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Composite Volcanoes
Composite volcanoes are towering structures, such as Mount St. Helen and Mount Fuji. They are constructed from alternating layers of lava flows and pyroclastic materials, such as ash and cinders. This composite structure provides them with the strength to support their steep, concave sides. Composite volcanoes, also known as stratovolcanoes, typically consist of andesite or dacite lava. This type of lava is viscous and slow-moving. It coats the sides of the volcano but rarely extends very far from the base of the volcanic cone. This lava is also highly explosive, due to an abundance of gas trapped within it. Large amounts of ash and clastic materials rain down on the volcano, creating new layers.
Shield Volcanoes
Shield volcanoes are broad, shallow-sloped structures, such as Mauna Loa and Mauna Kea in the Hawaiian Islands. These volcanoes are constructed almost entirely from lava flows, as much as 90 to 99 percent. They are comprised of highly fluid basaltic lava. This lava flows out from central vents in all directions, flowing great distances before solidifying. This flow creates the volcanoes' shield-like, convex shape. These lava flows produce a thin, brittle layer of hardened lava on the surface. However, beneath this covering, channels of fast-flowing lava continue to funnel the hot, fast-flowing lava for great distances.
Cinder Cone Volcanoes
Cinder cone volcanoes, such as Paricutin in Mexico, are much smaller than composite or shield volcanoes. They are constructed of loose volcanic cinders. This tephra material is comprised of fragmented pyroclastic material. It is characterized by lava chunks, not ash, called scoria. These cinders are produced from thick basaltic lava. The gas-rich lava produces short-lived explosive outbursts, known as Strombolian eruptions. These small explosions produce fist-sized fragments of lava that solidify before striking the ground, producing vesicular pieces of lava rock. These rocks pile up around the vent, creating small cones with steep, straight sides. Because of the loose nature of the structure, cinder cone volcanoes often produce basaltic lava flows that leak-out from their base. These flows can cover surrounding areas.
Caldera Volcanoes
Caldera volcanoes, such as the Yellowstone supervolcano, are the most explosive and cataclysmic volcanoes on the face of the planet. These immense volcanoes consist of a huge sub-surface magma chamber filled with rhyolite magma. This magma has a very high concentration of gas, fueling the volcanic explosivity. When these supervolcanoes erupt and empty their magma chambers, the surface over them collapses, forming large, bowl-like calderas. These volcanoes also produce massive eruption columns that pump gasses into the atmosphere and rain-down ash around the planet. Furthermore, their pyroclastic flows can extend for hundreds of miles.