: How do Volcanoes work?

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I’ve been alway fascinated by volcanoes, but I’ve never been able to understand how they work. Can somebody help me?

In: Earth Science
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Very simple explanation: lava underground is under a lot of pressure. Sometimes when the tectonic plates move, a weak point is created where the lava can push through, sometimes creating a volcano.

Melts form at areas where a) there’s a significant amount of “hydrated” rock, typically at subducting oceanic plate boundaries b) an area of decreased pressure, like an oceanic ridge, which forms at a divergent rift or c) increased temperatures – like the Hawai’ian island chain which forms over a mantle plume.

Most people would assume volcanoes form from the melt traveling straight up, but melts actually take a more zig-zaggy path, following the structural weak points in the lithosphere. We can see this with plate-like igneous remnants called volcanic dikes. The melt eventually accumulates and forms a magma chamber beneath the future volcano.

Volcanoes will periodically erupt depending on how much silica in the melt. Felsic (silica rich) melts produce more explosive eruptions and also form taller stratovolcanoes, like Mt St Helens or Vesuvius. Mafic (less silica) melts produce gentler sloped volcanoes.

Eventually, the magma chamber beneath the volcano will lack the interior pressure to support the weight above – this is much more common with stratovolcanoes. This causes the volcano to collapse and form a caldera, like Crater Lake.