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Oceanic trench

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The Peru-Chile Trench
A picture of the Peru-Chile Trench.

Found at the base of some continental slopes, ocean trenches have relatively steepsides falling dramatically to the ocean floor. In geology, subduction is the theoretical process whereby one oceanic plate slides under another crustal plate. Subduction is believed to work by density. As the heavy plate descends steeply into the earth, the lighter, or less dense, the two plates rides over the edge of the heavier plate. The long, narrow belt produced by this process is called the "subduction zone." It is in these areas that oceanic trenches (linear folds) form that can be approximately 1,500 miles (2,400 km) long, several miles deep, and as much as 70 miles (112 km) wide.

Oceanographers cite at least five trenches that are over 6 miles (10 km) deep. Trenches are active with earthquakes and resulting tsunamis. Most volcanism associated with trench occurs on the continent and not on the seafloor. However, many of the ocean's volcanic islands and seamounts are found in what are called "island arcs," bending chains of islands rising from the sea floor, usually paralleling the concave edges of an oceanic trench. The western Pacific has island arcsm as do the Aleutian Islands.[1]

Near the island of Guam is the famous Mariana Trench located where the Pacific Plate descends under the leading edge of the Eurasian Plate. Measured at 36,201 feet - over 6.8 miles (11 km) deep, this trench is the deepest known spot in any ocean. In 1960, two brave men in the bathyscaph Trieste reached the Mariana Trench - a truly daring accomplishment! Other extensive trench regions around the world include the South Sandwich Trench between South America and Antarctica, the Peru-Chile Trench, and the Aleutian Trench.

  • Shukman, David 2013. Deep ocean undersea vents. BBC News Science & Technology [1].


  1. The Ocean Book, Wonders of Creation