What Causes An Ocean Trench?

Ocean trenches are the deepest part of the ocean floor and the part of the Earth’s surface that is closest to the center of the earth. This makes them unique and quite interesting to oceanographers, geologists and other scientists.

Studies by geologists and earthquake experts show that trenches are usually formed at specific places on the Earth’s crust. The crust of the earth, which is several miles thick, is not one solid piece. It is made up of numerous separate pieces called plates. Trenches have formed when two plates come into contact and the denser of the two sinks below the other plate. The deep line where these two plates have met can form trenches that are hundreds of miles long.

One way to look at trenches in the ocean floor is to think of valleys that we see in hilly or mountainous regions on Earth. The hills and mountains push up but are not close together. The lower areas between the mountains are valleys. Trenches are similar to valleys, though they may be formed in a different way. Both an ocean trench and a mountain valley are created by movement of the Earth’s crust.

Volcanoes are closely associated with ocean trenches, as geological studies have shown. In fact, new submarine technology has allowed video and photographic evidence to be gathered that shows a “volcanic arc” on one side of an ocean trench. These arcs are actually a string of mountains or islands that contain volcanic activity. They stretch over vast areas of the Pacific Ocean, for example.

When the plates meet and one slides under the other, it is likely that magma from deep in the earth can escape. The Mariana Islands in the Pacific and the Lesser Antilles in the Atlantic are good examples of this fascinating geological activity. Scientists have identified at least three different types of plate boundaries, including divergent, convergent and transform. Divergent plate boundaries occur at ridges in the open ocean. Convergent boundaries occur when one plate sinks beneath another and actually goes deep enough to reach the second layer of the Earth, the mantle. In a transform boundary, the plates usually slide past one another.

Studies have shown that trenches are, on average, 2 miles or a bit more beneath the rest of the ocean floor in that area. The deepest trench has been dubbed “Challenger Deep.” It is in the trench of the Mariana Islands mentioned earlier. This trench is several miles below the ocean’s surface. Other recognized ocean trenches are in the region near the South American continent – the Peru/Chile trench is recognized as the world’s longest, the Puerto Rico Trench and the Aleutian Trench, near Alaska.

The science of plate tectonics looks closely at this phenomenon. In fact, the movement of the Eurasian Plate and the Pacific Plate create a zone of “intense earthquake and volcanic activity.” According to this source, the Phillippine Plate is older and more dense than the Pacific Plate and it moves below the Pacific Plate to form the deep ocean trench.

Written by Lucas Beaumont

Generalist. Wikipedia contributor. Elementary school teacher from Saskatchewan, Canada.

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