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 movement? Station 3 f. 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? i. Would you expect to find a thicker accumulation of sediment at spreading centers or subduction zones? Why? j. 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? l. 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: Canyon 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.