Over the Edge Activity 5.2: Map the Sea Floor
Name that feature
2D illustration
From the diagram below, match the numbered items to the correct feature listed below:
___
___
___
___
___
___
___
___
___
continental slope
continental shelf
continental rise
submarine trench
guyot
island
subduction
basalt
granite
3D imagery
Now, view this three-dimensional image of the Pacific Continental margin. Identify the features labeled
A-E. Use the USGS web site if you need help. http://www.usgs.org/
A is ____________________
B is ____________________
C is ____________________
D is ____________________
E is ____________________
Pacific Sea-Floor Mapping: Los Angeles Margin Open File Report: Perspective Views
http://geopubs.wr.usgs.gov/open-file/of02-162/persp.html
Identify these features. Write the letter after each.
___ continental slope
___ continental rise
___ continental shelf
___ submarine canyon
___ seamount
Contour maps
Another useful way to display depth information is using contour maps. Navigational charts are a good
example. The contour lines on the map (sometimes shaded) indicate regions of similar depth, called
isobaths. Print out the simulated chart of the southern California coast off Newport Beach, linked below.
Draw contour lines (i.e. isobaths) for each of the following depths (in fathoms): 5, 10, 25, 50, 100,
150, 200 and 250.
Discussion Questions
1. Compare the 2D illustration with the 3D image based on multibeam measurements. How do simple illustrations
oversimplify our “definitions” of sea floor features? In what ways do they help?
2. What prominent oceanographic feature appears off the coast of Newport Beach in the contour map? What are
the advantages of the contour chart for navigation of boats and ships?
3. Why does the 3D image provide the best understanding of sea floor features? How does this type of imagery
distort these features?
4. Why are visualization tools important for understanding the characteristics of the sea floor? How do multiple
tools give us a better picture of the sea floor than one tool alone?