Kerri Hove, age 10, of Perry, Mich., for her question:

How is a volcano made?

The trouble starts many miles down below the ground. Nobody has been down there to see how a volcano actually gets started. All we can do is try to make a sensible guess. Most experts suspect that the trouble starts below the earth's crust, which varies from five to 40 miles in thickness. Volcanos seem to happen in places where there are deep cracks, right through the crust.

The cracks in the earth's crust tend to scratch and rub each other and in some places they pull apart. Sometimes they shove together and form mighty mountains. Things are very hot down there, and the restless crust makes things hotter. Sometimes the heat melts the solid rocks and forms a buried pocket of lava called magma. If there is a crack to the surface, a volcano may form. Then the seething lava erupts, somewhat like the fizz of a pop bottle.