Jennifer Richman, age 8, of Guilderland, N.J., for her question:

 HOW LONG DOES IT TAKE A VOLCANO TO ERUPT?

A volcano likes to catch everybody by surprise. Sometimes it erupts again and again. This may go on for five years or even for a hundred years. Then it takes a rest  but nobody can guess how long it will stay quiet. It may erupt again the next year, or it may wait more than a thousand years. At the end of life, it goes to sleep and never erupts again.

There are hundreds of volcanoes in the world. But no two are exactly alike. Some erupt from the ground and keep erupting for five or 10 years. By then they have built a pointed mountain and maybe never erupt again. Some types keep small eruptions going all the time. Others stay quiet for thousands of years, then burst forth with a huge eruption that lasts a few days or a few weeks.