Kinds of Volcanoes

            Volcanoes have been divided into three main groups by scientists.  They are shield volcanoes, cinder cones, and composite volcanoes.  The material of the volcano as well as the shape define these groups.

          When a large amount of free-flowing lava spills from a vent and spreads along a large area, it creates shield volcanoes.  The lava slowly builds a broad, low, dome shaped mountain.  Mauna Loa is a shield volcano.

          When tephra, solid materials ejected into the air during an eruption, erupts from a vent and descends back to the earth, it creates cinder cones.  The tephra forms a cone-shaped mountain.  Western Mexico’s Paricutin is a well-known cinder-cone volcano.

          When tephra and lava erupt from a vent that is central, it creates composite volcanoes.  Around a towering, cone-shaped mountain, the materials pile in alternate layers behind the vent. 

          The magma chamber of a cinder cone, shield volcano, or composite volcano can occasionally become almost empty.  When this happens, the magma of a volcano erupts onto the area around it.  When it becomes empty, it can no longer support the volcano above it.  The result is the volcano collapses.  It forms a huge crater called a caldera.