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Geology 2 – Physical Geology Lab Lab #2 – Interpreting Tectonic and Bathymetric Maps Student Outcomes: Be able to understand and use basic map information, including scale, contour interval, legend, etc. Be able to recognize tectonic features, including mid-oceanic ridges, seamounts, trenches, and plate boundaries on a bathymetric map Be able to identify the three types of tectonic plate boundaries using a bathymetric map Understand the processes occurring at the three types of plate boundaries Be able to determine the direction of tectonic plate motion by interpreting seafloor features on a bathymetric map Create a cross-section using a bathymetric map Understand and use contour lines and contour intervals on a map Recognize and identify topographic features associated with the San Andreas and San Gregorio Faults Be able to identify seafloor features such as continental shelf, continental slope, continental rise, submarine canyons, and seamounts on a bathymetric map. Develop a beginning understanding of how our world works so the student can make more accurate assessments of presented information about our world and become responsible leaders and voters. Materials: Map of “Measured and Estimated Seafloor Topography” from World Data Center (Note: This map is on reserve at the MPC library and at the class website) Map of “Monterey Bay National Marine Sanctuary” from Monterey Bay Sanctuary Foundation, 1999. Wall map of the World Various other bathymetric maps and resources available during lab Plate tectonic map of the world Globe Bathymetry Map Orientation 1) Using the bathymetric map “Measured and Estimated Seafloor Topography,” locate the colored depth scale at the top. What color represents the deepest areas of the ocean? Lightest purple 2) What depth is represented by green? (Hint: Interpolate to the nearest 500 meters) 3500 m 3) What is the average depth of the oceans abyssal plains? 5500 to 6000 m 4) How would you distinguish ocean floor that is 6,000 meters deep from ocean floor that is 7,000 meters deep? 6000 m deep is dark purple; 7000 m deep is light purple Atlantic Ocean 1) Using the world wall map or other lab resources, name at least one place where the Mid-Atlantic Ridge is exposed above sea level. Iceland; Azores 1 Geo 2 – Physical Geology Lab Interpreting Tectonic and Bathymetric Maps 2) Using the bathymetric map “Measured and Estimated Seafloor Topography” locate the deep, broad abyssal plains of the Atlantic Ocean. Where are there deeper areas of the Atlantic Ocean? (Hint: Remember the deepest bathymetry is shown by a light purple color, not deep purple or blue.) Name or indicate the latitude (using the scale on the right and left margins of the map) at least one of two clearly visible locations. What is the tectonic setting of these deepest areas? Deep-sea trenches where subduction of oceanic crust occurs. Scotia Trench near 60º S is 6000 to 7000 m deep; Caribbean Trench is another location. 3) Is the east coast of South America at a plate boundary or in the middle of a plate? How do you know? It is in the middle of the plate because there is not mid-ocean ridge or trench, nor any evidence of rifting or transform faulting along the east coast of South America. 4) How does the shape of the Mid-Atlantic Ridge compare to the shape of the continental margins on either side of the Atlantic Ocean? Why do you think this shape relationship exists? The shape of the continental margins on either side of the Atlantic Ocean mimics the shape of the MidAtlantic Ridge. The shape of the ridge is preserved along the continental margins reflecting the original splitting apart of the land mass at the Mid-Atlantic Ridge. Africa and South America continue to move away from each other as sea floor spreading continues along the Mid-Atlantic Ridge. Indian Ocean 1) Is Madagascar part of the African Plate? Why or why not? Yes. Only shallow water separates Madagascar from the African continent, and there is no evidence of a plate boundary (i.e., trench, mid-ocean ridge, transform features) between them. 2) Is Madagascar part of the African continent? Why? Or why not? No. Deep water separates Madagascar from the African continent.. 3) India and Australia are both part of the Indian Plate. Examining the portion of this plate northwest of Australia, what features are found along the northeast boundary of the Indian Plate? What kind of tectonic boundary is this? Trench – a convergent boundary and a subduction zone where the Indian Plate is subducting under the Eurasia Plate. 4) What features are found along the southwest boundary of the Indian Plate? What kind of tectonic boundary is this? Mid-oceanic ridge is a divergent plate boundary. 5) Considering your observations in answering the previous two questions, what direction do you think the Indian plate moving? Explain your conclusion. Indian Plate is moving northeast – oceanic crust forms at mid-ocean ridge along SW boundary and is subducted in the trench located in the northeastern margin of the plate. Pacific Ocean 1) What features do you find along the western boundaries of the Pacific Plate? What type of tectonic boundary is this? Deep-sea trenches along a subduction zone, a type of convergent plate boundary. 2) What features do you find along the southeastern boundary of the Pacific Plate? What type of tectonic boundary is this? Mid-ocean ridge, which is a divergent plate boundary. 2 Geo 2 – Physical Geology Lab Interpreting Tectonic and Bathymetric Maps 3) Considering your observations in answering the previous two questions, what direction do you think the Pacific Plate is moving? The Pacific Plate is moving northwest as new oceanic crust is formed by the mid-ocean ridge in the SE and crust is subducted in the trenches along the western boundaries of the plate. 