| Share
 

ocean

Continental Shelves, Slopes, and Rises

Virtually all continents are surrounded by a gently sloping submerged plain called the continental shelf, which is an underwater extension of the coastal plain. The continental shelves are the regions of the oceans best known and the most exploited commercially. It is this region where virtually all of the petroleum, commercial sand and gravel deposits, and fishery resources are found. It is also the locus of waste dumping. Changes in sea level have alternatingly exposed and inundated portions of the continental shelf. Continental shelves vary in width from almost zero up to the 1,500-km-wide (930-mi) Siberian shelf in the Arctic Ocean. They average 78 km (48 mi) in width. The edge of the shelf occurs at a depth that ranges from 20 to 550 m (66 to 1,800 ft), averaging 130 m (430 ft). The shelves consist of vast deposits of sands, muds, and gravels, overlying crystalline rocks or vast thicknesses of consolidated sedimentary rocks. Although there is a great variation in shelf features, nonglaciated shelves are usually exceptionally flat, with seaward slopes averaging on the order of 205 m per km (10 ft per mi), or less than 1° of slope. The edge of the shelf, called the shelf break, is marked by an abrupt increase in slope to an average of about 4°.

The continental slopes begin at the shelf break and plunge downward to the great depths of the ocean basin proper. Deep submarine canyons, some comparable in size to the Grand Canyon of the Colorado River, are sometimes found cutting across the shelf and slope, often extending from the mouths of terrestrial rivers. The Congo, Amazon, Ganges, and Hudson rivers all have submarine canyon extensions. It is assumed that submarine canyons on the continental shelf were initially carved during periods of lower sea level in the course of the ice ages. Their continental slope extensions were carved and more recently modified by turbidity currents—subsea "landslides" of a dense slurry of water and sediment.

Many continental slopes end in gently sloping, smooth-surfaced features called continental rises. The continental rises usually have an inclination of less than 1/2°. They have been found to consist of thick deposits of sediment, presumably deposited as a result of slumping and turbidity currents carrying sediment off the shelf and slope. The continental shelf, slope, and rise together are called the continental margin.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

More on ocean Continental Shelves Slopes and Rises from Infoplease:

  • ocean: Continental Shelves, Slopes, and Rises - Continental Shelves, Slopes, and Rises Virtually all continents are surrounded by a gently sloping ...
  • ocean - ocean ocean, interconnected mass of saltwater covering 70.78% of the surface of the earth, often ...

See more Encyclopedia articles on: Geology and Oceanography


Premium Partner Content
HighBeam Research
Documents Images and Maps Reference
(from Newspapers, Magazines, Journals, Newswires, Transcripts and Books)

Research our extensive archive of more than 80 million articles from 6,500 publications.

Additional search results provided by HighBeam Research, LLC. © Copyright 2005. All rights reserved.

24 X 7

Private Tutor

Click Here for Details
24 x 7 Tutor Availability
Unlimited Online Tutoring
1-on-1 Tutoring