The three main types of volcanoes are composite, shield and cinder cone volcanoes. Each type of volcano is formed a different way and possesses specific characteristics indicative of its type.
Composite volcanoes, also called stratovolcanoes, consist of lava flows that are mixed with sandy layers of volcanic rock. These large volcanoes span tens of miles in diameter and tower thousands of feet high, but they have small craters at their summits.
Cinder cone volcanoes are made mainly of cinders, small grainy pieces of volcanic rock; these volcanoes don't have much lava. Cinder cones are smaller volcanoes, usually a thousand feet in height and measuring a mile across.
The largest volcanoes are the shield volcanoes, which reach hundreds of miles in diameter and thousands of feet in height. The islands of Hawaii are actually shield volcanoes lying in the ocean. Shield volcanoes are comprised mainly of frozen lava and have large summit craters.