Lab handout B for Lab#2: Marine Geology

Lab handout B for Lab#2: Marine Geology
As you visit stations 1-7 around the lab room, work together to answer the questions in the lab
manual and on this sheet. Note stations 1 and 7 of Exercise 2 in your lab manual will not be
covered in this lab and Station 4 is optional. We will go over the major points during the last 5
minutes of class. These questions will not be graded---they are for you to study from.
Station 1--Contour maps (not Lab manual station 1)
a. What is the datum?
b. Do contour lines that are closer together represent a steeper or shallower slope?
Station 2
c. Figure 2-B tells you that a range of earthquake depths, from shallow to deep, is characteristic
of subduction zones. Use this information and figure 2-A to determine at least 2 locations
where subduction is occurring.
d. Note the occurrence of earthquakes between India and China--in fact a 6.5 earthquake
occurred in China early this year. What do you think is happening in this region? (Hint:
What geologic feature is found here?)
e. In the text you read about hot spots--now look at the Hawaiian Islands and Emperor
Seamounts. What can island chains formed by a hot spot tell you about the direction of plate
Station 3
Find the East Pacific Rise and the Mid Atlantic Ridge (both spreading ridges) on the map of
bedrock geology. Comparing the patterns on the seafloor around these ridges, what can you
say about their relative spreading rates?
g. Look at the plate boundaries map on p. 9 of your lab book. Is plate movement causing the
Atlantic Ocean to become smaller or larger?
Pacific Ocean?
Station 4-----Optional
Station 5
h. Why does oceanic crust tend to "sink" as it moves away from the spreading centers?
Would you expect to find a thicker accumulation of sediment at spreading centers or
subduction zones? Why?
Does crystal grain size increase or decrease as you go deeper into the lithosphere at a
spreading ridge? Why?
Station 6
k. Why do most metamorphic rocks form at subduction zones, but not at spreading centers?
Why do explosive volcanoes occur near subduction zones?
m. What role does the relative density play at subduction zones?
Station 7--Geology off the Washington Coast. (not station 7 from the lab manual)
n. Look for the following features on the physiographic map of the Pacific NW coast:
Spreading ridge
Continental slope
Abyssal plain
continental shelf
transform fault
continental rise
o. Subduction is occurring of the coast----Speculate as to why there is no trench visible.