waves and provide quiet water near the shore. vention structures. Bulkhead/seawall: Structure built at the base of a slope parallel to the shore. It is designed to protect the shoreline from energy of breaking waves and prevent erosion. Groundwater Groundwater is a critical part of the hydrologic (water) cycle that results from the infiltration of rain or surface water. Water seeps downward through the soil and cracks in rocks to restore the groundwater supply. A recharge area is where water soaks into the ground from the surface (e.g. rainy spots, lakes, etc.). A discharge area is where water leaks out of the groundwater system (e.g. streams, springs, etc.). Groundwater flow rates depend on the porosity and permeability of the subsurface material, as well as the hydraulic gradient (the slope of the water table). Porosity is the volume of pore space in soil, sediment, and rock, and is often reported as percentage (%) of open space in a rock. Permeability is the ability to transmit fluid, and how easy fluids travel through the pore space. Within the subsurface, water concentrations are divided into two zones. The unsaturated zone (vadose zone) is a zone where some pore space is not filled with water. The saturated zone (phreatic zone) is a zone where all the pore spaces are saturated with water. The boundary between the the two zones is called the water table (Fig. 1 and Fig. 4). The water table mimics the topography of the ground surface and therefore can have highs and lows and can be sloped. An aquifer is a porous and permeable layer of sediment or rock from which a useful amount of groundwater can be obtained. An unconfined aquifer is a partially filled aquifer that is open to receive water from the surface. A confined aquifer is an aquifer that is overlain by a low permeability aquitard (a confining layer often made of clay), and is therefore protected from surface contamination. Water in a confined aquifer is under significant pressure. unsaturated zone (vadose zone) well unconfined aquifer well sandstone confined saturated zone (phreatic zone) shale aquifer granite Figure 4. The influence of rock types on groundwater. 88 Lab #6: Streams, Coastlines & Groundwater In-Class Activities In nature, each geologic process has many variables. To successfully model change in real systems, it is important to change only one variable at a time so that you can determine the effect from that change. Keep this in mind when completing this lab. Activity 1: Stream Processes As a class, create a river setting, make predictions, and carry out several experiments to see if your predictions are correct. 1. Create a meandering channel that is at least 4-5 cm deep and wide. Next, 4-5 volunteers can choose a site at which to build a house. a. In the box below, draw a sketch (to scale) of the river and buildings. Label your diagram with a scale bar (the scale of a map or diagram is defined as the ratio of a distance on the map to the corresponding distance on the ground), north arrow, and with the following: HeadwatersPoint bar Meandering channel Delta (will build up over time) Cut bank b. Predict where you think erosion will occur, label places on your drawing with a E for erosion. c. Predict where you think deposition will occur, label places on your drawing with a D for deposition. Symbol Key 89 Lab #6: Streams, Coastlines & Groundwater 2. Make observations about change through time. a. Turn the switch on and allow your river to flow for a few minutes. b. Observe how the stream channel changes with time. Draw these changes on your sketch. Hint: Note where erosion and deposition occur. Also pay attention to the delta, as it will grow over time. c. Describe how the delta (or alluvial fan) grows over time. ________________________________________ ________________________________________________________________________________________________________ d. Assess the properties. Where did the most damage occur (cut bank or point bar)? Where did the least damage occur? __________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 3. Turn off the switch. Place a small block on the outside of one meander bend. This block is meant to serve as a disaster prevention structure to prevent lateral channel erosion. Turn the switch on again. Observe that the block causes rapid erosion in places not protected. a. Observe the changes. What happens close to the structure? _____________________________________ ________________________________________________________________________________________ b. What happens directly downstream on the same bank as the structure? _____________________________ ________________________________________________________________________________________ c. What happens directly downstream from the structure on the opposite bank? _________________________ _________________________________________________________________________________________________________ Activity 2: Coastal Processes 1. Like most geologic processes, coastal processes involve small changes over long period of times. Therefore, we will look at the effect of day-to-day water movement (low wave height, low energy) and storms (high wave height, high energy). a. Measure sediment thickness at the two marked locations. Write measurement on the chalkboard (in cm). b. The TA will take a picture of the coastline prior to the storm stimulation. c. Replicate a storm by increasing the wave height. Let the model run at storm intensity for 2 minutes. d. Remeasure sediment thickness at the two marked locations. e. The TA will take another picture of the coastline after the storm stimulation. To complete your homework activity, refer to these pictures and the collected data, which will be posted on the Canvas page. 2. Where do you think the most erosion and greatest deposition will occur? _____________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 3. In the box below, roughly sketch the coastline and indicate where erosion and deposition occurred. Remember to include a scale bar and a north arrow. Beach side Water side 90 Lab #6: Streams, Coastlines & Groundwater a. When was the most sediment transported? ___________________________________________________ b. Based on your observations, when did the seawall (bricks) prevent erosion? When did they promote erosion? ________________________________________________________________________________ c. Describe how your predictions about erosion and deposition compared to your findings. ______________ ________________________________________________________________________________________ ________________________________________________________________________________________ Activity 3: Groundwater Processes 1. Write the following terms in the appropriate location on the diagram below. Refer to your pre-lab reading (pg. 88) for definitions. recharge areadischarge areawater table confined aquifer unconfined aquifer aquitard vadose (unsaturated) zone phreatic (saturated) zone 2. Describe the shape of the water table of your model. _____________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ well numbers 1 2 3 4 5 6 7 u.s.t lake 8 9 10 11 stream lake stream water water input input water water exit exit 91 Lab #6: Streams, Coastlines & Groundwater 3. For this experiment, read the instructions carefully. a. Have a small syringe with dye, a large syringe with water, a ruler, and a stopwatch ready to use. b. Add one drop of dye to well #6 using the small syringe, then add the contents of the large syringe to the same well (this will help the dye percolate through the sand). c. Time the movement of the dye for one minute. d. At the end of the minute, measure the distance the dye traveled and write down on the space below. Time: 60 seconds Distance: _________________ cm e. Calculate the rate of groundwater flow. Show your calculations and include units. Hint: Groundwater flow = distance ÷ time ___________________ f. What happened to the dye plume as it moved through the sediment?