What type of geological activity can lead to explosive eruptions in volcanic arcs?

Explosive eruptions in volcanic arcs are primarily driven by the pressure buildup that occurs at subduction zones. These zones form where one tectonic plate is forced beneath another, often leading to the melting of mantle material and the generation of magma. As the subducting plate descends, it releases water and other volatiles into the mantle, lowering the melting point of the overlying mantle rocks and allowing magma to form.

As this magma rises towards the surface, it can accumulate in magma chambers. Over time, gases and pressure build up within these chambers due to the increasing volume of magma and the solubility of gases under pressure. When this pressure becomes sufficiently high, it can result in a violent explosive eruption as the magma and gases escape rapidly. The presence of water, which is introduced by the subducting oceanic plate, plays a crucial role in the intensity of the eruption, contributing to the explosive nature of the volcanic activity observed in these arcs.

Other geological activities listed, such as caldera collapse, hydrothermal circulation, and oceanic trench formation, either occur as a result of volcanic activity or do not directly lead to explosive eruptions in the same manner as pressure buildup at subduction zones.