http://hvo.wr.usgs.gov/kilauea/summary/main.html
What is a Volcano?
A volcano is a mountain with an opening that reaches down into the earth. Sometimes, when pressure inside the earth builds up, a volcano can erupt. An eruption occurs when lava shoots out and spills down a volcano. Lava contains ash, cinders, and hot, molten rock. When the hot lava cools, it gets hard and makes new rock. A volcanic eruption can cause damage and changes to the landscape.