Name______________________________________Per.____
Answer Sheet for Plate Tectonics Lab II
1. Find the East Pacific Rise on the maps above.
(a) What type of plate boundary is this? __________________________
(b) What type of igneous rock (formed from magma) is produced here?
_________________________
(c) Not that the topography is higher at this plate margin compared to the surrounding ocean basin?
What causes the topography here to be so much higher than the surrounding ocean basin?
2. Look at the west coast of South America on the maps above.
(a) What type of plate boundary is this? ______________________________
(b) What type of igneous rock (formed from magma) is produced here? ___________________
(c) What type of volcanoes are produced on the continent by this plate motion? (i.e. what is their
average composition and shape?)
(d) What makes these volcanoes so explosive?
3. Look at the maps above.
(a) How fast is the Juan de Fuca plate moving, and in what direction?
(b) How fast is the North American plate moving, and in what direction? (Estimate from the size of
the arrows on the map).
(c) What do you think will eventually happen to the Juan de Fuca plate? Why?
4. Go to http://earthquake.usgs.gov/research/data/slab/, and look at the maps of plate subduction. Use
the latitude scale and the map legends to estimate the degree at which the subducting slab is
descending.
Measure the size of a degree (or 5 degrees, depending on the scale) on your ipad with a piece of
scrap paper. Convert the degrees to kilometers to get your horizontal scale
1 degree latitude is = 111.3 km
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Use this scale to measure the horizontal distance across a subduction zone Be careful not to change
the scale (zoom in or out). Then calculate the degree at which the subducting slab is descending:
Degree of subduction = tan-1
vertical depth of slab
horizontal distance across slab
(a) Estimate the angles of subduction of these subduction zones using the equation above:
Cascadia:
Japan:
Santa Cruz/Vanuatu:
Scotia (Caribbean):
South America:
(b) Which plate is subducting at the steepest angle? What effect do you think steepness might have
on the depth of the trench? On the location of the volcanoes produced by subduction?
(c) Look at the map of the Alaska-Aleutian subduction zone. What is happening to the angle of
subduction of the Pacific Plate at this subduction zone?
(d) Measure the angle of subduction at the western egde of the zone (but where you can still see the
yellow colors showing a subduction depth of 100 km), and at the eastern edge of the zone. How
much change in the angle is there?
5. Hawaiian—Emperor Seamount Chain.
(a) Plot the data in Table 2.1 on the graph paper provided. (Use the whole sheet of paper and be sure
to label your axes.)
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(b) Use a ruler to draw a best-fit straight line through the data. What does the graph indicate about
the general relation between age and distance from Kilauea?
(c) Calculate the average rate of plate movement in centimeters per year (divide the distance by the
time interval over which the travel took place). Show your calculations. (1 km = 100,000 cm)
(d) The chain of seamounts bends where the Hawaiian and Emperor chains meet. When did the
change in direction in the chain occur? Explain how you arrived at your answer.
(e) Assuming the hotspot has remained stationary, what could have caused the chain to change
directions?
6. Look at the map of the Yellowstone hot spot above.
(a) Yellowstone produced calderas instead of tall volcanoes. What is a caldera?
(b) Why do you think Yellowstone might produce calderas instead of tall volcanoes?
(c) Calculate the approximate rate of motion of the North American Plate in cm/year. Use the
average age at the center of two of the extinct caldera locations and the following conversion:
1 mile = 160,000 cm
(d) How does this rate compare to the rate you used in Question 3b?
7. Go to http://geology.com/articles/east-africa-rift.shtml and answer the following questions about the
East African Rift .
(a) What is causing the “bulges” underneath the East African Rift Zone, and what are these bulges
doing to the land surface?
(b) What is a “triple junction” and how is it created? Name the three arms of the triple junction in
this area.
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(c) What type of lava is being erupted in large volumes in this area?
(d) Why is the crust “thinned” in this area?
(e) Why is this rift system considered complicated?
8. Look at the map of the San Andreas Fault and Answer the Following Questions:
(a) Transform Faults often connect segments of which other type of plate boundary?
(b) What are the names of the two plate boundaries that the San Andreas connect?
(c) Which direction is Los Angeles moving compared to San Francisco?_________________________
(d) What does this imply about the distance between those two cities millions of years from now?
9. Find the boundary between the North American Plate and the Eurasian Plate in eastern Russia on the plate tectonic
map, the seismicity map, and the map below. Many maps show this boundary tentatively, with a dashed line, or a broad
zone labeled “diffuse” or “uncertain” boundary.
(a)What geology do you observe along this phantom boundary?
Earthquakes:
Earthquakes:
None
Few
Shallow only
Active Volcanoes:
None
Ridges/Ranges/Mountains/Etc.:
Some
Deep only
Few
Many
Both shallow and deep
Some
Many
High elevations
Above surroundings
Modest
Nothing really
Trenches/Depressions/Etc. : Very low elevations
Below surroundings
Modest
Nothing really
Big Faults:
None
Few
Some
Many
(b) Compare this area with the types of plate boundaries from the earlier parts of today's lab. How does it resemble or
differ from them?
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