Homework1-Part E
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Stanford University *
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Geography
Date
Feb 20, 2024
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Part E: Investigating Plate Tectonics through Google Earth (38 pts) Your task:
In this investigation you will examine data sets of topography, bathymetry (ocean depth), volcano location, earthquake location, and ocean floor age to determine the location and attributes of different plate tectonic boundaries. After looking at global plate tectonics, you will look at our study regions more closely. Tips
Please refer to “google earth tip sheet” for basic features and functions of google earth
When you bring files into Google Earth, make sure you save them to My Places and then File
Save
Save My Places. That way if Google Earth crashes, everything will reload automatically when you restart.
You should uncheck data sets that you are not using for a given question because they may interfere with each other (particularly the Age-of-Ocean-Floor).
Earthquakes and volcanoes will not show up until you are somewhat zoomed in. You will probably find that an eye altitude of 4000-5000km is best for balancing view scope with data visibility. a. Atlantic Ocean Double-click plate tectonics exercise part 1.kmz to open it in Google Earth (don’t load plate tectonics exercise part2.kmz yet or leave it not visible) Make the Atlantic cross-section visible (located in the Cross-sections folder) and Show the Elevation Profile (by first selecting or highlighting the Atlantic cross-section under “Places” panel on the left, and then right clicking it and choosing “Show the Elevation Profile”… on Mac you will need to “control-click” instead of right click). 1.
On the cross-section, mark the transitions from continental crust to oceanic crust (Use what you know about plate thickness. The actual sea level line does not necessarily tell you where the edge of the continental crust is.)
2.
Mark the plate boundary between North American and African plates.
3.
Using earthquake, bathymetry, and ocean floor age data, describe the lines of evidence that support the location you have chosen for the plate boundary. Both sides on the location have the same elevation, and it increases as it moves toward the center, which is a sign of a mid-oceanic ridge that forms at a divergent plate boundary. The location marked has a lot of shallow earthquakes, indicating the presence of a divergent plate boundary. Newer rocks also appear at the center, which means that new crust is forming here. This also points to the presence of a divergent plate boundary. 4.
What type of earthquake (shallow or deep) occurs along the plate boundary? Shallow earthquakes occur along the plate boundary because the plates are moving apart. 5.
Why does the plate boundary have an elevated profile (i.e. why the mid ocean ridge?) (
Consider density and temperature) At a divergent plate boundary, the partially molten and less dense asthenosphere rises to fill the gap, which creates a buoyant force that causes the elevation of the mid-ocean ridge. 6.
What rate (in mm/yr ) are each of the plates moving relative to the boundary? (You will need to use the ocean floor age data and the Ruler tool to determine this) The oldest age from the ocean floor age data is 150 million years. The length of the ocean floor from the mid-oceanic ridge to the continental rise is about 3050 kilometers. Rate of plate movement = (3050 * 10^6) / (150 * 10^6) = 20.34 (mm/yr). 7.
What type of plate boundary is illustrated here? Divergent (constructive) plate boundary. 8.
Name three other places in the oceans where you observe the same types of boundary: East Pacific Rise, East African Rift, and Juan de Fuca Ridge b. Sumatra Make the Sumatra cross-section visible and Show the Elevation Profile.
9.
Mark the boundary between the Indo-Australian and Eurasian plates at the Earth’s surface. Mark the location of volcanoes.
The X is the boundary, the arrows point to volcanoes 10.
Using earthquake, bathymetry, and ocean floor age data, describe the lines of evidence that support the location you have chosen for the plate boundary. The subduction of the Indo-Australian plate under the Eurasian plate causes sediment to crumple and initiates the mountain building process, leading to the decrease in bathymetry, which marks the plate boundary. 11.
On the cross-section, mark in the approximate location of the earthquakes (horizontally and vertically). What are these earthquake locations demarcating? Most of the earthquakes in the data provided occurred quite deep (20~50 km) so I can’t demonstrate that is in the diagram, but I have marked the general locations. The earthquake locations demarcate the overriding plate from the subducting plate. 12.