__________________________________ _________________________________________________________________________________________ g. Observe water flowing through the sediment. What determines the flow direction? Refer to your pre-lab reading. __________________________________________________________________________________ h. Now add one drop of dye to well #3 and follow it with water. Does the plume behave differently than it did in well #6? Explain your observations. ____________________________________________________________ _________________________________________________________________________________________ __________________________________________________________________________________________ 4. Reach into the rear of the tank and close the discharge area (turn the green handle 90 degrees either way). Now, open the stream valve. In this exercise, the dye will represent some toxic pesticides or herbicides. a. Make sure the stream is flowing properly. b. Add one drop of dye to well #6 and follow it with a squirt of water. c. What happens to the plume of contamination? _______________________________________________ _______________________________________________________________________________________ d. How does this impact the water table? ______________________________________________________ _______________________________________________________________________________________ e. Add another drop of dye (pollution) to the well. Where does the contamination end up and approximately how long does it take for the water to clear up? __________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ f. If this model represented a real contamination scenario, how would the pollution impact a community who relies on water from this groundwater source? ____________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ g. If you were going to build a house on this model, which well would you want as your drinking water well? Why? __________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ _______________________________________________________________________________________ TA CHECK_________________ 92 Lab #6: Streams, Coastlines & Groundwater Homework Activities Activity 1: Streams 1. Describe the relationship between water velocity and deposition and erosion of sediment. Think of where erosion and deposition occurred in the stream table. _______________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 2. Think back to the In-Class activity and how the placement of structures impacted the stream behavior and vice versa. What factors would be different in the real world? ____________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ Activity 2: Coasts 1. Go to the lab Canvas page and download the pictures and data from the coastal wave experiment. In the space below, use colored pencils to draw the changes is the coastline over the course of the day. a. Draw the coastline in the 8:00 am picture. b. Using a different color, draw the coastline in the final picture. c. Label the north arrow, scale bar, and show the direction of the incoming waves. d. Label coastline features, which may include: headland, lagoon, islands, direction of longshore transport, etc. Beach side Water side 2. Comparing the first and last images, where did the most erosion occur (sediment 1 or sediment 2)? What about deposition? __________________________________________________________________________________ __________________________________________________________________________________________ 3. Now look at the entire sequence of pictures. Describe the changes to the coast line over the course of the day. In particular, compare the erosion and deposition patterns between storms and daily events._________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 93 Lab #6: Streams, Coastlines & Groundwater 4. Look at the measurements of sediment thickness. Plot the results on the graph below, with time on the horizontal axis (the dependent variable) and sediment thickness on the vertical axis (the independent variable). Write the thickness values on the vertical axis. Be sure to plot both sediment 1 and sediment 2. 8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 a. Does sediment 1 thickness increase, decrease, or remain constant over time? What about sediment 2? Explain. ___________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ b. Label storm events on the graph. Activity 3: Groundwater 1. What is the difference between porosity and permeability? _________________________________________ __________________________________________________________________________________________ 3. In many parts of the world, water demands can only be met by pumping groundwater. However, over-pumping of groundwater can result in major problems. For instance, over-pumping groundwater depresses the water table, which in return can alter the direction of water flow. If a wetland (where the water table meets the surface) is adjacent to a town that is over-pumping groundwater, the water can flow from the wetland towards the area of lowered water table, possibly causing the wetlands to dry up. Withdrawls (billion gallons/day) 2. Which sedimentary rocks tend to be more porous? Less porous? ___________________________________ __________________________________________________________________________________________ Rural Industrial Public Supply Irrigation Fresh Groundwater Withdrawls in the US (USGS data) a. Examine the graph to the right. What are two reasons that could be causing the increase in groundwater usage across the US?____________ ________________________________________________________________________________________ b. Come up with and explain two problems that could result from over-pumping groundwater. ___________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 94 Lab partners:__________________ ________________________ Name: __________________________ _____________________________________________________ TA: ____________________________ _____________________________________________________ Day: ___________ Time: __________ ConcepTest Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Question #_____ Initial thoughts: Small Group Answers Additional comments/answers Now that you have completed this week’s lab, consider ConcepTest question #2 for this week. Would you answer the question differently now? Has your understanding of the topic changes now that you’ve worked through these activities? Review what you wrote in the “initial thoughts” box. In the space below, compare your pre-conceptions to what you know now after participating in the lab. Now we’re going to ask for your input on the lab. What was the best part of this lab? This can be the most fun part, the most helpful exercise, or just your favorite thing about the lab. What aspects of this lab were the most confusing to you? Other comments about the lab? Lab #7: Geologic Hazards of Whatcom County Lab #7: Geologic Hazards in Whatcom County Objectives: 1) Learn about some of the natural hazards that exist in Bellingham and Whatcom County. 2) Understand what factors lead to the highest potential for natural hazards. 