What is an Ocean Trench?

Mary McMahon
Mary McMahon

An ocean trench is a geological structure which occurs undersea along the boundary of a tectonic plate. Specifically, ocean trenches form along subduction zones, in areas where one plate is being sucked under another. The largest of these trenches are in the Pacific Ocean, where numerous active subduction zones have been identified, but smaller trenches can also be seen in the Indian and Atlantic Ocean. One could consider an ocean trench a sort of undersea valley.

Subduction zones create ocean trenches when one tectonic plate moves beneath another.
Subduction zones create ocean trenches when one tectonic plate moves beneath another.

Oceanic trenches, as ocean trenches are sometimes called, are deep depressions in the Earth's crust, and they comprise the deepest part of the ocean. To think about the way in which ocean trenches form, it may help to have a visual aid; imagine sliding one hand under the other, and think about the trench which forms in the area where the hands meet. This miniature trench is identical to the trenches which are formed in subduction zones. New material to be pulled under is constantly generated at oceanic ridges, where the seafloor is constantly spreading with fresh infusions of rock from beneath the Earth's crust.

Ocean trenches are most often located parallel to volcanic islands.
Ocean trenches are most often located parallel to volcanic islands.

The deepest ocean trench is the Mariana Trench, in the Western Pacific Ocean. Numerous other trenches criss-cross the Pacific, and appear along the edge of South America. In some cases, ocean trenches have become filled with sediment, in which case they are not readily identifiable as trenches, although investigation with radar and other imaging tools can reveal the underlying structure of the trench.

A large ocean trench off the coast of Chile harbors many unique fish.
A large ocean trench off the coast of Chile harbors many unique fish.

Typically, ocean trenches are close to areas of volcanic activity, because volcanoes are very common in subduction zones. The incredible depth of ocean trenches can also create a unique habitat which houses unusual ocean animals which prefer deep water; off the coast of Chile, for example, the fishing is quite good, thanks to a large ocean trench which is present in this area. The depths of an ocean trench pose some very interesting challenges to marine animals, as trenches are extremely dark and very cold, and the pressure of the overlying seawater is intense. Organisms which have adapted to this environment have some rather remarkable traits.

Exploring and mapping ocean trenches has posed some challenges to humans. People are not capable of handling the dark, cold, high-pressure environment of trenches, and the bulk of exploration has been performed with imaging equipment and robotics. People have descended into the Mariana Trench in specially-equipped submarines, but they haven't stayed long.

Ocean trenches compromise the deepest part of the ocean.
Ocean trenches compromise the deepest part of the ocean.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

anon302718

How do animals in trenches survive?

anon241409

I love this website because it's safe and educational. I think that there are over 20 trenches in the ocean. Maybe more! --bird2323

anon79176

This site is the best for my kids.

anon66830

I really love this website. My kids use it all the time for their reports in Earth science class. I would like to thank whoever made this website!

anon64340

What animals live in the trenches?

anon38524

How are they formed?

anon29362

Are there animals living in the trenches?

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