Geology 113
Physical Characteristics
of the Ocean Floor

Print this webpage so you have a hard copy of the assignment. Bring the hard copy to lab.

Objectives:

Completing this lab should help you develop the following concepts related to the physical features of the ocean floor:
  1. The ocean floor is not a flat, featureless surface.
  2. Plate tectonic theory is useful in understanding many features of the ocean floor.
  3. The Atlantic and Pacific Ocean floors are very different in terms of size and features.
  4. The features one would encounter crossing the Atlantic Ocean floor.
  5. Technology and science are fundamentally intertwined in our efforts to understand the world's oceans.

Key Terms:

continental shelf
continental slope
continental rise 		submarine canyon
submarine fan
mid-ocean ridge 		ocean trench
guyot
seamounts 		abyssal plain
oceanic islands

Materials:

The Floor of the Oceans (B.C. Heezen and M. Tharp) Investigations into Physical Geology (J. Mazzullo)

Part One: Pacific Ocean

Refer to the map: The Floor of the Oceans to answer the following questions.
  1. Describe any differences you observe between the eastern Pacific Ocean floor and the western Pacific Ocean floor.

  2. What major physical feature does the southern Pacific Ocean floor contain that the northern Pacific Ocean floor appears to lack? (region north of 200 N).

  3. Look at the region in the Pacific Ocean between 1000 --1400 W and 00 -- 400 N. What are the "bumps" you see on the ocean floor called? How do they form? According to one estimate, the Pacific Ocean has 20,000 such features.

  4. Use plate tectonic theory to explain the relationship between the following two features of the Pacific Ocean floor (note that the trends are perpendicular to one another):
    The SW-NE trending feature in the southeastern Pacific
    The NW-SE trending features of the western Pacific.

  5. Use plate tectonic theory and your understanding of the nature of continental margins (active versus passive) to explain the difference between the width of the continental shelf on the east side of southern South America and the west side of southern South America.

Part Two: Atlantic Ocean

Refer to the map: Bathymetry of the northern Atlantic Ocean on page 215 of your lab manual (Investigations into Physical Geology) to complete the following.
  1. Draw a line between Charleston, South Carolina and Dakar, Africa. Suppose AT&T wants to lay a fiber-optic cable across the ocean floor to connect their communications networks in these two cities. Staring with the shore of Charleston, write a story that describes the major features on the ocean floor that the cable would traverse. Refer to the set of terms above. Point out the width and sizes of the features.

Part Three: Technology in oceanography

You must use the World Wide Web to compete this portion of the assignment. Complete this individually so that you learn how to use the World Wide Web.

World Topography

Click on the Open button and type in the following URL: http://rainbow.ldgo.columbia.edu/datacatalog.html Click on the link World Topography. You will see a colored map called WORLDBATH topography. Note the key below the map. Numbers and colors above zero refer to elevation. All features above sea level have elevation. Numbers and colors below zero (i.e., negative topography) refer to bathymetry. Bathymetery means depth below sea level. Answer the following questions.
  1. What color is used to identify areas of the ocean floor that are deeper than 4500 meters?
  2. Which ocean, the Atlantic or Pacific, has the greatest area of ocean floor that is deeper than 4500 meters?
  3. How deep is the crest of mid-ocean ridge?
  4. The continental shelf extends from a depth of 0 meters at the edge of a continent to a depth of about 200 meters at the shelf edge. Compare the widths of the continental shelf on western and eastern sides of North America. Do the same for South America. Which sides of these continents are passive margins? Which sides are activie margins? Explain your answer.
  5. Print out the page and attach it to your lab.

Ridge Multibeam Synthesis Project - Lamont-Doherty Earth Observatory

Click on the Open button and type in the following URL: http://imager.ldeo.columbia.edu/ridgembs/ne_pac/html/home.html At this site, you will see a map of the world with red dots. Click on the red dot in the Atlantic Ocean between New York and Spain. This will bring up a page titled "North Mid Atlantic Ridge." Click on the box called Gridded Data. This will zoom in on the area. Click on box number 10 to zoom in. The next page youšll see will be called Area 10 grid. Note the colors for bathymetery. Click on the map - this will zoom in on the map. Once you have the map loaded onto the screen, use the scroll bars on your screen to examine different portions of the map. Under File at the top of your screen, open up the "page setup" box. Once the box is open, do the following: Reduce the page size to 60%. Change the page orientation to horizontal. Under "header," put the location in the left header and title in the right header. Then click "OK" Print the map and attach it to your lab.

The URL of the map you are printing is

http://imager.ldeo.columbia.edu/ridgembs/n_mar/imagery/imag_gifnma210u.gif
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