3) Understand the role of water in natural hazards. 4) Assess Whatcom County’s volcanic hazards. Materials Pencil (no pens) Textbook Prelab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook, as well as the web links provided on the Canvas site. The ConcepTest will be on material related to hydrogeologic processes from lab 6 and reading material from lab 7 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Angle of repose Activity 2: Earthquakes Homework Activities (due the beginning of next lab) Activities on pages 104-105 97 Lab #7: Geologic Hazards of Whatcom County Geologic Hazards of Whatcom County Fundamental Concepts of Natural Hazards Hazards are predictable through science. To successfully predict hazards, scientists study the frequency, distribution patterns, size, and magnitude of past events. The consequences of natural hazards can be minimized. The ability to predict and determine the probability of hazardous events is crucial for risk analysis, and understanding how a natural hazards will affect people, communities, and infrastructure. The same hazardous events that produced disasters in the past are now creating catastrophes. Poor land use, increasing populations, and more expensive building practices are resulting in significantly greater damage from modern hazards in terms of both human and financial losses. In order to reduce the impact of natural hazards, there must be cooperation between scientists, politicians, engineers, land-use planners, and disaster management personnel. Risk vs. Hazard The terms hazard and risk are often used incorrectly. A hazard is the actual phenomenon that will cause damage to people or property. Risk is the likelihood of being affected by a hazard. Therefore, it is important to identify potential hazards for a given area, and equally important to assess the risk for those hazards. Mitigation Mitigation is the effort to lessen the impact of natural disasters on people and property. Mitigation techniques vary for each hazard. Nearly all mitigation plans include an educational component, because even the greatest hazard mitigation plan will fail if no one knows what the hazards are and what should be done when they occur. Examples of mitigation techniques include evacuation routes, engineering, education, and planning ahead. Western Washington Geologic Hazards There are many hazards that pose a risk to residents of Whatcom County. We will be investigating three of these geologic hazards: mass wasting, earthquakes, and volcanoes. Other hazards are very important, and more information can be found at the Whatcom County Division of Emergency Management: http://www.co.whatcom. wa.us/dem/pdf/natural_hazards.pdf . A ng le of Re po se I. Mass Wasting Ground failure and subsequent movement of earth materials downhill is called mass wasting. Mass wasting includes many different types of ground failure, and range from small instantaneous events (e.g. a rock falling off a cliff), to large instantaneous events (e.g. an extensive mass of sediment flowing downhill due to slope failure), to large gradual events (e.g. slow movement of upper soil layers, known as creep). There are several types of mass wasting that have dramatic impacts and occur in numerous regions, the most common being debris flows. Debris flows occur when loose or uncompacted sediment flows turbulently downhill. unconsolidated sediment Figure 1: The angle of repose is the steepest angle a sediment pile can form. Before we can learn to avoid debris flows, we must first understand some important concepts. The most important of these is called the angle of repose, which is steepest angle at which a sloping surface composed of loose, unconsolidated material will remain stable (Fig. 1). Angle of repose only pertains to loose sediment, and varies with the size and shape of the sediment, as well as the amount of fluid present. Slopes gentler than the angle of repose are stable. However, if the angle is increased at all, the sediment fails and slides down slope. 98 Lab #7: Geologic Hazards of Whatcom County II. Earthquakes The origin of an earthquake is call the hypocenter (focus), and the surface point directly above the hypocenter is called the epicenter. Earthquakes are an exceptionally important geologic hazard in the Pacific Northwest since the Juan de Fuca plate subducts beneath the North American plate, resulting in a relatively constant stream of earthquakes. Additionally, as the oceanic lithosphere of the Juan de Fuca plate sinks into the asthenosphere, it compresses from the high pressure and creates deeper earthquakes. Furthermore, the transform boundary of the San Andreas Fault to the south, the extension of the basin-and-range province to the southeast, and the tectonic activity to the northeast all serve to twist and tear the continental crust in the Pacific Northwest. Figure 2. Collapse of I-880 in San Francisco from the M6.9 Loma Prieta Earthquake in 1989 There are many factors that control how much the ground moves during an earthquake. The two most important controls are the amount of energy released from the earthquake (magnitude) and the distance from where the rock actually ruptured. Another crucial factor is the rock that seismic waves pass through. Earthquake waves travel differently through different rock types, and looser, less tightly bound rock or sediment slows down the seismic waves. This will increase the amplitude of the waves, which increase shaking and results in greater damage (Fig. 2). In general, sedimentary rock is less dense and less compacted than igneous or metamorphic rock, and unconsolidated sediment is even less dense and structured than sedimentary rock. One of the biggest problems with unconsolidated sediment is the additional hazards of liquefaction, which occurs when saturated sediment is shaken (Fig. 3). Water trapped in pore space rises to the surface, and as it accumulates, the sediment become less stable and flows like a fluid. Figure 3. Liquefaction causes apartment buildings to sink into the ground during an earthquake in Japan, 1964. 99 Lab #7: Geologic Hazards of Whatcom County III. Volcanoes The driving mechanism for the vast majority of volcanic eruptions is volcanic gases that are trying to escape from the magma. At depth, these gases are dissolved in the magma. But as the magma rises, the pressure that confines the gases in the magma is reduced (decompresses), allowing the gases to form bubbles. As the magma rises, decompression allows more bubbles to form and existing bubbles to expand, which in turn drives the magma to rise and so forth. This positive feedback loop can sometimes lead to an volcanic eruption. There are two major factors that control decompression of magmatic gases. The first is the amount of gas present in the magma. If a magma has a lot of gas, it would be more likely to have an explosive eruption. The second controlling factor is the how fast magma is able to rise and how easily bubbles are able to rise within the magma. The formation of bubbles is controlled by the thickness, or viscosity, of the magma (see Lab #2). Highly viscous magma is very thick and difficult for bubbles to move through, and gases become trapped. Low viscosity magmas are runny and bubbles have an easier time migrating through the liquidrock. Viscosity in magma is controlled by the composition and the temperature of the magma. Felsic magma is much more viscous than mafic magma due to high silica contents and cooler temperatures. Therefore felsic eruptions are more violent than mafic eruptions (e.g. Kilauea