Jamie Herbert, age 10, of Darien, Connecticut, for his question:

When is a volcano extinct?

A crater filled with calm lake watc r is fairly reliable evidence that the old volcano is finally extinct. When rocks in the cone and crater reveal that there has been no volcanic activity for a few thousand years, it is also likely that the volcano is dead. Earth scientists also consider another feature. Fiery volcanoes are part of fast mountain making projects. After hundreds of millions of years, the region finishes growing and the restless upheavals come to an end. So do the volcanoes that came with the project. If the mountains are fully grown and the volcano's crater has not puffed even a small plume of smoke for 1,000 years or so, earth scientists feel fairly safe in pronouncing it extinct.

We know where eruptions are likely to happen but not exactly when. With more research, future earth scientists will be able to predict these events and warn people in time to escape the disaster areas.