What makes a volcano explode?
Ben and Greg, Grade 2
Dear Ben and Greg,
Volcanoes explode because the liquid rock (magma or lava) that makes them
contains gas. The gas is dissolved in the magma when it is under
pressure. When the pressure is removed (by the magma moving close to the
surface or by the volcano falling apart, like Mount St. Helens did in
1980) the pressure of the expanding gas is greater than the weight of the
overlying rocks and the gas blows the rock (and magma) out of the way .
It's sort of like the bubbles of gas in a bottle of soda. Before you
open the soda you don't see many bubbles because the pressure in the
bottle keeps the gas dissolved in the soda. When you open the bottle the
pressure is released and the gas bubbles leave the soda. If you shake up
the bottle first, the soda gets pushed out by the bubbles of gas as they
rush out. You might try this, but do it outside.
Thanks for your question.
Steve Mattox, University of North Dakota
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