vs. Mount St. Helens). Figure 4: The most common volcanic hazards (by USGS). Volcanic Hazards Volcanoes pose many hazards such as lahars (volcanic mudflows; Fig. 5) and volcanic ash (tephra) fall (bits of pulverized rock and glass that are expelled during a volcanic eruption; Fig. 4). Lahars are a mixture of water and loose ash that flow down stream valleys very quickly. Because streams are an important source of water, agriculture, and transportation in most regions of the world, the banks of most streams are densely populated. For this reason lahars are responsible for the most volcano-related fatalities worldwide. Lahars are a common geologic occurrence, and form when loose volcanic material on the flanks of the volcano is washed downstream by a sudden pulse of water. During an explosive volcanic eruption, hot ash causes snow to melt and generate large quantities of water. Once in a river valley, the water is incorporated in the lahar and it is able to pick up more sediment and rock, often until it has the consistency of wet cement. This flood of thick, muddy water (which can travel at speeds exceeding 30 mph) contains much more mass than a normal flood, so it can easily wipe out structures near rivers, like bridges or dams. Lahars can flow great distances, sometimes up to 40 miles, but usually travel less than 25 miles. Figure 5. Mount St. Helens lahar after a small eruption. 100 Lab #7: Geologic Hazards of Whatcom County In-Class Activities Activity 1: Angle of Repose 1. Predict the stability of the materials in your experiment by determining which sediment is most stable and which sediment is least stable. Stability Reason Sediment #1 __________________ ________________________________________________ Sediment #2 __________________ ________________________________________________ 2. Measure the steepest angle you can create with each sediment. a. On your sheet of wax paper, hold the protractor with the bottom edge flat along the bottom of the wax paper so you can read the centimeter scale along the top of the protractor. b. Place the lip of the sample cup on the 3 cm mark of the protractor and gently pour the sediment onto the protractor. You should be making a pile of sediment that is split in half by the protractor. c. Continue pouring the sediment until the slope of the pile reaches the focus point on the protractor (the point from which all the angled lines are radiating). d. Measure the angle of the pile from horizontal and record it below. e. Pour the sediment back into the cup. f. Repeat the above steps for attempts 2 and 3. Sediment #1: Angle of repose for attempt 1 ________ o Angle of repose for attempt 2 ________ o Angle of repose for attempt 3 ________ o Average angle of repose for sediment #1: ________o Sediment #2: Angle of repose for attempt 1 ________ o Angle of repose for attempt 2 ________ o Angle of repose for attempt 3 ________ o Average angle of repose for sediment #2: ________o 3. Which sediment had the greatest angle of repose? How do the results compare to your prediction? _________ __________________________________________________________________________________________ __________________________________________________________________________________________ 4. Use the hand lens to examine each type of sediment. Write down two characteristics about each of the sediments below: Sediment #1: ___________________________________________________ ___________________________________________________ Sediment #2: ___________________________________________________ ___________________________________________________ 5. Consider the differences between the sediments. What sediment characteristics control the angle of repose? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 101 Lab #7: Geologic Hazards of Whatcom County 6. Repeat the experiment for Sediment #3. a. Measure the angle of repose for sediment #3 (dry): _____________________________________________ b. Measure the angle of repose for sediment #3(damp): ____________________________________________ c. Stir the cup containing the saturated sediment. Measure the angle of repose for sediment #3 (saturated): __ ________________________________________________________________________________________ 7. What role does water play in slope stability? ___________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ TA CHECK ______________ Activity 2: Earthquake 1. Creating earthquakes in dry sediment. a. In the cup with dry sediment #3, place the eraser (bulding) on top of the sand with just a little bit of the base buried so it remains stable. b. Below the sediment level, tap the side of the cup with a pencil while rotating the paper (so that the cup spins around while you are tapping). Keep tapping until the eraser falls over. c. Keep track of how many times you tap the cup and write the result below. _________________________ Taps 2. Creating earthquakes in saturated sediment. a. In the cup with saturated sediment #3, bury the cork (underground storage tank) on its side under about 2-3 centimeters of sand. Tip: You might need to add a little bit of water to the sand and stir it up. If standing water is still present on top of the sand after you’ve stirred the sand, pour off the water and stir it up again. b. Place the eraser (building) as you did before, but to the side of the buried cork. c. Repeat the tapping process and carefully observe what happens. _________________________ Taps 2. What happens to the saturated sediment at the surface? ___________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 3. In the saturated cup, why did the building fall over or sink? Did it take more or fewer taps than in dry sediment? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 4. What happened to the underground storage tank? Why? __________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 5. Do you think this would happen if the building were on a more solid rock (e.g. granite)? Why or why not? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 102 Lab #7: Geologic Hazards of Whatcom County 6. Consider your results for the slope stability and the liquefaction experiments. How might earthquakes trigger landslides? ________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 7. Look at the figures below. The top figure is a photograph of the Bellingham waterfront in 1912. The bottom figure is a photograph of the same area in 2010, after the area has been built up. Notice the difference in the location of the shoreline between the two images. Natural sedimentation is too slow to produce such dramatic affects, so this was a man-made change. Sand and mud was dredged from the bottom of Bellingham Bay and placed on the shore to extend the waterfront area. The sediment was not compacted before it was developed into what we see today. a. You have shown that there are hazards associated with building on unconsolidated sediment. Which hazard has the greater risk for the waterfront area of Bellingham, landslide or liquefaction? Why? ________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ TA CHECK ______________ railroad track downtown streets 103 Lab #7: Geologic Hazards of Whatcom County Homework Activities Activity 1: Mass Wasting 1. What would happen to houses built on slopes made of unconsolidated sediments during periods of heavy or prolonged rain? _____________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 2. Vegetation is often used to stabilize slopes prone to failure, and has had mixed results. How does vegetation help stabilize the slope? How might it make the slope more