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What is a Volcano? • Volcano-A weak spot in the crust where molten material comes to the surface. Volcano locations • Ring of fire-Major volcanic belt around the Pacific Ocean. (plate boundary) Island Arc-A ring of islands that forms over a plate boundary. Hot spot-An area where a volcano forms in the middle of a continental or oceanic plate when magma melts through the crust like a blowtorch. Types of Volcanoes • Composite = explosive eruptions that release huge amounts of gas and ash. pyroclastic flows and lahars can occur. Can produce dust bombs and blocks. This type is found on continental-oceanic plate boundaries. (ie. Mt. Rainer, Mt. St. Helens, Mt. Hood) Shield = mainly lava flows; (ie. Mt. Kilauea) Cinder Cone = bombs, ash, and cinder are ejected from a volcanic vent and produce a cone.. (ie Sunset Crater, Arizona) Types of Eruptions • Type of eruption is determined by the type of magma in the volcano • Quiet Eruptions – basaltic-thin, runny lava. Explosive Eruptions– • granitic-thick, sticky lava. (It gets stuck, pressure is built, and it explodes) Activity of Volcanoes • Active – is erupting or has shown signs that it may erupt in the near future. Dormant – is sleeping, but scientists expect it to awaken in the future. Extinct – unlikely to erupt again. Structure of a Volcano • Magma-Extremely hot molten material that also includes dissolved gases and including water vapor. • Magma Chamber-A large underground pocket formed as magma rises toward the surface. • Pipe-A narrow almost vertical crack in the crust through which magma rises to the surface. • Vent-Point on the surface where magma leaves the volcano’s pipe. • Side Vent-When magma forces its way out a volcano through the side. • Crater-A bowl shaped area that forms around the volcano’s vent. • Lava-Magma that reaches the surface. • Lava Flow-The river of lava that pours down a volcano and over the land. What comes out of a volcano? Gases-Carbon Dioxide and Sulfur Dioxide are common gases. Steam also comes out. Lava-What magma is called when it reaches the Earth’s surface and loses some of its gas. • Aa-Cool, slow moving lava. • Pahoehoe-Hot, fast moving lava. Blocks-Have sharp corners, are chunks of rock blown out from inside the volcano. Bombs-Masses of lava that cool into rounded shapes before hitting the ground. Cinder-When lava is blown into the air during an eruption, it sometimes cools into small, rough pieces of rock that are puffed up by gas. Pumice-Formed like cinder, but contains more trapped gas. Light enough to float on water. Ash-Lava that has been blown apart by gases into sand-like particles. Dust-The smallest particles of ash Tuff-When ash mixes with rain or other moisture and forms a hard, cement-like rock. Lahar-A hot or cold mixture of water and rock fragments flowing down the slopes of a volcano or river valley. Pyroclastic Flow-A high density cloud that is mixture of hot, dry rock fragments and gas moving away from the vent at high speeds. Temperature is between 200C to 700C. Volcanic Landforms • Dome Mtn. – magma is trapped below a horizontal layer and pushes it into a dome shape and cools. Sill – magma cools horizontally between rock layers Dike – magma cools vertically btwn. rock layers Volcanic Neck - formed when magma cools in a volcanic pipe. Lava plateau – high level area formed by thin, running lava. Batholith – mass of rock formed when a large mass of magma cools below the surface. Caldera – huge hole left by the collapse of a huge volcano. Volcanoes in Space • Mars-Has the largest volcano called Olympus Mons. Around the base of the volcano is a cliff that equals 5 times the size of the Grand Canyon. Volcanoes in Space Venus Has the most volcanoes Moon • Craters are NOT from volcanoes. They are from meteorites smashing into the moon. Lava flows more than 3 billion years ago created smooth dark areas on the moon. THE END???? http://vulcan.wr.usgs.gov/Outrea ch/AboutVolcanoes/framework. html Sept 2006 14 October 2004 http://vulcan.wr.usgs.gov/Outreach/ AboutVolcanoes/framework.html