Essay/Short Answer Worksheet Key
 

1. Why do less dense plate ride over more dense plates in an oceanic-continental collision?
 
 When an oceanic-continental convergence occurs the denser oceanic plate will most commonly subduct beneath the less dense continental plate creating a trench.  Once the subducting oceanic crust reaches a depth of about 100 kilometers, melting of the crust and the overlying mantle begins forming a magma.
 
2. What are some other ways you can think of to measure the sea floor?

Answers may vary.
 
 
3. What are five uses for satellite altimeter data?  Can you think of other ways this technology can be used?
 
 Students will have to use additional sources to answer this question.
 
 
4. How are high resolution images made?
 
 As the spacecraft orbits the earth it collects a continuous profile of geoid height across an ocean basin. Profiles from many satellites, collected over many years, are combined to make high resolution images.
 
5. Why are gravity maps the best maps to use for reconnaissance of the sea floor?
 
 The satellite-derived gravity grids reveal all of the major structures of the ocean floor  having widths greater than 10-15 km (6-9 mi). This resolution matches the total swath width of the much higher multibeam mapping system on a ship (100 m resolution) so the gravity maps are the perfect reconnaissance tool for planning the more detailed shipboard surveys. Scientists aboard research vessels use the gravity grids along with other measurements to optimize their survey strategy; in many cases this is done in real time. The cost to operate a research vessel is typically $20,000 per day so these gravity data have become an essential item.