Most volcanoes form at the boundaries of Earth's tectonic plates, which are huge slabs of crust and upper mantle that fit together like puzzle pieces. Think of these plates as massive rafts floating ...

Covers how volcanoes are formed, and treats them in historical and mythological perspective, with attention to Mt. St. Helens, Mt. Rainier, and volcanoes in Hawaii. Has a segment on the Modoc people ...

The explosiveness of a volcanic eruption depends on how many gas bubbles form in the magma—and when. Until now, it was thought that gas bubbles were formed primarily when the ambient pressure dropped ...