Volcanoes are one of nature's great wonders. For years they can stand dormant, but once active they can erupt in tremendous explosions of power. Some eruptions are so big, they change the earth's climate. Luckily, geologists can now approximate when an eruption will occur. What are the causes of an eruption and what are the warning signs? Read and find out!

Franklyn M. Branley was the originator of the Let's-Read-and-Find-Out Science series and the author of close to 150 popular books about scientific topics for young readers of all ages. He was Astronomer Emeritus and former Chairman of the American Museum of Natural History-Hayden Planetarium.