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Peanut Butter and Jelly Geology A Study of Faults and Geologic Activity Over ervview California’s diverse landscape and complex geology can be attributed to tectonic faulting. Earthquakes, volcanoes, erosion, uplift--all have played a role in shaping our landscape. In this activity students explore the connections between the topography of the Bay Area and the geological processes that underlie it. They will learn about sediment types, plate tectonics, and how they affect the topography of the Bay Area and its surrounding landscape. Estimated Time 1 hour Objectives Students will be able to: • Describe various faults and their movements • Define and describe plate tectonics • Explain folding and faulting forces of various plate boundaries and their impacts on the geology of the Bay • • • 1 clear plastic straw 1 plastic knife 1 small paper cup of mixture of food items such as raisins, oats, cereal, etc. (optional) Vocabular ocabularyy Blocks, core, crust, fault, normal fault, strike-slip fault, graben fault, subduction, plate tectonics, rocks, sediments, core sampling Materials Part I: Introduction to Geology For each student • 1 oreo cookie • 1 napkin California Science Content Standards Part II: Plate Tectonics and Peanut Butter Make groups of 4-5 students, for each group • 1 copy of the Student Pages of Peanut Butter and Jelly Geology for each student • 1 small paper cup of peanut butter • 1 small paper cup of jelly • 4 slices of bread • 1 flat paper plate Grade 7 Grade 6 Standard Set 1.e: major geologic events, such as earthquakes, volcanic eruptions, and mountain building result from plate motions. Standard Set 1.f: how to explain major features of California geology in terms of plate tectonics (including mountains, faults, volcanoes). 68 Save The Bay’s San Francisco Bay Watershed Curriculum Standard Set 4.a: Earth processes today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time. Grade 7 (continued) Standard Set 4.c: the rock cycle includes the formation of new sediment and rocks. Rocks are often found in layers with the oldest generally on the bottom. Standard Set 4.f: how movements of the Earth’s continental and oceanic plates through time, with associated changes in climate and geographical connections, have affected the past and present distribution of organisms. Grades 9-12 Earth Sciences Standard Set 9.a: the resources of major economic importance in California and their relation to California’s geology. best places to observe faults are usually in roadcuts, quarries, and sea cliff exposures. Fault Classification Faults and fault zones are classified by how the rocks on each side of the fault or fault zone move past each other. There are two main types of movement along faults: 1) a sideways movement called strike slip, and 2) an up or down movement called dip slip. Strike-Slip Faults The movement along a strike-slip fault is approximately parallel to the strike of the fault, meaning the rocks move past each other horizontally. Additional Resources This activity was adapted from “Estuarine Encounters” by Friends of the San Francisco Estuary. http://www.abag.ca.gov/bayarea/sfep/programs/ested/ index.html#estenc USGS Quake Info http://quake.wr.usgs.gov/ Kids GeoZone http://www.consrv.ca.gov/CGS/information/ kids_geozone/index.htm Paper Models from USGS http://interactive2.usgs.gov/learningweb/teachers/ paper_models.htm Background A fault is a fracture along which there is movement. Some faults are actually composed of several fractures called fault branches. Collectively the branches are a fault zone. (see map on front page of activity) California’s diverse landscape and complex geology can be attributed to faulting. Many of the State’s valleys, mountain ranges, and desert areas show the effects of faulting. Faults create underground traps in which valuable reservoirs of petroleum form, and spaces in which underground waters deposit valuable metals in the form of veins and masses of ore. Faults are distinguished by abrupt changes in rock structure or composition. Sometimes a fault can be recognized by the displacement of a particular feature such as a bed or a vein. The The San Andreas is a strike-slip fault that has displaced rocks hundreds of miles. As a result of horizontal movement along the fault, rocks of vastly different age and composition have been placed side by side. The San Andreas fault is a fault zone rather than a single fault, and movement may occur along any of the many fault surfaces in the zone. The surface effects of the San Andreas fault zone can be observed for over 600 miles (1,000 km). Dip-Slip Faults Dip-slip faults are faults on which the movement is parallel to the dip of the fault surface. Normal faults are dip-slip faults on which the hanging wall (the rocks above the fault surface) move down relative to the footwall (the rocks below the fault surface). Normal