The Continental Margin

Objectives:

1. Identify the methods scientists use to map the ocean floor.

2. Describe the techniques of echo sounding and core sampling.

3. Describe the parts of the continental margin.

4. Compare and contrast active and passive continental margins.

Key Terms:

echo sounding core sampling continental shelf continental slope continental rise active continental margin passive continental margin submarine canyon turbidity current

Notes:

The continental margin is the underwater part of the continental crust that extends out into the ocean. Whether it is considered active or passive depends on its proximity to active plate boundaries. The major parts of the continental margin include:

Continental shelf - extends from the shore to the continental slope

	narrower in active and wider in passive margins
	relatively level compared to the slope

Continental slope - water depth increases quickly as you move away from the shelf

Continental rise - connects the slope to the Abyssal plain (ocean floor) in passive margins

Deep Sea Trench - border of the subduction zone that separates the slope (continental plate) from the diving Abyssal plain (oceanic plate)

Submarine Canyons - formed from underwater mudslides and earthquakes

	many are larger than the grandcanyon
	can extend from the shelf to the Abyssal plain

(www.soc.soton.ac.uk/CHD/EUROSTRATAFORM/ IMAGES/DOW1.gif))

(tlacaelel.igeofcu.unam.mx/~GeoD/ colision/figs/andian.jpg)

Studying the Ocean Floor

With the advent of increasing technology, the study of the ocean floor has increased dramatically with the advent of satellites, deep water submersibles, and echo technology.

Echo Sounding (Sonar)

	A sound impulse travels to the bottom of the ocean and bounces back where it is read at the boat
	The depth is interpreted using the speed of sound in water
	Since the sound traveled down and back, the distance is 1/2 the time multiplied by the speed of sound in ocean water

Single-Beam Bathymetry (www.divediscover.whoi.edu/images/ sonar_swath_top.gif)

Sediment Sampling

Since the ocean floor is layered with sediments, long cylindrical samples are removed from the sea floor to study rocks at different depths.

provides a geological history of the region

Satellites

Map the ocean floor by the differences in the height of the ocean water

	water is higher over a sea mount
	water is lower over a trench
	gives a wider view of the ocean than was possible with Sonar alone

(www.ngdc.noaa.gov/mgg/ image/figure01.gif)

Last modified: February 03, 2004