Tremendous forces are at work below the earth's surface. Sometimes they make the ground rumble and shake. Other times they make mountains explode, spewing forth rock, gases, and lava. These mountains are called volcanoes. They are among nature's most spectacular creations--and one of its most dangerous. David L. Harrison takes us on a fascinating voyage beneath the earth's surface to show how volcanoes are created and why they erupt. From its hot, solid iron core, up to the earth's crust, he introduces us to magma, lava, the colliding plates that cause earthquakes, and other natural phenomena. With vivid illustrations by Cheryl Nathan, here is a look at how volcanoes work.