faults are the result of tension (forces that pull rocks apart). Where the dip of a normal fault’s surface is steep, it is called a high-angle normal fault, or simply a normal fault. The Owens Valley and the Sierra Nevada fault zones are examples of high-angle normal faults. Together they produce a down-dropped block which forms the Owens Valley. This type of fault-bounded valley is called a graben. A fault-bounded ridge is called a horst. Save The Bay’s San Francisco Bay Watershed Curriculum 69 The Sierra Madre fault zone of southern California is an example of reverse-fault movement. There the rocks of the San Gabriel Mountains are being pushed up and over the rocks of the San Fernando and San Gabriel valleys. Movement on the Sierra Madre fault zone is part of the process that created the San Gabriel Mountains. Where the dip of a normal fault’s surface is very gentle or almost flat, it is referred to as a detachment fault or low-angle normal fault. Detachment faults are common in the desert areas of California. Reverse faults are dip-slip faults in which the hanging wall moves up relative to the footwall. Reverse faults are the result of compression (forces that push rocks together). A thrust fault is a reverse fault with a gentlydipping fault surface. Thrust faults are very common in the Klamath Mountains of northern California. Notes The terms normal and reverse were first used by English coal miners to describe faults. When working a flat coal bed where it was dislocated by a normal fault, the miners continued the workings either upward or downward on the fault surface in the same, or normal, direction. The workings in a seam dislocated by a reverse fault were also continued upward or downward on the fault, but in the opposite, or reverse, direction (Ojakangas, 1991). The terms hanging wall and footwall are also old mining terms. These terms were originally used in inclined underground passageways to refer to the rock “hanging” overhead (the hanging wall) and the floor beneath the miners’ feet (the footwall) (Ojakangas, 1991). This background information was taken from the California Conservation web site at http://www.consrv.ca.gov/cgs/information/publications/teacher_features/faults.htm 70 Save The Bay’s San Francisco Bay Watershed Curriculum Teacher PPrroc edur ocedur eduree Par oduction to Geolog artt I: Intr Introduction Geologyy (cream side up) and slowly push it below the other piece of cookie so that the cream scrapes onto the top cookie piece. 1. You can start off by asking the students some simple questions: • Do you know how landscape around the Bay such as mountains is formed? • What is a fault? • Have you ever heard of the term plate tectonics? Do you know what it means? 9. Now let your class try it. 2. Tell your students that they will be using everyday items to represent the earth and explore how natural forces alter and shape the geology of the San Francisco Bay and its surrounding landscape. Their model will help them answer these questions about earth science. 10. Tell the class that the process of one plate sliding beneath another is called subduction and that much of the land around the Estuary is composed of rocks that were altered during subduction. This mixture of rocks that were formed from a scraping of the plates and from subduction make up the bedrock found around much of the Estuary. 11. Explain that although subduction no longer affects the geology of the Bay Area, it affects other areas in the world, and often leads to volcanoes and tsunamis. 3. Pass out one oreo cookie to each student. 12. Now let your class eat the cookies! 4. Tell the students to carefully twist off the top part of the cookie so that they have the two pieces separated and one piece has all of the cream on it. 5. Demonstrate this procedure to the class. 6. Explain to them that they are going to pretend that these two pieces of cookies are tectonic plates of the Earth and that they are going to study the movement of these plates and how they changed the sediments and geology in the Bay Area. 7. Tell them that the process they are going to learn is called subduction and it occurs when one plate moves under the other and the top plate scrapes sediments off the bottom plate while the bottom plate is diving under. 8. Demonstrate the process of subduction while explaining that the Earth’s plates have different types of movements that create different types of structures. Take the oreo cookie with the cream on top Par te T ectonics and PPeanut eanut B utter artt II: Pla Plate Tectonics Butter 1. Tell your class that they are going to perform another experiment to help demonstrate other ways that plates and faults move and learn how that has shaped the Bay. Divide the students into groups of 4 or 5. 2. Pass out the materials and the student pages to each group. (The following directions are also on the student pages). Assist the students as they follow their written instructions and ask discussion questions. 