Some of the Earth's grandest mountains are composite volcanoes -- sometimes called stratovolcanoes. They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases. Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, Mount St. Helens and Mount Rainier in Washington.
Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone.
The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.
When a composite volcano becomes dormant, erosion begins to destroy the cone. As the cone is stripped away, the hardened magma filling the conduit (the volcanic plug) and fissures (the dikes) becomes exposed, and it too is slowly reduced by erosion. Finally, all that remains is the plug and dike complex projecting above the land surface -- a telltale remnant of the vanished volcano.
Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite.
Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume.
Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance.
Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.
stratovolcano, also called a composite volcano, is a tall, conical volcano composed of many layers of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from them is viscous, and cools and hardens before spreading very far. The source magma of this rock is classified as acidic, or high in silica to intermediate (rhyolite, dacite, or andesite). This is in contrast to less viscous basic magma that forms shield volcanoes (such as Mauna Loa in Hawaii), which have a wide base and more gently sloping profile.
Although stratovolcanoes are sometimes called composite volcanoes, volcanologists prefer to use the term stratovolcano to distinguish among volcanoes because all volcanoes of any size have a composite (layered) structure — that is, are built up from sequential outpourings of eruptive materials.
...all the best.
2007-03-23 23:20:20
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answer #1
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answered by popcandy 4
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Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite.
Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance.
Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.
Its on land
2007-03-23 22:19:23
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answer #2
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answered by Rico 2
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Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite.
Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume.
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Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance.
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Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.
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Although strato-volcanoes are usually large and conical, we can distinguish different shapes of them: concave (like Agua), pyramidal (like Stromboli), convex-concave (like Vesuvius), helmet-shaped (like Mount Rainier), collapse caldera (like Graciosa), nested (like El Piton in Teide), multiple summits (like Shasta), elongated along a fissure (like Hekla).
They can occur anywhere, land or sea, but always over asubduction zone of the earth's crust.
2007-03-23 22:13:31
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answer #3
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answered by Anonymous
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