arc-trench gap

geology

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July 17, 2026

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The arc-trench gap refers to the distance between a volcanic arc and an oceanic trench. This geological feature is a result of plate tectonics, specifically at convergent plate boundaries where one tectonic plate subducts beneath another.

When an oceanic plate subducts, it creates a deep-sea trench. As the subducting plate descends, it heats up and releases volatile components, causing melting in the mantle wedge above. This generates magma that rises to form volcanoes on the overriding plate, creating a volcanic arc. The distance between the trench and this volcanic arc is the arc-trench gap. A narrower gap indicates a steeper subduction angle, while a wider gap suggests a shallower angle. Behind some island arcs, a back-arc basin can form due to extension and seafloor spreading.

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plate tectonics
Island arcs
…the arc, known as the arc-trench gap, depends on the angle of subduction. Steeper subduction zones have relatively narrow arc-trench gaps. A basin may form within this region, known as a fore-arc basin, and may be filled with sediments derived from the volcanic arc or with remains of oceanic crust.
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…the arc, known as the arc-trench gap, depends on the angle of subduction. Steeper subduction zones have relatively narrow arc-trench gaps. A basin may form within this region, known as a fore-arc basin, and may be filled with sediments derived from the volcanic arc or with remains of oceanic crust.
Read More