Explosive/ Effusive Volcanism
...olved gasses in magma the more explosive the emission will be. When explosive volcanoes erupt they produce a large area of gas that is exploded into the atmosphere along with pieces of extremely hot rocks. The sudden cooling produces these hot rocks and shattering of molten rock as it loses its dissolved gases. Explosive volcanoes have a liquid that looks like lava, but it is the melted rock of the volcano. This liquid also flows down the side of the mountainside, but it is not as thick as molten lava. Because of its density the volcano liquid can roll down the slopes of mountainsides at speeds of over one hundred miles per hour. Types of explosive volcanoes are composite cones, calderas and lava domes. Most composite cones are located in a relatively narrow zone that rims the Pacific Ocean called the Ring of Fire. Calderas can be found in Oregon, Hawaii and Yellowstone National Park. Lava Domes can be found in Mount. St. Helens and Yellowstone National Park. The usual rock produced by explosive volcanoes is a white shiny rock with many crystals and often many bubble holes inside, rhyolite. Explosive volcanoes also produce andesites, which are light gray and usually have large box-shaped crystals called plagioclase. A very widely know explosive volcano is Vesuvius. In 62 A.D. a earthquake shook the volcano. In 79 A.D. eruptions began. For the first twelve hours, fine-grained ash and coarse white pumice covered the area, later gray pumice fell. Explosions created avalanches of rock, ash and gases. In less than 24 hours the city of Pompeii and more than 2,000 of its residents perished. When an explosive volcano erupts there is not preparation time to evacuate. When an effusive volcano erupts, it erupts in fountains from the summit or as curtains of fire from large fissures which split the volcanoes sides. These vents allow the lava, which is like a lake of fire, flow down the volcanoes slopes. Effusive volcanoes are usually found close to oceans or seas, because when an effusive volca...