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+ Volcanoes By: Bekah Richards + Types of Volcanoes + Composite Volcano Sometimes called Stratovolcanoes, Composite volcanoes form when runny lava escapes through a fissure and flows a long way. Composite volcanoes are tall cone-shaped mountains that are typically steeply-sided, symmetrical cones of large dimensions. These volcanoes are built in layers by multiple eruptions, sometimes recurring over hundreds of thousands of years, sometimes over a few hundred. Andesite magma (the most common but not the only magma type), tends to form composite cones. During some eruptions, cinders, bombs and blocks form a mountain or add height to one that earlier volcanic eruptions had built. During other eruptions, lava flows cement these rocks together. Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. + Cinder Cone Volcano Cinder cone volcanoes are the most common kind of volcanoes.They are steep sided cones of basaltic fragments and are smaller and simpler than composite volcanoes. Streaming gases carry liquid lava blobs into the atmosphere that fall back to earth around a single vent to form the cone. The volcano forms when ash, cinders and bombs pile up around the vent to form a circular or oval cone. Most have a bowl-shaped crater at the summit. The longer the eruption, the higher the cone. + Shield volcano Shield volcanoes are large volcanoes that are built almost entirely of fluid lava flows. It has broad sloping sides and is usually surrounded by gently sloping hills in a circular or fan shaped pattern, that looks like a warrior's shield. The volcano is produced by the action of the gas (steam or water vapor) with heat from the earth's core. This action melts rock turning it into magma. The pressure from the heat of the gas pushes the magma upwards till it explodes. Molten magma shoots upward from deep below the ocean floor and breaks through the drifting plates to form shield volcanoes. Lava flows gently and continuously out of the central volcanic vent or group of vents. Shield volcanoes may be produced by hot spots which lay far away from the edges of tectonic plates. Shields also occur along the mid-oceanic ridge, where sea floor spreading is in progress and along subduction related volcanic arcs. + Ash Cloud: very small solid particles ejected from a volcano during an eruption which have intermediate axes Vent: an opening at the earth's surface from which volcanic material, as lava, steam, or gas, is eliminated. Side vent: A volcanic vent is an opening found in the earth's crust through which molten lava, volcanic gases and rocks pass through onto the land surface or into the atmosphere. The lava pours out of fissure vents before making lava channels that drain into the atmosphere. Magma Chamber is a large underground pool of liquid rock found beneath the surface of the earth. The molten rock in such a chamber is under great pressure, and gives enough time, that pressure can gradually fracture the rock around it creating outlines for the magma. If it finds a way to the surface, then the result will be a volcanic eruption; consequently many volcanoes are situated over magma chambers. + Pahoehoe Lava Pahoehoe lava is usually the first kind of lava to erupt from a volcano. The lava that flows from Pahoehoe flows is very, viscous, that means that it is thin and liquid. It has a smooth surface that dries pretty quickly and becomes thicker and flows more slowly than the still hot lava below the surface. As the surface of the flow dries, it turn black and becomes crusty. The top crust is not safe to walk on because it is weak and can collapse. + A’a Lave A'a lava flows have a rough surface made up of broken blocks of lava. These broken pieces of lava are called clinkers. It looks like little lava spines are sticking up from the lava as it moves. The lava is like paste because it is so thick and the clinkers travel on top of the lava flow. Below the top layer of the lava flow there is a core of slow viscous lava. The clinkers are burried by the front of the lava flow as the lava moves. + Lava Pillow Pillow lava forms when lava pours into the ocean. The lava cools fast and makes a ball. As the lava continues to flow it forces an opening in the crust of the pillow and more flows out to form another pillow shape. Pillow lava is made from basalt lava flows that reaches a source of water. Sometimes scientists find pillow lava strings on the land. That helps them to know that an area of land was under water in the past. + Lava Fountain A lava fountain is a large amount of lava that is thrown up into the air when gas bubbles expand in the melted rock. Most lava fountains range in height from 30 to 300 feet. Sometimes the fountain can be as tall as 1,500 feet tall. Lava fountains erupt inside lava lakes, along a fissure, isolated vents or from lava tubes. + Lava Flow: A lava flow is a molten river of melted rock. Lava flows do not come from explosive eruptions, but they just pour out of the top of a vent slowly. Lava flows burn and destroy everything in their paths. How fast lava flows depends on what the lava is made up, how steep the ground is, how much lava is flowing from the vent, and how wide the flow is. Basalt flows are thin enough to flow quickly for a long distance. Lava flows made up of andesite moves very slow and is called viscous because it is very thick. Viscous lava flows so slowly that lava domes can form over the mouth of a vent. Lava Lake: When large amounts of lava pour into a crater a lake of lava is made. Once the lava that has collected in the crater has cooled and dried it is still called a lava lake. Lava Flow And Lava Lake + Bibliography http://www.k12.hi.us/~kapunaha/student_projects/volc_blo wout/shield_volcano.htm www.Wikipedia.com http://www.skybrary.aero/index.php/Volcanic_Ash http://library.thinkquest.org/TQ0311160/vollava.htm