unstable? ________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ Activity 2: Earthquakes 1. The Bellingham Waterfront. Go to Canvas and open Lab7_2-2_BellinghamWaterfront.kmz. Two placemarks are noted in this file, one for the waterfront itself and one for a Bellingham home. Fly around and try to identify the original coastline. Hint: It might help if you increase the vertical exaggeration. You can do so by going to Tools 1 Options 1 3D View tab 1 Terrain 1 Elevation Exaggeration (0.1 - 3, 3 being the highest). a. Which feature helps identify original coastline? ______________________________________________ ________________________________________________________________________________________ b. What street may have been under water in the 1920’s? __________________________________________ Hint: If the road names are not shown, select the Roads checkbox in the Layers panel to the left. c. Which street would have been parallel to the beach in the 1920’s? _________________________________ d. Now look at the Bellingham Waterfront home. This home was for sale for quite some time. The original asking price was $1.2 million. It eventually sold for less than half that price. Although there were likely several reasons for this, describe some possible geologically-based reasons. ________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ Activity 3: Volcanoes 1. Go to Canvas and open Lab7_3-1_MtRuapehu.kmz. This placemark is at the seam between two images, one taken on January 31, 2005 (green) and May 22, 2007 (grayish brown). Notice the differences in the stream valley between these two times. a. What happened during the 28 months between these images? ___________________________________ ________________________________________________________________________________________ b. The deposits from this event are what was left behind when a lahar traveled down Mt. Ruapehu. Given the distribution of the deposits, which path do lahars take (what topographic features control the path of lahars)? ________________________________________________________________________________________ ________________________________________________________________________________________ c. This lahar was moderate in size, but traveled a considerable distance. There was enough force in the lahar to destroy the bridge on Highway 49 (placemarked). How far did the lahar travel before destroying the bridge? Hint: Use the Ruler tool and select Path. Start at the peak and measure the stream path by following the channel as closely as you can. _____________________________ Kilometers d. Lahars are a mix of water, ash, mud, and debris. On a volcano such as Ruapehu, where does the water come from? __________________________________________________________________________________ 104 Lab #7: Geologic Hazards of Whatcom County 2. Go to Canvas and open Lab7_3-2_MSHLahars.kmz and Lab7_3-2_MSHLavas.kmz. a. How does a lahar deposit differ from a lava flow in terms of shape and size? ________________________ ________________________________________________________________________________________ b. Which do you think moves faster, a lava flow or a lahar? Why? ________________________________ ________________________________________________________________________________________ c. Trace the lahar deposits as far as you can. Where do these lahars terminate? _________________________ ________________________________________________________________________________________ d. Use the Ruler tool to measure how far these lahars travelled. _____________________ Kilometers 3. Go to Canvas and open Lab7_3-3_Orting.kmz. Look at the area surrounding the town of Orting. Notice that both rivers pass Orting, joining into one river a few miles downstream (north) along highway 162. a. Trace both rivers upstream back to their source. Which mountain do the two rivers originate from? _____ ________________________________________________________________________________________ b. If that mountain were to erupt, what would happen to the town of Orting? ___________________________ ________________________________________________________________________________________ c. Based on your answer to the previous question, what is the lahar risk level for Orting: low, moderate, or high (circle one)? Explain. ______________________________________________________________________ ________________________________________________________________________________________ 4. Go to Canvas and open Lab7_3-4_Carbonado.kmz. Look at the town of Carbonado, WA, which is upstream along the Carbon River that flows through Orting. a. Is Carbonado further or closer to Mt. Rainier than Orting? _______________________________________ b. Is Carbonado higher or lower elevation than Orting? ____________________________________________ c. What is the lahar risk level for Carbonado: low, moderate, or high (circle one)? Explain. ______________ ________________________________________________________________________________________ ________________________________________________________________________________________ 5. Go to Canvas and open Lab7_3-5_MtBaker.kmz. Examine the area around the volcano. a. If an eruption of Mt. Baker generated a lahar on the northern or western slopes of the mountain, what major highway would the lahar likely damage? _______________________________________________________ b. In which direction would a lahar have to travel to reach Baker Lake? ______________________________ c. If a large lahar were to flow into Baker Lake, what two secondary hazards might exist? Hint: Be sure to examine the south end of Baker Lake. ___________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ d. Go to Canvas and open Lab7_3-5_WhatcomCities.kmz. Assess the lahar risk for each of the cities below (high, moderate, or low) and explain your reasoning. Risk level Reasoning Bellingham: ____________ ______________________________________________________ Ferndale: ______________________________________________________ ____________ Mt. Vernon: __________________________________________________________________ Hamilton: ____________ ______________________________________________________ 105 Lab #7: Geologic Hazards of Whatcom County 106 Lab #8: Geology of Washington Lab partners:__________________ ________________________ _____________________________________________________ _____________________________________________________ Name: __________________________ TA: ____________________________ Day: ___________ Time: __________ Lab #8: Geology of Washington Objectives: 1) Learn about the geologic history of Washington State. 