4) Locate the Hawaiian-Emperor Seamount Chain. Notice the bend in the chain. How might this bend have formed? The age of the rocks at the bend is 43 million years old. Why do you think the seamounts become progressively deeper to the north and west of Hawaii? A change in the direction of the Pacific Plate movement. Seamounts become denser as they cool, causing them to subside. The older seamounts are progressively deeper the farther away from the source hotspot. 5) Where in the Pacific Ocean would you expect to find the oldest oceanic crust? Why? At a subduction zone farthest away from the mid-ocean ridge where the new crust is being formed. 6) Locate the Marshall Islands and the Louisville Ridge in the southwest Pacific on the map at the end of the lab worksheet. Notice how the islands and the ridge seem to connect with one another. What do you think happened to the missing islands in between? What feature do you see on the bathymetric map that supports your guess? The missing islands were subducted. The trench along here supports this idea. 7) Notice the chain of islands extending north from New Zealand. Why might you expect to find active volcanoes on these islands? What kind of volcanoes would you expect them to be? Explain using what you know about plate boundaries. Active volcanism is characteristic of subduction zones and deep-sea trenches. Volcanoes would be explosive -- strato-volcanoes with steep sides. 8) Using the bathymetric map, find the mid-ocean ridge in the southern Pacific Ocean at about 60 degrees south. Notice how the mid-ocean ridge is composed of many offset sections. What type of plate motion occurs in the linear areas between the offset ridges that are perpendicular to the ridges? (Hint: Consider the plate motion that you know occurs at the mid-ocean ridges.) Transform or left lateral strike-slip motion Cross-sections Using the bathymetric and topographic maps in lab, draw cross-sections along the lines indicated on the map at the end of the worksheet. Use the lines A-B, C-D, and E-F provided on the next page to draw your crosssections. (Note that cross-section C-D goes right through Hawaii.) In your cross-sections, be sure to include and label the following features, if present: Lithosphere Hot spots Asthenosphere Trenches Crust Convergent margins Approximate topography and bathymetry Divergent margins Sea level Transform margins Sites of active volcanism Mid-ocean ridges 3 4 Monterey Bay Area Refer to the map of the Monterey Bay National Marine Sanctuary put out by the Monterey Bay Sanctuary Foundation (1999) to answer the questions in this section. 1) Find the San Andreas Fault (SAF) on the map. a. In the northernmost part of the map, which bay marks the course of the SAF? Tamales Bay and Bolinas Lagoon b. Near what famous landmark is the SAF located offshore rather than onshore? Golden Gate Bridge c. Near what highway does the SAF cross the Pajaro River near Watsonville? Hwy 101 or the unlabeled Hwy 129 from Watsonville d. In the southern portion of the map, which highway follows the SAF most closely? Hwy 25 e. What two topographic features can one recognize that identify the location of the SAF on this map? Long linear valleys and linear ridges f. What kind of fault is the San Andreas Fault? Transform or right-lateral strike-slip 2) Note the light blue lines labeled with numbers in the offshore portion of the map. These lines are called contour lines. A contour line is a line joining points of equal elevation, or, in this case, of equal depth. The contour interval is the vertical distance between contour lines. a. Referring to the map legend, in what unit is the depth recorded on this map? meters b. What is the contour interval on this map close to shore? 20 m c. What is the contour interval on this map far from shore? 200 m 3) The Monterey Bay National Marine Sanctuary map shows several seafloor features exceptionally well, including examples of the continental shelf, continental slope, continental rise, submarine canyons, and seamounts. Locate and observe examples of each of these features on the map in lab. 4) Find the Monterey Fan in the southwestern region of the map. What type of material would you expect to find here? How would it have gotten there? What could be the source? We would expect fine-grained material (clay and silt particles) to have been transported through the Monterey submarine Canyon and deposited on the Monterey Fan. The source is erosion from the land and transported by rivers to the mouth of the Monterey Canyon. 5) How deep is the Monterey Canyon near the intersection with the Carmel Canyon in meters and in feet? (One meter = 3.28 feet) 2000 m = 6560 feet 6) Find the reference map that shows the trace of the San Gregorio Fault south of San Francisco to the Santa Lucia Range. Trace the San Gregorio Fault on the map in you lab handout. Using the Marine Sanctuary map, describe two topographic features that are associated with the trace of the San Gregorio Fault. The linear ridge north of Half Moon Bay and the Carmel Canyon off-shore Congratulations on completing the Interpreting Tectonic and Bathymetric Map Lab! Remember the bathymetric and the Marine Sanctuary maps are available for your use at the reserve desk at the library. The bathymetric map is also available on the class website. 5 Geo 2 – Physical Geology Lab Interpreting Tectonic and Bathymetric Maps Figures for Lab Worksheet Pacific Ocean – questions 6 and 7 Cross-Sections Map MPC/Geo2/Labs/Lab #2 - Interpreting Tectonic and Bathymetric Maps.doc/LTS 6