Dorothy Johnson age 11, of Tucson, Arizona, for her question:

How does a volcano get started?

Most of the world’s volcanoes burst forth in regions where mountains are being made. Here, we know, the crust of the earth is unbalanced and out of kilter. The crusty layers push up into humps and dip down into valleys. The disturbance which causes these things to happen is far, far below the surface of the earth. The roots of a volcano are also way down, perhaps 30 miles or more below the surface, and they seem to occur where deep unrest causes the surface to push up and form mountains.

The roots of a volcano reach down into a pool of molten rock called magma. It is an area of great stresses and strains and from time to time the molten lava boils up and over the surface. When this happens, we have a full fledged volcanic eruption.