Composite volcanoes are created by felsic magma, which is viscous. The viscous lava cannot travel far down the sides of the volcano before it solidifies, forming the steeply sloping sides that are characteristic of composite volcanoes. Viscosity also causes some eruptions to explode as ash and small rocks. As a result, composite volcanoes consist of alternating layers of ash and lava that has solidified to form rock. The layers form the classic cone shape of composite volcanoes.     Shield volcanoes get their name from their shape. They are literally shaped like a shield. The sides of a... Show more

Composite volcanoes are created by felsic magma, which is viscous. The viscous lava cannot travel far down the sides of the volcano before it solidifies, forming the steeply sloping sides that are characteristic of composite volcanoes. Viscosity also causes some eruptions to explode as ash and small rocks. As a result, composite volcanoes consist of alternating layers of ash and lava that has solidified to form rock. The layers form the classic cone shape of composite volcanoes.    
Shield volcanoes get their name from their shape. They are literally shaped like a shield. The sides of a shield volcano are not steep, but the volcano may cover a very large area. The lava that creates a shield volcano is mafic and not viscous, so it flows easily. The lava can flow over a wide area before it solidifies. This is what creates the broad shield shape. The low viscosity of the lava also means that shield volcano eruptions are effusive rather than explosive. As a result, the layers of shield volcanoes are usually very similar in composition.    

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