What dictates the distance, or arc gap, between the trench and the volcanic arc?

Answer

The dip angle of the subducting slab

The angle at which the slab descends into the mantle influences where the melting zone is located relative to the overriding plate, thereby controlling the distance between the trench and the arc.

What dictates the distance, or arc gap, between the trench and the volcanic arc?

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BEHIND THE SCIENCE 2011 | Subduction Zone Volcanoes

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