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Supervolcanoes How do supervolcanoes form? Use this information to label your diagrams… 1. Supervolcanoes form at destructive plate margins or over parts of the mantle that are really hot. These are called hot spots. At these points magma moves upwards in the Mantle, hits the base of the earth’s crust and melts it creating a huge chamber of magma. The hot spot is static but the Earth’s crust moves over it. Yellowstone National Park is on top of a hotspot. 2. As the magma rises up through cracks in the earth’s crust it gets stuck and pools, melting the rock around for thousands of years. A magma chamber is formed below the surface and the pressure of the magma causes a circular bulge on the surface. 3. Over thousands of years the pressure builds up and the bulge eventually cracks, creating vents for lava to escape from. The lava erupts out of the vents causing earthquakes and sending up massive plumes of ash and rock. 4. As the eruption continues it drains the magma chamber and the land above collapse down over, creating a caldera. This is a big crater left as a result of the bulge collapsing. Sometimes these get filled with water to form a big lake such as Lake Toba in Indonesia. What are the characteristics of a supervolcano? Supervolcanoes are large depressions, called calderas that are marked by a rim of higher land around their edges. They are very hard to spot at ground level due to their size. The caldera at Yellowstone National Park is close to 100km long, 40km wide and 8km deep. They emit enormous quantities of ash. About 2.1 m years ago the Yellowstone supervolcano erupted 2,500 times more ash than Mount St Helens did in 1980. Supervolcanoes are eruptions and explosions of catastrophic proportions, on the Volcano Explosivity Index (VEI) supervolcanoes are an 8 on a scale that runs from 1 to 8. Each leap up the scale represents an increase of explosive scale of 10 times the power. Mount St Helens was VEI 5! They also affect a much wider area than a normal volcano. The ash would settle over hundreds of square kilometres compared to that from a normal volcano which would cover only a few square kilometres. They also have global impacts. CHARACTERISTICS Normal Volcano Shape Cone-like mountain –especially if it is a composite volcano. Size Etna is 3km high and 140km in its circumference. Scale of emissions Ash can travel a long way, lava travels shorter distances. Impact Over a few km2 Supervolcano