What causes a volcanic eruption?

Question

What causes a volcanic eruption?

Answer 1

A volcanic eruption happens when lava bubbles up to or near the surface of the Earth. What happens next depends on the eruption. If gas builds up, you get something like Mt. St. Helens, and if the lava just flows out you get something more like the volcanoes in Hawaii.

Answer 2

Volcano is an opening in the earth's surface through which lava,hot gases and rock fragments erupt.Such a opening forms when melted rock from deep within the earth blasts through the surface.This blasting occurs when the build-up of pressure in the magma chamber(a reservoir of molten rock which usually exists deep beneath every volcano) forces magma  up a pipe  or vent to the surface where it erupts as lava.