How Does a Volcano Form?

By Staff WriterLast Updated Mar 29, 2020 3:14:59 AM ET
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A volcano forms when a vent in the Earth's crust allows magma to well up from below. The magma fills a void underneath the surface, and when it builds up enough pressure, it bursts through to the surface. As the magma cools, it hardens into rock, and multiple eruptions may build up the mountainous form of a volcano.