VOLCANO-ज्वालामुखी

The eruptions from inside the earth are known as volcanoes. Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater.

Magma – The  material inside the earth.                                                                      

Lava – Magma which comes out is known as Lava.                                                                                            

Vent – That tube from which the Magma moves up is known as vent.                                                                                                                                                       

Crater – The broader opening of the vent through which magma comes out is known as crater.

The Lonar lake was initially believed to be of volcanic origin, but now it is recognized as an impact crater created by the hypervelocity impact of either a comet or a meteorite.

Types of Volcano-

1)Active Volcano–

 It is activated constantly and lava comes out. For e.g. Catapaxi (Equadoor), Etna(Italy)-Straboly(Italy)

2)Dead Volcano –

No lava eruption takes place through it for e.g. poppa volcano at Burma.

3)Dormant Volcano –

Lava eruption after a certain period. e.g. KrakotaJava (Indonesia).Visuvis(Italy)

Types of Volcanoes

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.

1-Fissure volcanoes-

A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity

In Fissure Volcanoes  lava flows that can travel great distances.

2-Shield Volcanoes-

They are known as shield volcano because they resemble a warrior’s shield .

Where a volcano produces low viscosity, runny lava, it spreads far from the source and forms a volcano with gentle slopes: a shield volcano.

Most shield volcanoes are formed from fluid, basaltic lava flows.

They extend to great height as well as distance.

They are the largest of all volcanoes in the world as the lava flows to a far distance. The Hawaiian volcanoes are the most famous examples.

Mauna Kea and Mauna Loa are shield volcanoes.

They are of low explosive in general, but if somehow water gets into the vent they may turn .

3-Composite Volcanoes:

Composite is a cone-shaped volcano built from several layers of lava, ashetc.

 Due to its viscous lava, a composite volcano tends to form tall peaks rather than rounded cones. Mount Fuji in Japan 

Why known as Composite?

Composite volcanoes because they consist of variety of material that include ash, blocks of various stones, pumice, and lava

Shape Cone shaped with moderately steep sides and sometimes have small craters in their summits.

They are characterized by the eruption of a cooler and more viscous lavas than basalt.

These volcanoes often result in explosive eruptions.

This material accumulates in the vicinity of the vent openings and leading to the formation of layers, and this makes the mount appears as composite volcanoes.

4-Caldera:

5-Flood Basalt Provinces-

A flood basalt / plateau basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava.

 Many flood basalts have been attributed to the onset of a hotspot reaching the surface of the earth via a mantle plume.

 Flood basalt provinces such as the Deccan Traps of India are often called traps, meaning "staircase" .

6-Mid-Ocean Ridge Volcanoes

These volcanoes occur in the oceanic areas.

There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.

The mid-ocean ridge consists of thousands of individual volcanoes or volcanic ridge segments which periodically erupt. Beneath a typical mid-ocean ridge, mantle material partially melts as it rises in response to reduced pressure.

Ex- Mid-Atlantic Ridge,

The central portion of this ridge experiences frequent eruptions.

World’s Maximum volcanoes are found at Ring of Fire in pacific ocean.

 Highest active volcanic mountain is cotopaxi.

Largest volcano is Monalia at Hawaii island.

Advantages of volcano

Precious metals come out * Fertile soil also comes out* Islands are found like Andaman &Nicobar islands.

Large volconic eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere).

Disadvantages of volcano

Large  volconic eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere).  Historically, volcanic winters have caused catastrophic famines.

The concentrations of different volcanic gases can vary considerably from one volcano to the next.

Advantages of volcano

Precious metals come out * Fertile soil also comes out* Islands are found like Andaman &Nicobar islands.

Large volconic eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere).

Disadvantages of volcano

Large  volconic eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere).  Historically, volcanic winters have caused catastrophic famines.

The concentrations of different volcanic gases can vary considerably from one volcano to the next.

Gases released in Volcano-

Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide  and sulfur dioxide. Other principal volcanic gases include….hydrogen sulfide, hydrogen chloride, and hydrogen fluoride.