Why do volcanoes often form in arcs near ocean edges?
Quick Answer
Because one tectonic plate sinks beneath another at subduction zones, releasing water and other volatiles that help melt mantle rock. The rising magma creates chains of volcanoes in curved arcs.
The Full Story
Volcanic arcs are most common where an oceanic plate dives beneath another plate. As the descending slab heats up, it releases water into the overlying mantle wedge, lowering the melting point of the rock and generating magma. That magma rises and feeds volcanoes in a long curved belt parallel to the trench offshore. The Andes and the volcanoes of Japan and Indonesia are classic examples. These arc volcanoes often erupt explosively because their magmas can trap gases and become more viscous as they evolve.
Key Facts
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"Why do volcanoes line up in curved chains around the Pacific?"
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