Deep ocean trenches
Deep ocean trenchesDeep Ocean Trench
A trench is any long, narrow, steep-sided depression in the ocean bottom. The deepest known depression of this kind is
the Mariana Trench, which lies east of the Mariana Islands in the western North Pacific Ocean . Of the Earth's 20 major trenches, 17 are found in the Pacific. The only Atlantic trenches are the Puerto Rico Trench north of the Caribbean islands and the South Sandwich Trench east of Drake Passage between South America and Antarctica. The single major Indian Ocean trench is the Java Trench south of Indonesia.
The cross sections of trenches generally are V-shaped with steeper landward sides. Geophysical data provide important
clues concerning the origin of trenches. No abnormalities in the flow of internal Earth heat or variations in the Earth's magnetic
field occur at trenches. Precision measurements reveal that the force of gravity generally is lower than normal. Small quantities of brown or red clay, which are signs of organic remains, volcanic ash and lapilli, and coarse, graded layers are found in the trench. Large amounts of remains cannot build up because they either are dragged into the Earth's interior or are distorted into folded masses and molded into new material of the continents.
Deep trench in the sea bed indicating the presence of a destructive margin (produced by the movements of plate tectonics). The dragging downwards of one plate of the lithosphere beneath another means that the ocean floor is pulled down. Ocean trenches are found around the edge of the Pacific Ocean and the northeastern Indian Ocean; minor ones occur in the Caribbean and near the Falkland Islands.
Ocean trenches represent the deepest parts of the ocean floor, the deepest being the Mariana Trench which has a depth of
11,034 m/36,201 ft. At depths of below 6 km/3.6 mi there is no light and very high pressure; ocean trenches are inhabited by
crustaceans, coelenterates (for example, sea anemones), polychaetes (a type of worm), molluscs, and echinoderms.
Mariana Trench (depression in the floor of the Pacific Ocean), the deepest seafloor depression in the world. It is located just east of the Mariana Islands in the western part of the ocean basin. The Mariana Trench is an arc-shaped valley extending generally northeast to southwest for about 2500 km ;its average width is about 70 km. The Mariana is one of many deepwater ocean trenches formed by the geologic process of subduction near its southwestern extremity, about 338 km southwest of the island of Guam, is the deepest point on earth. This point, the Challenger Deep, is estimated to be 11,033 m deep. The Challenger Deep was named after HMS Challenger II, the vessel of those who discovered the point in 1948.
In January 1960 Swiss ocean engineer Jacques Piccard and United States Navy Lieutenant Donald Walsh descended into the Challenger Deep...
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