What causes a volcano to erupt?

Andrew M. Thornberg

Dear Andrew,

Volcanoes are "born" when magma (liquid rock inside the earth) reaches the surface. Depending on the type and duration of the eruption lava and or tephra can pile up to make a volcano. You might enjoy reading "Birth of Volcanoes" by Maurice Krafft (in Volcanoes Fire from the Earth: Abrams Discoveries, 208 p.).

Volcanoes erupt because of buoyancy and gas pressure. Buoyancy is a force that causes lighter material to rise through surrounding denser material (think of a hot air balloon rising in the cooler air). The hot liquid magma rises towards the surface through the more dense rock. Gas pressure from gas dissolved in the magma also exerts force on the surrounding rock. It cracks the rocks above the magma and then moves into the crack. This process repeats many times until the magma reaches the surface.

Steve Mattox, University of North Dakota

Other Categories        Other Questions
To VolcanoWorld