3. Each group will start by spreading peanut butter on two bread slices and jelly on the other two slices (without joining the slices together). *Optional: Students can also add small foods like raisins, oats, cereal, etc. to represent different rocks and minerals. 4. When all the groups are ready, instruct the students to put their sandwiches together Save The Bay’s San Francisco Bay Watershed Curriculum 71 by alternating peanut butter and jelly slices (plain bread sides facing out). 5. Explain to the students that the stack is the bottom of the Pacific Ocean long ago, and that the stack represents the different layers of sediment that have accumulated over thousands of years. 6. Explain the theory of plate tectonics, that the Earth’s crust is made up of 12 different plates that move against each other. The boundaries of these plates is where rock deformation occurs. Tell the class that they are going to use their stack to help them visualize some of the effects of plate tectonics. 7. Ask “What happens to rocks when they are exposed over time to pressure and heat?” Explain that as the ocean floor sediments were scraped against the continent, pressure and heat caused the rocks to metamorphose/deform. Also that deformations occur along plate boundaries. Introduce this concept of folding and faulting due to heat and pressure. 8. Tell them to demonstrate this by applying compressional pressure to the outsides of the sandwich stack, causing the stack to fold and buckle, creating small ridges and valleys. The Student Pages contain a diagram illustrating this and explaining it to the students. This process created many mountain ranges around the world. 9. Now have the students cut their sandwich stacks in half lengthwise. They can demonstrate the strike-slip movement between two blocks by sliding the two blocks towards each other and then horizontal to each other, following the diagrams in their Fault Activity Demo Sheet. The San Andreas Fault has this type of motion. 10. Next the students should cut one of the halves of their sandwich stack in half again, creating two blocks. They can use these to demonstrate a normal fault by pushing the two blocks against each other and having one block slide downwards against the other(normal fault). Then have one slide upwards against the other (reverse fault). The Owens Valley and Sierra Nevada fault zones are examples of normal faults. The Sierra Madre fault zone is an example of a reverse fault movement. 11. The graben fault is a special type of normal fault. The graben fault can be shown by cutting the remaining sandwich stack into thirds and exerting force on the outer thirds to push the inner third downward. Point out which sections are the graben and horst. 12. Now show your students a core sample by taking a clear straw and inserting it carefully through the stack of bread slices. Twist the straw as you insert it into the densest part of the sandwich. After removing the straw, discuss the profile, showing the pattern of materials (the alternating layers of peanut butter and jelly represent the different layers of rock). 13. Explain how the stratified sediments represent the layers of sedimentary rock that were scraped off from the ocean bottom to the continental margin, then moved, through faulting and folding to their present locations around the Estuary. Some of these rocks deposited along the coast of California and created the Coastal Mountain range. 14. Have them take a core sample of their stacks. 15. Discuss with your students that rock layers are laid down horizontally. Let the groups discuss which layers in their model are the oldest and youngest layers of rock. Review 72 Save The Bay’s San Francisco Bay Watershed Curriculum their answers and teach them that “If rock layers are not disturbed the oldest layers are on the bottom and the youngest layers are on the top.” Explain to them that this helps geologists chronologically date rock layers and formations. Clas sion/W rap Up lasss Discus Discussion/W sion/Wrap 1. Begin a discussion that summarizes what has occurred. Review: • • • • Subduction and how it forms new earth How faults and plate boundaries create mountains and valleys The differences between the 3 faults we studied Significance of core samples and what they teach us 2. Divide the sandwiches and serve. 