What is the rate of Indo-Australian Plate motion? (this can be found directly from the Plate Convergence data)
70 mm/year. 13.
What type of plate boundary is it? It is a convergent plate boundary. 14.
Where else on the globe do you observe the same types of boundaries? Andes Mountains, Japan Trench, Mariana Trench.
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c. California Zoom in on California (there is no cross-section, just make sure that the Continental Transform Fault path is visible).
15.
The transform fault that is shown here is the famous San Andreas Fault that separates the Pacific Plate from North American Plate in this area. What type of earthquakes (shallow or deep) are associated with transform faults? Shallow earthquakes are associated with transform faults. d. Pacific Northwest Make the Juan de Fuca cross-section visible and Show the Elevation Profile.
16.
Based on what you determined in the first two sections, what type of plate boundaries do you see represented here? Mark where you think they are on the cross-section. What is your evidence for each? The boundary on the left is a divergent boundary, while the one on the right is a convergent boundary. The divergent boundary is characterized by a prominent mid-oceanic ridge and exhibits a similar elevation profile as the mid-Atlantic ridge examined. The convergent boundary exhibits trench formation and volcanic activity. 17.
If the first two sections showed more “typical” plate boundaries, what characteristics of this area seem unusual? Unlike more typical plate boundaries as we have examined, this area has the interaction of multiple boundaries with three participating sections. 18.
The convergence rate between Juan de Fuca Plate and North America? (make sure Plate Convergence path is visible) How quickly is new Juan de Fuca Plate crust being generated? (same way you did in #6) Do you think the plate is getting bigger, smaller, staying the same, or cannot be determined? 39 mm/year. Rate of plate movement = (400 * 10^6) / (10 * 10^6) = 40 (mm/yr). It is getting bigger as newer crust is being formed.
19.
Now watch the Pacific_spreading.mov animation that came in your zipped file. How would you answer #18 now? It is getting smaller as time goes on and should soon subduct underneath the North American plate. e. Himalaya Make the Himalaya cross-section visible and Show the Elevation Profile.
20.
You know from the reading that this is a continent-continent convergent margin. Using topography, mark on the cross-section where you think the plate boundary is. 21.
Watch the animation IndiaAsiaCollision_EMVC2008.mov. Do you still agree with where you located the plate boundary? Yes. 22.
What has been the evolution of this plate boundary over the last 60 million years? Collision between India and Asia happened 55-50 million years ago. From 50-40 million years ago, the collision led to the uplift of the Tibetan plateau. 40-20 million years ago, intense convergence formed the Himalayas. And from 20 million years until now, the ongoing convergence sustains uplift and seismic activity in the Himalayan region. 23.
Given that you know the major driving force behind plate tectonics is the downward pull of descending plates, how do you explain that India is still colliding with Asia at over 40mm/yr? What is keeping it going? (it may help to zoom out and consider the large tectonic plate that India is part of. Make part2.kmz visible to see plate boundaries.)
The buoyant nature of continental lithosphere sustains the collision between the India and Asia. The Indian plate resists subduction into the mantle, leading to the formation of the Himalayas. This ongoing convergence and resistance to subduction contribute to the sustained collision. 24.
What depth of earthquakes are associated with the Himalayan-Tibetan region? Typically in the range of 5-20 km.
f. Earthquakes in our study region Make sure the part2.kmz file is visible. 25.
Using the Earthquake data (which includes Mag 6 since 2000 and about half a year of smaller quakes), which type of plate boundaries are associated with bigger earthquakes and more numerous earthquakes? Bigger and more numerous earthquakes are associated with convergent plate boundaries. 26.
Would you pick out either of our two case regions (Pacific Northwest and Himalaya) as being particularly seismically active based on the last decade of earthquakes? Based on the last decade of earthquake data, I would characterize both regions as seismically active.
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