Trenches are formed by subduction, and typically, subduction zones occur around the edges of oceans.
According to the National Geographic, when the leading edge of a dense tectonic plate meets the leading edge of a less-dense plate, the denser plate bends downward. This pace where the denser plate subducts is called a 'subduction zone'.
Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. These trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones.
Ocean trenches occupy the deepest layer of the ocean, the 'hadalpelagic zone'. The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth.
Learn more about ocean trench at the National Geographic.
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