2) Understand how various geologic formation amalgamate. Materials Pencil (no pens) Textbook Prelab work (to be completed before lab begins) Pre-lab activity below In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Geologic time Activity 2: Washington in cross-section Activity 3: Rocks of Washington Homework Activities (due the beginning of next lab) Activities on page 116 Pre-Lab Activity: Key Events in Washington’s Geologic History The activity below replaces this week’s WarmUp Quiz and ConcepTest. In order to receive credit, this activity must be completed before lab. After reading the pre-lab material, list the rock(s) commonly found in each geologic region. Rodinia: __________________________________________________________________________________ Kootenay Arc: _____________________________________________________________________________ Intermontane Superterrane: ___________________________________________________________________ North Cascades Superterrane: _________________________________________________________________ Successor Basins: ___________________________________________________________________________ Olympic Subduction Complex & Crescent Terrane: ________________________________________________ Columbia River Region: ______________________________________________________________________ Cascade Volcanic & Plutonic Arc: ______________________________________________________________ Region formerly covered by Cordilleran Ice Sheet: _________________________________________________ 107 Lab #8: Geology of Washington Geologic History of Washington State Region 1: Rodinia Only the northeastern part of Washington State has been around long enough to be called a native part of North America, all of the rest of Washington consists of foreign imports that formed some place else and were added to North America during the past 200 million years. The eastern part of Washington State is a remnant of a supercontinent called Rodinia that formed ~1.1 billion years, and began to split up by ~750 million years ago. The separate fragments of Rodinia are now dispersed throughout the world. Reconstructions are a bit uncertain but during the Late Precambrian it seems that Washington State was connected to either Siberia or Antarctica (Fig. 1). The remnants of Rodinia that make up northeastern Washington is continental crust, which is generally composed of granite. Pacific Northwest Figure 1. World map showing one possible reconstruction of the Rodinia Supercontinent (750 Ma). Region 2: Kootenay Arc The Kootenay Arc is a thick wedge of sedimentary and volcanic rocks that accumulated near the continental margin of North America between ~550-250 million years ago. It consists of sandstones, conglomerates, lava flows, and pyroclastic rocks that are typically formed along subduction zones (Fig. 2). The arc formed very close to the margin of North America, and was swept up to become part of the continent by the Intermontane Superterrane (Region 3) as it collided with North America about 160 million years ago. Subduction zone Fore arc Farallon Plate Figure 2. An illustration of a subduction zone. 108 Volcanic arc North American Plate Lab #8: Geology of Washington Region 3: Intermontane Superterrane The Intermontane Superterrane is a huge block of rock that accreted to (“docked with”) the western margin of North America ~160 million years ago. In Washington, these rocks include the Kootenay Arc and extend to about the middle of the state, which would have been the Pacific coastline at that time. This superterrane consisted of a volcanic island arc (with andesitic magma) and marine sedimentary rocks (limestone) with fossils from the Tethyan Ocean. The Tethyan Ocean is an ancient ocean near Asia, which means that some terranes found in the Pacific Northwest travelled great distances. The Intermontane Superterrane also includes serpentinized ultramafic rocks brought up from the mantle (serpentine), as well as granitic plutons. After the various terranes joined to form the superterrane, they were covered with sediments that became conglomerate, sandstone and shale. Region 4: North Cascades Superterrane The North Cascades Superterrane extends from the Methow Valley to the San Juan Islands and includes at least 10 separate terranes (crustal fragments from tectonic plates; Fig. 3). Some of these terranes represented volcanic island arcs, others were submarine fans consisting of sandstone, conglomerate, and shale, and other terranes were formed of ocean-floor basalt. This block of terranes docked with North America ~90 million years ago producing deformation, metamorphism, and igneous intrusions throughout the North Cascades. The increased pressure and temperature due to the collision caused parent rocks within the terranes to metamorphose to phyllite, schist, and gneiss (depending on the location and the parent rock). Granite plutons intruded the region between 90-65 Ma. Figure 3. A map showing the different terranes that make up the North Cascades Superterrane. Image source: Geology of the Noth Cascades, A Mountain Mosaic by Tabor and Haugerud. 109 Lab #8: Geology of Washington Region 5: Successor Basin Roughly 60 million years ago, after the major terranes had been added to the margin of North America, the landscape was gradually leveled to a broad flat plain by erosion (similar to Mississippi today). Big river systems flowed westward across this plain, which was gradually sinking, depositing layers of river cobbles/gravel, sand, mud, and abundant plant material (Fig. 4). The total thickness of these deposits exceeded thousands of meters and were eventually lithified into conglomerates, sandstones, siltstones, shales, and coal. The rocks that make up the Chuckanut Mountains near Bellingham, the Peshastin Pinnacles in the Wenatchee Valley, and the fossil-rich rocks around Republic are good examples of these rocks. This deposition continued until ~50 million years ago. Tree Fern Dawn Redwood Cinnamon Tree Sassafras Palm trunk Sycamore Swamp Cypress Palm fronds Figure 4. Fossils commonly found in the Chuckanut Formation near Bellingham, WA. Think about what the presence of plants such as palm trees indicates about the climate at the time of deposition. 110 Lab #8: Geology of Washington Region 6: Olympic Subduction Complex During the deposition of the Successor Basin sediments, a major segment of the outer coast of Washington State was being rifted northward. This resulted in a huge sinking basin along the coastline that was filled with sediments, resulting in feldspar-rich lithic sandstone and shales. Soon thereafter an immense eruption of basaltic lava created big volcanic islands that grew along the coast of Washington and Oregon. As the Cascadia subduction zone (the modern subduction zone) developed, these rocks were pushed up into a horseshoe shaped dome that currently makes up the Olympic Mountains. Great wedges of sea-floor sediments were scraped off the descending plate to become the western part of the Olympics. These rocks are called the Olympic Subduction Complex (Fig. 5). The oceanic sediment (limestone and shale) and ocean floor (basalt) metamorphosed during continued subduction to form marble, greenstone and slate. Figure 5. Map of the Crescent basalts and Olympic Subduction Complex. Region 7: Columbia River Basalts About 17 million years ago a series of rifts appeared in southeastern Washington. From these rifts an immense amount of basalt was erupted. The source of this basalt may have been the Yellowstone hotspot plume. Some of the flows extended all the way from Central Washington (Yakima) to the Washington coast (Astoria) (Fig. 6). In places these basalts accumulated and are more than 3,000 meters thick, and cover an area of more than 170,000 km2 . Most of the flows (96%) were erupted between 17-14.5 million years ago, but the youngest flows are only 6 million years old. The Columbia River Basalts are one of the largest preserved outpourings of lava in the history of the earth. Figure 6. Distribution of the Columbia River Basalts (shown in gray). 