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What happens inside a volcano?

Underneath active volcanoes are magma chambers, containing molten rock (magma). The magma is less dense than the solid rock surrounding it, and so the magma tends to rise to the surface through cracks or conduits in the solid rock.

Sometimes the magma contains large amounts of dissolved gasses. If this is the case, when the magma reaches the surface, the gasses will suddenly come out of the magma, causing pumice and ash to be violently thrown into the air. This type of eruption is not unlike the sudden release of carbon dioxide from a carbonated beverage can that has been shaken up, spewing soda pop foam. Examples include Mt. Saint Helens in the Pacific northwest and Mt. Pinatubo in the Phillipines.

If the magma does not contain much dissolved gas, then it oozes out the sides or top of the volcano and forms lava flows. This is the type of eruption that commonly occurs in Hawaii.


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