Composite volcanoes, also known as stratovolcanoes, are formed by the gradual deposition of alternating layers of volcanic lava and ash. When volcanoes erupt, emitting lava that flows very slowly, the lava cools and hardens, forming conical shaped composite volcanoes after multiple eruptions over a span of hundreds of years.
Composite cones are formed by the most common type of magma called andesite. These composite volcanoes form in chains tens of kilometers long and can have heights up to 3,000 meters. The most popular example of a composite volcano is Mount Vesuvius, whose eruption destroyed the Italian town of Pompeii in 79 A.D.