111 Lab #8: Geology of Washington Region 8: Cascades Volcanic and Plutonic Arc About 40 million years ago, the Cascadia Subduction Zone developed off the coast between Northern California and British Columbia. Great magma chambers formed as the sea floor of the Juan de Fuca plate was subducted to depths of 90-100 km beneath the western margin of North America. As the magma moved upward towards the surface, most of it crystallized deep underground as plutons of granitic rock. Some magma made it all the way to the surface, producing rhyolitic and andesitic lava and pyroclastic flows. Figure 7. Cascade Volcanic Arc and subduction of the Juan de Fuca Plate beneath the North America Plate. The Cascade Arc has been active for ~40 million years. Older mountains have since eroded, and new mountains are being formed. The current Cascade range began uplift ~14 million years ago. Mt. Baker, Glacier Peak, Mt. Rainier, Mt. Adams, and Mt. St. Helens are the youngest volcanic peaks in Washington State (formation started ~700 million years ago). More than a dozen major volcanic peaks in British Columbia, Oregon and California also exist. Hundreds of deeply eroded, older volcanoes are still present. Region 9: Cordilleran Ice Sheet and Glacial Lake Missoula During the last 2 million years, continental glaciers have covered parts of Washington State at least 6 times. The most extensive ice sheet developed during the most recent event called Fraser Glaciation between ~20,000-11,000 years ago. The Cordilleran Ice Sheet map shows the maximum of this advance ~15,000 years ago (Fig. 8). During this time the glacier covered the Puget Lowlands and most of the northern part of Eastern Washington. The WWU campus was buried well over a mile deep in ice. These glaciers carried large quantities of sediment within the ice. The glaciation also eroded and carved much of the landscape in the Puget Sound Area. In western Montana, on several occasions, a lobe of ice created a temporary dam on the Clark Fork River that produced temporary lakes up to 1000 feet deep. Location of ice dam The ice sheet began to rapidly melt about 13,000 years ago, depositing the unsorted glacial till sediment that the glaciers once carried. In eastern Washington, a series of colossal floods occurred as water trapped by the ice dams broke and ancient Lake Missoula was periodically released. There is evidence that walls of water as much as 900 feet high surged across Eastern Washington, eroding the landscape all the way down to the basalt bedrock. Figure 8. Map of the Cordilleran Ice Sheet and the Missoula floods. 112 Lab #8: Geology of Washington In-Class Activities Activity 1: Geologic Timeline of Washington The purpose of this activity is to reconstruct Washington’s geologic history step by step using the information provided in this lab and your flip book. It is customary to list geologic events with the oldest event at the bottom and the most recent (youngest) at the top. More events have occurred in Washington’s geologic history than are discussed in this lab, but you only need to list the events included in this lab 1.8 13,000 yrs ago: _________________________________________ 15,000 yrs ago: _________________________________________ 20,000-11,000 yrs ago: ___________________________________ 700,000 yrs ago: ________________________________________ 2 mya: continental glaciation begins, covering parts of WA ~6 times 17-6 mya: ______________________________________________ 14 mya: Current Cascade range begins to be uplifted 40 mya: Cascadia subduction zone forms & Cascade Arc becomes active 60-50 mya: ___________________________________________ & ____________________________________________ 90 mya: _______________________________________________ 160 mya: _____________________ & ______________________ collide into North America (terrane accretion) 550-250 mya: ________________________________________ 750 mya: ______________________________________________ 1100 mya: _____________________________________________ TA CHECK_________________ 113 Lab #8: Geology of Washington Activity 2: Cross-Section of Washington In this activity you will use the geographical locations provided by your flip book, as well as the historical order of events from Activity 1, to create a cross-section of Washington. 1. Fill in the blanks for each terrane, volcanic arc, or depositional basin using the names in your lab manual. Think of the geographic distribution on your map and principles of relative dating when making decisions about where each piece belongs. GEOLOGIC CROSS-SECTION OF WASHINGTON W E North Cascades Olympic Mts. Pacific Ocean Puget Sound Present day subducting Juan de Fuca plate CRUST MANTLE 2. What rock type erupted in flows in the Columbia River region about 17 million years ago? ______________ __________________________________________________________________________________________ 3. Does this rock type make sense based on our tectonic setting? What type of volcanic rock or magma usually forms in a continental-oceanic subduction zone such as ours? Explain. __________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ 4. According to the lab manual, what is a possible explanation for the eruptions of mafic magma that formed 17 million years ago in the Columbia River region? __________________________________________________ __________________________________________________________________________________________ TA CHECK_________________ 114 Lab #8: Geology of Washington Activity 3: Rocks of Washington This activity will provide an excellent review of the rocks for the final exam as well as helping you learn to recognize the rocks you will see around our state. Each tray of rocks you identify will represent the rocks found in one of the terranes, arcs, basin or other geologic features of Washington. For each tray, identify each of the rocks, list the rock name(s) associated with each tectonic setting or depositional environment, and list the geologic region to which that rock assemblage belongs. Hint: As you are identifying the rocks, recall the processes you went through in the Igneous, Sedimentary, and Metamorphic Rock Labs. • Distinguish between igneous, sedimentary and metamorphic rocks using their characteristic textures. • Use the rock identification charts to name the rock samples based on their composition and texture. Rock Tray A Rock Identification What rocks are commonly found in this geologic region? Geologic Region of Washington Volcanic islands on the coast: Sediments deposited in offshore basin: Subduction-related metamorphic rocks: B Ancient continental crust (craton): C Sediments eroded from mountains after terrane accretion stopped: D Collision-related metamorphic rocks: Intruded plutons: Submarine fan sediments: E Igneous flows from rifts: F Subduction-related volcanic rocks: Sediments derived from volcanic arc: G Arc volcanic rocks: Intruded plutons: H Sediment deposited: Bedrock exposed by erosion: I Volcanic island arc: Marine sediments: Metamorphosed mantle rocks: Intruded plutons: Sediments that covered terrane: TA CHECK_________________ 115 Lab #8: Geology of Washington Homework Activities Understanding Geologic Maps The different rocks of the various terranes you have explored in today’s lab are spread out around Washington State. To create a geologic map of Washington, geologists explored the entire state and determined the location, type, and age of all the rocks, as well as other significant geologic features. Instead of having to go out and find the rocks ourselves, we can use this geologic map to interpret where those different terranes and rocks are found today. Activity 1: Basic Map Reading Colors are used to differentiate rock units on geologic maps, and each map has a slightly different color scheme. Refer to the map legend to determine the name and age of each rock unit. Hint: Notice that there are five major groups. Each group uses a different color to distinguish it from the others, and the units within each group use different shades of that base color. 