Submarine canyon
From Freepedia
A Submarine canyon is a steep-sided valley on the seafloor of the continental slope. Submarine canyons are generally found as extensions to large rivers, and have been found to extend 1km below sea level, and extend for hundreds of kilometers.
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Characteristics
Submarine canyons are more common on steep slopes than on gentle slopes. They show erosion through all substrates, from unlithified sediment to crystalline rock. They are more densely spaced on steep slopes while being rare on gentle slopes. The walls are generally very steep or vertical. The walls are subject to erosion by turbidity currents, bioerosion, or slumping.
Examples of submarine canyons
- Congo canyon, the largest river canyon, extending from the Congo river, is 800 km (500 miles) long, and 1,200m (4000 ft) deep.
- Amazon canyon, extending from the Amazon river
- Hudson canyon[1], extending from the Hudson river
- Ganges canyon, extending from the Ganges river
- Indus canyon, extending from the Indus river
- Monterey bay canyon, off the coast of central California
- La Jolla and Scripps canyon, off the coast of southern California
- Bering canyon, in the Bering sea
Formation of submarine canyons
Two mechanisms have been suggested for the formation of submarine canyons, which may have worked in concert:
- Canyons may have been carved during a time when sea level was lower than present and rivers were able to flow out to the edge of the shelf. This theory is supported by the fact that many (but not all) canyons are found offshore from major rivers. A difficulty with this theory is that the sea level would have had to have been 3000m lower to account for the canyons.
- Canyons may have been carved by turbidity currents (dense, sediment-laden currents which flow down the continental margin, triggered e.g. by an earthquake).
