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A volcano is a hole in the Earth from wich molten rock (magma) and gas erupt. The molten rock that erupts from the volcano (lava) forms a hill or mountain around the hole. The lava may flow out as a viscous liquid, or it may explode from the hole as solid or liquid particles.
Volcanoes can be on different places.
Most of the world\'s volcanoes are found along the margins of huge plates into which the Earth\'s crust is divided . The largest volume of volcanic material is formed at Seafloor Spreading centers between plates, such as the Mid-Atlantic Ridge. These mid-ocean ridges are usually shield volcanoes and erupt quietly onto the ocean floor. In contrast, the volcanoes formed over subduction zones, in regions of plate convergence, may be among the most violent. Along continental margins, chains of volcanoes such as the Andes have formed. Collisions of oceanic crust produce island arcs such as the Antilles, the Aleutians, and the Japanese Islands. In addition to these plate margin areas, volcanoes also form over \"hot spots\" within a plate, as in the cases of the Hawaiian Islands and the Yellowstone volcanic field.
Volcanoes can be active ,dormant and extinct.Active are when they regularly erupt. Around the world, there are abouth 800. A dormant volcan is one, which is sleeping. This volcanoes can be active again.A volcan is extinct ,when it never can erupt again.
There are a lot of types of volcanic eruption.
A volcano may exhibit different styles of eruption at different times, and eruptions may change from one type to another as the eruption progresses.Vulcanian eruptions are characterized by viscous magmas that form short, thick flows around vents; very viscous or solid fragments of lava are violently ejected from these vents.
The most volcanoes with fluid magmas are erupted quietly and flow from the vent to form gently sloping shield volcanoes.These volcanoes are mostly abuoth hot spots, places, were the magma is
so hot, that it melts a hole into the crust. The lava flows from shield volcanoes are usually only 1 to 10 m (3.3 to 33 ft) thick, but they may extend for great distances away from the vent. The volcanoes of Hawaii and Iceland are typical shield volcanoes.
Magmas with high gas contents and high viscosities are usually more explosive than those flowing from shield volcanoes. These gas-rich magmas in many instances are blown high into the air during an eruption. The magma falls as volcanic bombs, which accumulate around the vent and form steep-sided but relatively small cinder cones. Volcanic bombs range in size from fine-grained ash to house-size blocks. Cinder cones most commonly consist of volcanic fragments anywhere from ash to small-pebble size, less than 3 cm (1.2 in) in diameter.
Strombolian eruptions are characterized by moderately fluid lava flows, usually accompanied by a violent lava-fountaining that produces an abundance of volcanic bombs and cinders.
The most violent eruptions, such as that of Washington\'s Mount St. Helens in 1980, are termed Plinian after Pliny the Elder, who died in the Vesuvius eruption of AD 79 . They include the violent ejection of large volumes of volcanic ash, followed by collapse of the central part of the volcano (caldera collapse).
But what comes out of volcanoes? It\'s magma.
Magma is a complex, mobile mixture of crystals, rock fragments, liquid, and gases deep within the Earth.
Volcanoes can make a lot of damage.
In AD 75 the volcano Vesuvian destroyed the well know city Pompeii.Pompeii was founded in the 8th century BC by the oscans, an italic tribe.The city was controled by the romans, when there was an earthqake in AD 62.In that time, it had abouth 20000 inhabitants and was 66 ha. big. Then at Aug. 24th 79 vesuvian erupted explosively. The volcan buried Pompeii, Herculaneum and some other towns under his ash.This eruption killed abouth 2000 people. The others could flew in the sea. Pompeii had been unearth in the yaer 1748. Today the ruins of this city are a famous sightseen.Vesuvian is still active. The last eruptions were in the yaers 1631, 1872, 1906 and 1944.When vesuv would erupt today, it would destroy Rome.
But you should not be afraid, because there are no volcanes in Austria.
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