1. Name the major groups. ____________________________________________________________________ __________________________________________________________________________________________ 2. What do the labels mean (e.g. Tertiary, Mesozoic, etc.)? ___________________________________________ __________________________________________________________________________________________ 3. Within each group, can you tell which rocks are older and which are younger? Use the geologic time scale to interpret the relative age. _______________________________________________________________________ __________________________________________________________________________________________ Activity 2: Using the Legend and Locating Rocks 1. a. From the legend, what is the abbreviation for the Columbia River Basalts? ____________________________ b. What does each letter in that abbreviation stand for? ____________________________________________ c. Which quadrant of the map (NW, NE, SW, or SE) is dominated by this rock type? ____________________ 2. a. What is the abbreviation for the other rock type that also commonly occurs in this area? ________________ Hint: Its map unit color is beige. b. Which is older, the beige unit or the Columbia River Basalts? Explain your reasoning. _________________ ________________________________________________________________________________________ c. Look at the description of the beige unit in the legend. This unit is associated with the terrane discussed on page 112. What event do you think deposited this unit? Explain. ___________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 3. In which region (W-SW, N-NE, or S-SE) are the oldest rocks (Precambrian and Paleozoic) found? _____________ 4. Find the pre-Cretaceous metamorphic rocks (light purple) and Mesozoic intrusive rocks (pink). a. There are two solid black lines running through these units. Which tectonic feature do these lines represent? ________________________________________________________________________________________ b. To which terrane do the these unit belong? Use their age as well as their rock type to decide. ____________ ________________________________________________________________________________________ c. Two geologic processes have combined to help expose these old rocks at the surface. What are they? ______ ________________________________________________________________________________________ 116 Lab #9: Comprehensive Lab Quiz Lab #1: Plate Tectonics • Understand how the plates move relative to one another. • Know how to draw the 3 different plate boundary types and all associated geologic features. • For each boundary type, be able to describe the patterns of earthquakes, volcanoes, sea floor ages, and topographic features a on a map (review specialty maps in Lab #1). • Be able to calculate how many kilometers a plate has moved in a give number of years (given a rate). Rock Cycle • Understand the processes that can change one rock type into another. Lab #2: Igneous Rocks • Be able to identify important igneous minerals. • Be able to use rock texture and composition to identify igneous rocks. • Understand how grain-size relates to cooling rate in an igneous rock. • Understand which igneous rocks form at different tectonic settings (mantle, hot spot, convergent boundaries, divergent boundaries, etc.). Lab #3: Sedimentary Rocks and Depositional Environments • Be able to identify important sedimentary minerals. • Be able to use rock texture and composition to identify sedimentary rocks. • Be able to determine the possible depositional environments of various sedimentary rocks. • Be able to write a basic geologic history based on a sequence of sedimentary rocks. Lab #4: Metamorphic Rocks • Be able to identify important metamorphic minerals. • Be able to use rock texture and composition to identify metamorphic rocks. • Be able to identify an appropriate parent rock (protolith) for a given metamorphic rock. • Know the different types of metamorphism and their pressure/temperature conditions. • Know how to draw isotherms. • Be able to calculate a geothermal gradient. Lab #5: Campus Tour • Know the rock types and depositional environment of the Chuckanut Formation. Lab #6: Streams, Coastlines and Groundwater • Be able to recognize and name stream and coastal features. • Know the difference between permeability and porosity. • Know the difference between an aquifer and an aquitard. • Be able to show and describe groundwater flow direction and contamination paths on a given diagram. Lab #7: Geologic Hazards of Whatcom County • Be able to explain the difference between risk and hazard. • Understand mitigation and its importance. • Understand how the angle of repose and water contents affect slope stability. • Understand the relationship between earthquakes, liquefaction, and mass wasting. • Understand lahars and their implications. Lab 8: Geology of Washington • Know what kind of events (terrane accretion/mountain building, flood basalts, glaciation, volcanism, etc.) shaped the geology and topography of Washington. • Be able to name at least 5 different rocks that you might find in Washington. • Be able to read and interpret a geologic map. 117 118 Rock Identification Charts Figure 1. Igneous rocks ID chart. Figure 2. Metamorphic rocks ID chart. often grayish-green, aligned minerals, Non-Granular (Massive) 119 Figure 3. Sedimentary rocks ID chart. Clastic rocks can have fossils! (i.e. fossiliferous sandstone or fossiliferous shale) 120 Mineral Identification Tables Important Igneous Minerals Mineral Diagnostic Mineral Properties Composition Quartz Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage Felsic Amphibole/ Pyroxene Brown/translucent, soft (scratches with fingernail), 1 good cleavage (flakes off into thin sheets) White/pink/tan, hard (scratches glass), good cleavage in 2 directions Dark (black or greenish gray), hard (scratches glass), good cleavage Olivine Green (weathers to orange), hard (scratches glass), no cleavage Mica Feldspar Mafic Important Sedimentary Minerals Mineral Quartz Gypsum Calcite Halite Limonite Feldspar Diagnostic Mineral Properties Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage White (can be almost clear), soft (can be easily scratched with a fingernail), good cleavage in 2 directions (but not at 90o) White, crystals can be rhombic, reacts (fizzes) with dilutes acid (HCl), soft (scratched with a glass but not with a fingernail) White or translucent, soft, 3 cleavage planes (cubic crystals), salty taste (taste at your own risk!) Yellow-orange, soft, amorphous (no constant or regular shape) White/pink/tan, hard (scratches glass), good cleavage in 2 directions Important Metamorphic Minerals Mineral Quartz Garnet Calcite Mica Actinolite Feldspar Diagnostic Mineral Properties Many colors (often dull, sometimes translucent), hard (scratches glass), conchoidal fracture (can break in smooth curves), no cleavage Often dark red, hard (scratches glass), can have conchoidal fracture (break in smooth curves), no cleavage, crystal is 12-sided White, soft (scratched with a knife but not with a fingernail), cleavage in 3 directions (rhombic), reacts (fizzes) with dilute acid Brown/translucent, soft (scratches with fingernail), 1 good cleavage (flakes off into thin sheets) Light to dark green, hard, good cleavage, needle-shaped crystals. A type of amphibole White/pink/tan, hard (scratches glass), good cleavage in 2 directions Metamorphic Grade Any Medium-high or higher Any Medium-low or higher Medium-high or higher High 121