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Volcano - Where Volcanoes Develop, The Origin Of Magma, Types Of Volcanic Eruptions, Different Kinds Of Volcanic Structures

viscosity viscous pressure active

A volcano is an opening in Earth's surface through which molten rock, hot gases, and rocks are ejected. Volcanoes create new land and islands. They can also produce economically important mineral deposits, fertile soils, and beautiful landscapes. However, volcanoes can also destroy lives and property. Therefore, they constitute significant geologic hazards in many parts of the world.

With regard to the hazard that they present, volcanoes can be classified as active, dormant, or extinct. Active volcanoes are those that have erupted within recorded history. Dormant volcanoes are those that have not erupted during recorded history but may erupt again, whereas extinct volcanoes are those for which there is little or no chance of future eruptions.



Controls on the explosivity of volcanic eruptions

Generally, the viscosity of a magma controls the type and violence of eruptions. Viscosity is the resistance of a fluid to flow. The more viscous the magma, the more explosive its eruption is likely to be. Very viscous magmas tend to resist eruption, and so gas pressure builds within the magma pipe leading to the volcanic vent. By the time sufficient pressure builds to displace a viscous magma, the force released by the eruption will be much greater than for a fluid magma. This leads to explosive eruptions. The most important controls on viscosity are the silica content of the magma and its temperature. Basaltic (mafic) lavas are very fluid due to their low silica content. Conversely, rhyolitic lavas are very viscous due to their high silica content. Magma and lava viscosity is also a function of temperature; therefore, a the viscosity of a lava flow will increase as its temperature decreases.

Volatile substances are elements or compounds—hydrogen sulfide, water, carbon dioxide, radon, and other gasses—that escape during eruptions. The Latin root for volatile means "winged." Volatile compounds in magma can cause violent explosive eruptions.


Calderas

The most violent large volcanic eruption is the collapse of a composite volcano. This normally happens on the active margins of tectonic plates, that is, at subduction zones or along a continental rift valley (where a continent is breaking apart). The process is part of the evolution of a composite volcano, which starts with a reservoir of molten rock, several miles wide and under high pressure. This magma rises in the earth's crust and forces its way to the surface. A composite volcano is born in clouds of ash, supersonic steam explosions filling the air with hot rock, ash, and various gases.

After a series of eruptions, perhaps over millions of years, the volcano forms a mountain of lava and pyroclastic material as much as 2-3 mi (3-4 km) high. Eventually, there is one last eruption of ash and pyroclastic flows. The magma begins to boil, gas bubbles expand the magma to many times its original volume, and it explodes upward. The magma chamber rapidly empties its contents onto the landscape above and the volcano collapses into the void, forming a depression known as a caldera.


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over 8 years ago

How And Why Do Volcanoes Develop?

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over 2 years ago

How and why do volcanoes are developed?
As we know about the earth's interior structure which contains different layers:
Core: solid inner core and liquid outer core
Mantle: lower mantle(solid) and upper mantle (molten or we can say semi solid)
and finally the Crust: continental crust and oceanic crust.
Since the crust lies over the underlying upper mantle which is in molten state. Due to convection currents of heat it exerts the pressure to the overlying crust. When such a pressure crosses the limit it (magma) starts erupting resulting the development of Volcanoes.
Also, Have you realized ever why volcanoes are developed in nearer or in the oceanic sides?
It is because thickness of oceanic crust is about 5-10 km and the difference between its density and that of underlying magma is not much higher. As a result eruptions are mostly occurred in the oceanic crust not in the continental crust which has a thickness of about 40 km even more higher near the Himalayas.

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over 4 years ago

If a volcano is extinct I don't think there is any possibility of it occurring in the future. This is because we initially divided volcano into three categories. And if it is so, then extinct volcanoes may not occur in the future at all because it has gone extinct. This can rather be a dormant volcano. What do you think?

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over 4 years ago

If a volcano is extinct I don't think there is any possibility of it occurring in the future. This is because we initially divided volcano into three categories. And if it is so, then extinct volcanoes may not occur in the future at all because it has gone extinct. This can rather be a dormant volcano. What do you think?

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almost 5 years ago

the page is educating, it has most of the topics needed in geogology

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about 6 years ago

where are the answers where volcanoes may form if type that in dont you expect that to come up

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over 6 years ago

volcano can develop in 2 different ways..whats the answer

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over 8 years ago

what are he diffrent kinds of volcanoe?