Anne Strole, age 12, of Terre Haute, Ind., for her question:

Do we know how volcanoes form?

These fiery upheavals are caused deep in the rocky layers of the Earth. These low levels are far out of sight, and we know about them only from indirect evidence, such as vibrations from earthquake shocks. In recent years the Earth has been studied by teams of scientists from many nations, and a lot of new data has been assembled. Earth scientists are now rearranging their old ideas about volcanoes and other such dramatic upheavals.

A volcano starts miles below the surface and may be caused by still deeper upsets in the mantle layer below the Earth's crustal layer of rocks. Almost certainly it is caused by deep stresses and strains, such as mountain making. These pressures may cause the friction and heat necessary to turn rock to the molten magma that erupts from a weak spot in the solid crust.