The word "volcano" comes from the name of the Roman god of fire Vulcan.
The science that studies volcanoes - volcanology, geomorphology.
Volcanoes are classified by form (thyroid, stratovolcanoes, cinder cones, domes), activity (active, dormant, extinct), location (surface, underwater, subglacial), etc.
Volcanic activity
Volcanoes are divided according to the degree of volcanic activity on existing, dormant, extinct and dormant. Active volcano is considered to be a volcano erupted in the historical period of time or in the Holocene. The concept of an active rather inaccurate, since the volcano with active fumaroles, some scientists refer to the active, and some to the extinct. Dormant volcanoes are considered non-performing, which may eruption, and extinct - in that they are unlikely.
However, among volcanologists no consensus about how to define an active volcano. Period of volcanic activity may last from several months to several million years. Many volcanoes exhibit volcanic activity several thousand years ago, but now are not considered valid.
Astrophysics, in historical perspective, consider that the volcanic activity is caused, in turn, tidal action of other celestial bodies, may contribute to the emergence of life. In particular, it volcanoes contributed to the formation of the Earth's atmosphere and hydrosphere, released significant amounts of carbon dioxide and water vapor. Scientists also say that too active volcanism, such as on Jupiter's moon Io, can make the surface of the planet uninhabitable. At the same time, the weak tectonic activity leads to the disappearance of carbon dioxide and sterilize the planet. "These two cases represent potential habitability of planets and boundaries exist along with traditional areas of life parameters for systems of low-mass main sequence stars," - the scientists say.
Types of volcanic postroek25
In general, the volcanoes are divided into linear and central, but this division is arbitrary, since the majority of volcanoes are confined to linear tectonic disturbances (faults) in the earth's crust.
Linear volcanoes or volcanoes fractured have extended feeders associated with a deep split bark. Typically, these cracks of basalt flows liquid magma that spreading out to the sides, forming large lava covers. Along cracks appear gentle shafts spray wide flat cones, lava fields. If the magma is more acidic composition (higher silica content in the melt) is a linear shafts and extrusive arrays. When there is an explosive eruption, there may be explosive ditches stretching for tens of kilometers.
The volcanoes of the central type have a central inlet channel, or mouth, leading to the surface of the magma chamber. Muzzle end with the extension, the crater of which, with the growth of volcanic construction moves up. In central volcanoes are the side, or parasitic, craters, which are located on the slopes and are confined to a ring or radial fractures. Often there are lakes in the craters of molten lava. If the magma is viscous, the image of the dome squeezing that clog vents, like the "traffic jam", which leads to the strongest explosive eruptions, when the flow of gas literally knocks the "plug" from the vents.
Forms of central volcanoes depend on the composition and viscosity of the magma. Hot and thin, basaltic magma creates vast and flat shield volcanoes (Mauna Loa, Hawaii). If the volcano is spewing lava periodically, the pyroclastic material, there is cone-shaped layered construction, stratovolcano. The slopes of the volcano are usually covered by deep ravines radial - barranco. The volcanoes of the central type may be purely lava or volcanic products form only - scoria, tuff formations, etc., or to be mixed - stratovolcanoes.
Distinguish between monogenic and polygenic volcanoes. The first resulted from a single eruption, the second - multiple eruptions. Viscous, acid composition, low-temperature magma, squeezing out the vent, forming extrusive dome (needle Mont Pelee, 1902).
Additionally, there are large calderas negative landforms related to subsidence under the weight of volcanic material izvergnuvshegosya and lack of pressure at the depth encountered during unloading of the magma chamber. Such structures are called volcano-tectonic depressions, depressions. Volcano-tectonic depressions are very widespread and is often accompanied by the formation of thick layers of ignimbrites - felsic volcanic rocks with different genesis. They are formed by lava or baked or boiled tuffs. They are characterized by lenticular separation of volcanic glass, pumice, lava and tuff called fyamme tofovidnaya structure or bulk. As a rule, large amounts of ignimbrites associated with shallow magma chamber, formed by melting and replacement of host rocks. Negative landforms associated with central volcanoes, calderas are - major failure of round shape, with a diameter of a few kilometers.
Post-volcanic phenomena
After the eruption, when the activity of the volcano, or terminated for good, or it is "asleep" for thousands of years, on the volcano and its surroundings remain the processes related to the cooling of the magma chamber and called the post-volcanic. These include fumaroles, thermal baths, geysers.
During eruptions sometimes the collapse of volcanic structures to form a caldera - a large basin with a diameter of 16 km and a depth of 1000 m ascent of magma external pressure decreases, the associated gas and liquid products erupt to the surface, and there is an eruption of the volcano. If you are carried to the surface of ancient rocks, not magma and gases prevails among water vapor formed during heating of groundwater, it is called the phreatic eruption.
Risen to the surface lava does not always go on this surface. It only picks up the layers of sedimentary rock and freezes in a compact body (laccoliths), forming a kind of system of low mountains. In Germany, such systems are of Rennes and Eiffel. At the last observed another phenomenon in the form of post-volcanic lakes that fill the former volcanic craters, which failed to form typical volcanic cone (called maars).
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