(Fig. 2.4) Composite Volcano.

     Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments.  This is the reason they are called composite.

     Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume.

     Between eruptions they are often so quiet they seem extinct.  To witness the start of a great eruption requires luck or very careful surveillance.

     Composite volcanoes usually erupt in an explosive way.  This is usually caused by viscous magma.  When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.

     Although strato-volcanoes are usually large and conical, we can distinguish different shapes of them: concave (like Agua), pyramidal (like Stromboli), convex-concave (like Vesuvius), helmet-shaped (like Mount Rainier), collapse caldera (like Graciosa), nested (like El Piton in Teide), multiple summits (like Shasta), elongated along a fissure (like Hekla).

(Fig. 2.5) Different Shapes of Composite Volcanoes.

     Strato-volcanoes are constructed along subduction zones.  Examples of composite volcanoes include Mount Hood, Mount Rainier, Mount Shasta, Mount Fugi, Mount Mayon, and Vesuvius.