3. You can build paper fault models with your class as well. Research the “Mapping Our Faultlines” Activity on the USGS web site from USGS Learning Web, U.S. Department of Interior, U.S. Geological Survey, Reston, VA. USA. http://www.usgs.gov/education/ Save The Bay’s San Francisco Bay Watershed Curriculum 73 Peanut Butter and Jelly Geology A Study of Faults and Geologic Activity INTRODUCTION Throughout history, geology has shaped and changed the landscape of the San Francisco Bay Area. Natural forces such as plate tectonics, sediment movement, and water flow have formed the land into the mountains, valleys, creeks, and rivers we see today. Look at the area around your home or your school; what natural forces might have shaped the features we see today? In this activity you will get a chance to explore the geologic forces that have created not only the San Francisco Bay as we know it, but also a lot of the landscape we see surrounding the Bay Area, such as the Sierra Nevada mountains and the Central Valley. You will use everyday food items to represent various tectonic plates in order to learn about how the plates move and how this movement has created our local landscape. Finally you will get to eat your “plate tectonic models” and enjoy a tasty treat! MA TERIALS MATERIALS Your group will need • 4 slices of bread • 1 paper plate • 1 plastic knife • 1 plastic cup of peanut butter • 1 plastic cup of jelly • 1 plastic cup of snack mixture (optional) 74 Save The Bay’s San Francisco Bay Watershed Curriculum PROCEDURE 1. Spread peanut butter on two slices of bread and spread jelly on the other two slices. DO NOT PUT SLICES TOGETHER YET! 2. You may sprinkle some of the snack mixture on the slices if you have some. (optional) 3. When your teacher tells you to, put your slices together. Alternate the slices between peanut butter and jelly and put them together as you would a normal sandwich. 4. Discuss among your group: “What happens to rocks when they are exposed over time to pressure and heat?” How would expect your sandwich model of rock layers to change in appearance if subjected to heat and pressure? 5. Observe your teacher demonstrate the process of folding and faulting. 6. Then try it with your group. (Refer to your Fault Activity Demo Sheet.) Slowly bend the stack up toward the center; push in from the edges to mimic the process of folding. Folding and faulting created the Himalayan mountain range and many other ranges in the world. 7. Now cut the stack in half through the middle, forming 2 blocks and slide them to show strikeslip movements of the Earth’s crust. Demonstrate the strike-slip movement between two blocks by sliding the two sandwich blocks against each other and then horizontal to each other, following the diagrams on the Fault Activity Demo Sheet. The San Andreas Fault has this type of motion. 8. Cut one of your sandwich stack halves in half and show the vertical motion of the plates when pushed against each other. Use these sandwich blocks to demonstrate a normal fault by pushing the two blocks against each other and having one block slide downwards against the other (normal fault). Then have one slide upwards (reverse fault) against the other. The Owens Valley and Sierra Nevada fault zones area examples of normal faults. The Sierra Madre fault zone is an example of a reverse fault movement. 9. Then cut another of your stacks in thirds to show the formation of a valley, a graben fault movement. The graben fault is a special type of normal fault. The graben fault can be shown by cutting the remaining sandwich stack half into thirds and exerting force on the outer thirds to push the inner third downward. A fault-bounded ridge is called a horst, a fault-bounded valley is called a graben. 10. Take a core sample of one of your blocks by twisting a straw as you insert it into the densest part of the sandwich. After removing the straw, discuss the profile with your group, showing the pattern of materials (the alternating layers of peanut butter and jelly represent the different layers of rock). One of the basic rules of geology states that rock layers are laid down horizontally. Discuss with your partners which layers are the oldest and which the youngest in your model/core sample. Discuss your answers with your teacher and classmates. Save The Bay’s San Francisco Bay Watershed Curriculum 75 Peanut Butter and Jelly Geology A Study of Faults and Geologic Activity FAULT ACTIVITY DEMO SHEET 1. Slowly bend the stack up toward the center; push in from the edges to mimic folding. Folding and faulting created the Himalayan mountain range and many other ranges in the world. 3. Demonstrate a normal fault by cutting one of your sandwich stack halves in half and show the movement of a normal fault. Push the two blocks against each other and have one block slide downwards against the other(normal fault). Then have one slide upwards (reverse fault) against the other. ➜ ➜ ➜ ➜ ➜ ➜ 2. Cut the stack in half through the middle, forming 2 blocks and slide them together vertically, then horizontally to show strikeslip movements of the Earth’s crust. The San Andreas Fault has this type of motion. 4. Then cut another of your stacks in thirds to show the formation of a valley, a graben fault movement. Push the outer blocks towards the inner block, forcing the inner block downward. The Owens Valley is an expample of a Graben. ➜ ➜ ➜ ➜ ➜ ➜ ➜ ➜ ➜ ➜ 76 Save The Bay’s San Francisco Bay Watershed Curriculum