Submarine Canyons Along the Edges of continental Shelves
Marine Canyons and Valleys
Submarine canyons often have tributary systems similar to those of rivers on land opening their way through valleys. Submarine canyons seem to slope away from their courses and lack basin depressions. Very large submarine canyons are difficult to be related to rivers excavated by currents on land. The ones that appear to have been carved by rivers and erosion probably required very powerful forming means.
Submarine canyons are steep-sided marine valleys that extend along the continental shelf and into continental slopes. Rivers and continental faults often flow into submarine canyons. A continental shelf is the region of a continent that expands from under the seashore and into the deep-ocean floor. The limit of a continent is not the coastline, but the edge of the continental shelf, which lies under water. The average width of a continental shelf is of approximately 65 km (40 miles). Marine canyons and valleys are often found along the edges of continental shelves.
A continental shelf often starts at the boundary of the coast line to a point called the shelf break. From the shelf break, the continental floor gets deeper and steeper into what is known as the continental slope. In the majority of coastal regions, continental shelves expand for less than 1 km (0.62 miles), such as the coast of California, while in other regions, they may extend for over 1,000 km (620 miles), such as in the case of the northern coast of Siberia. The average depth of a continental shelf is of about 65 meters (213 feet), permitting the penetration of sunlight, and the perfect conditions for marine life to prosper.
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Just as in continental land, land features, such as mountains, valleys and canyons can be found. A submarine canyon is often found as a crack on the sea floor and into the continental slope, sometimes extending further into the deep ocean floor. Some marine canyons may extend as submarine channels (abyssal channels) for several hundreds of kilometers. While sunlight maybe abundant over the continental shelf, little of it penetrates on marine canyons.
Often, submarine canyons are found as extensions of continental rivers and faults. Such is the case of the Carmel Canyon, which lies on the Monterey Bay and coincides with the San Gregorio fault.
Formation of submarine Canyons
There are a number of theories about the formation of submarine canyons. One early theory states that, submarine canyons may have been formed during the glacial period, when sea water level decreased 125 meters (410 feet) and rivers could have flowed to the very edges of the continental shelf. This theory was discarded because erosion could not have reached ocean depths of 3000 (9840 feet) meters, which is where marine canyons are most often found.
The main process of marine canyon erosion to date is thought to be turbidity currents and submarine landslides. Turbidity currents move down the continental slope, carrying sediments which have been deposited up the slope. They usually move faster than the water through which they move due to a higher density content. They are thought to be caused by earthquakes, sediment deposited by rivers and slumping.
Formation of a Canyon
Besides turbidity currents, it is believed that the action of landslides affects the development of a canyon. Landslides originate when the stability of a slope weakens. Such a change can be caused by an earthquake, volcanic eruption, glacier melting and other factors.
In the present, Scientists know that many factors, in different periods in history, may have contributed to the formation of submarine canyons in a lesser or greater degree. The physical structure of marine canyons requires that various dynamic building factors occur to produce transportation of sediment and erosion at the upper layers. Turbidity currents of various types, storms, landslides, earthquakes, tidal fluctuations, ice melting are some of the factors considered for the formation of submarine canyons.
Due that submarine canyons are found in shallow, as well as deep ocean waters, they are inhabited by a great diversity of marine life. Generally, landslides from the walls of canyons deposite very rich-nutrient sediments over the ocean floor, from which deep ocean organisms feed. Most biodiversity found in the bottoms of marine canyons are not unique to their environment, as they´re also found in other ocean ecosystems. The cracks along the walls of submarine canyons are inhabited by invertebrates, including corals and tunicates, sea stars, clams, worms, and small fish.
Monterey Canyon starts at the small coastal city of Moss Landing, California and from there; it extends 153 km (95 miles) into the Pacific Ocean, reaching ocean depths of over 3,600 meters (11,800 feet). With one mile deep, it is comparable in depth to the Grand Canyon in Arizona; however, from the ocean´s surface to the Canyon´s bottom, it reaches two miles of deepness. The Monterey Canyon forms part of a system of other Canyons, including Carmel and Soquel Canyons. This canyon is very rich in marine biodiversity.
Monterey Canyon, off the coast of California
Amazon Canyon, expanding from the Amazon River
Hudson Canyon, extending from the Hudson River
Bering Canyon, in the Bering Sea
Indus Canyon, from the Indus River
Ganges Canyon, from the Ganges River
Baltimore and Wilmington Canyons, in the coast of Maryland and Delaware
Whittard Canyon, off the southwest coats of Ireland
Zhemchug Canyon, largest canyon in the world, in the Bering Sea
Congo Canyon, largest river canyon (800 km or 497 miles), expanding from the Congo River
Aviles Canyon, deepest (over 4,750 meters 15584 feet from the slope) in the world at the southern Bay of Biscay, Spain
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