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We are discussing here towards Volcano.
A volcano is an opening in the earth’s crust through which lava, volcanic ash, and gases escape. Volcanic eruptions are partly driven by pressure from dissolved gas, much as escaping gases force the cork out of a bottle of champagne. Beneath a volcano, liquid magma containing dissolved gases rises through cracks in the Earth’s crust. As the magma rises, pressure decreases, allowing the gases to form bubbles. How the magma (lava) behaves when it reaches the surface depends on both its gas content and chemical composition. Lavas with low silica contents have low viscosities and flow freely, allowing any gas bubbles to escape readily, while lavas with high silica contents are more viscous (resistant to flow), so that any trapped gases cannot escape gradually.

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(Hindi) Volcano for UPSC CSE

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volcano is an opening in the earth’s crust through which lava, volcanic ash, and gases escape. Volcanic eruptions are partly driven by pressure from dissolved gas, much as escaping gases force the cork out of a bottle of champagne. Beneath a volcano, liquid magma containing dissolved gases rises through cracks in the Earth’s crust. As the magma rises, pressure decreases, allowing the gases to form bubbles. How the magma (lava) behaves when it reaches the surface depends on both its gas content and chemical composition. Lavas with low silica contents have low viscosities and flow freely, allowing any gas bubbles to escape readily, while lavas with high silica contents are more viscous (resistant to flow), so that any trapped gases cannot escape gradually.

Volcano Introduction (in Hindi)

Batholiths
These are large rock masses formed due to cooling down and solidification of hot magma inside the earth.They appear on the surface only after the denudation processes remove the overlying materials.Batholiths form the core of huge mountains and may be exposed on surface after erosion.These are granitic
Laccoliths

These are large dome-shaped intrusive bodies connected by a pipe-like conduit from below.

These are basically intrusive counterparts of an exposed domelike batholith.

The Karnataka plateau is spotted with dome hills of granite rocks. Most of these, now exfoliated, are examples of laccoliths or batholiths.

Lapolith

As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane. It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called Lapolith.

Phacolith

A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country.

Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the Phacoliths.

Sills

These are solidified horizontal lava layers inside the earth.

The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material.

The thinner ones are called sheets while the thick horizontal deposits are called sills.

Dykes

When the lava makes its way through cracks and the fissures developed in the land, it solidifies almost perpendicular to the ground.

It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes.

These are the most commonly found intrusive forms in the western Maharashtra area. These are considered the feeders for the eruptions that led to the development of the Deccan traps.

Intrusive Volcanic Landform (in Hindi)

Extrusive landforms are formed from material thrown out during volcanic activity.
The materials thrown out during volcanic activity includes lava flows, pyroclastic debris, volcanic bombs, ash and dust and gases such as nitrogen compounds, sulphur compoundsand minor amounts of chlorine, hydrogen and argon.
A conical vent is a narrow cylindrical vent through which magma flows out violently. Conical vents are common in andesitic (composite or stratovolcano) volcanism.
A fissure vent, also known as a volcanic fissure or eruption fissure, is a narrow, linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few meters wide and may be many kilometers long. Fissure vents are common in basaltic volcanism.

Extrusive Volcanic Landforms (in Hindi)

Stratovolcano (or composite volcano) — a conical volcano consisting of layers of solid lava flows mixed with layers of other rock.

Cinder cone volcano — doesn’t have any horizontal layers, and is instead a steep conical hill of tephra (volcanic debris) that accumulates around and downwind from the vent.

Shield volcano —  a type of volcano built entirely or mostly from fluid lava vents. They are named like this because when viewed from above, you can see just how massive and imposing they are – like a warrior’s shield.

Conical Vent Cinder Cone: Extrusive Volcanic Landform (in Hindi)

Caldera Lake
After the eruption of magma has ceased, the crater frequently turns into a lake at a later time. This lake is called a ‘caldera’. Examples: Lonar in Maharashtra and Krakatao in Indonesia.
Geyser fumaroles (also called solfataras), and hot springs are generally found in regions of young volcanic activity. Surface water percolates downward through the rocks below the Earth's surface to high-temperature regions surrounding a magma reservoir, either active or recently solidified but still hot. There the water is heated, becomes less dense, and rises back to the surface along fissures and cracks. Sometimes these features are called "dying volcanoes" because they seem to represent the last stage of volcanic activity as the magma, at depth, cools and hardens.

 Eruptinggeysers provide spectacular displays of underground energy suddenly unleashed, but their mechanisms are not completely understood. Large amounts of hot water are presumed to fill underground cavities. The water, upon further heating, is violently ejected when a portion of it suddenly flashes into steam. This cycle can be repeated with remarkable regularity, as for example, at Old Faithful Geyser in Yellowstone National Park, which erupts on an average of about once every 65 minutes.

Volcanic Landform-Crater, Geyser, Caldera (in Hindi)

An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.
An erupting volcano is an active volcano that is having an eruption...
A dormant volcano is an active volcano that is not erupting, but supposed to erupt again.
An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.

Active,Dormant,Extinct Volcano (in Hindi)

There are three volcanic belts, besides many volcanoes which are outside these belts. The three volcanic belts are as under:

1. The Circum-Pacific belt

2. The Mid-Continental belt

3. The Mid-Atlantic belt.

1. The Circum-Pacific belt:

This is the most important belt of volcanoes. This is the so called Ring of Fire. The belt extends through the Andes of South America, Central America, Mexico, the Cascade Mountains of Western United States, the Aleutain Islands, Kamchatka, the Kuril Isles, Japan, the Philippines, Celebes, New Guinea, the Solomon Islands, New Caledonia and New Zealand.

This belt has 80 active volcanoes. The Circum-Pacific belt meets the mid- continental belt in the East Indies. This belt is characterised by high volcanic cones and volcanic mountains. The volcanoes of the Aleutian Island, Hawaii Island and Japan are found in Chains.

Cotapaxi is the highest volcanic mountain (6035m) in the world. Other important volcanoes found in this belt are Fuziyama, Shasta, Rainer and Hood.

In Alaska there is a Valley of Ten Thousand Smokes. It may be pointed out that in this belt volcanic eruptions occur because of the subduction of the Pacific plate below the Asiatic plate.

In Equador, South America, there are about 22 volcanoes out of which 15 are more than 4450 metres above the sea level. Besides, other high volcanic mountains are St. Helens (Washington, U.S.A.), Kilavea (Hawaii Island, U.S.A.), Mt. Taal, Pinatubo and Mayon (Philippines). It may be mentioned that the volcanoes of Hawaii Island are situated in the intra- plate region.

2. The Mid-Continental belt:

This belt has various volcanoes of the Alpine mountain chain, Mediterranea Sea (Stromboli, Vesuvius, Etna etc.), Volcanoes of the Aegean Sea. Mt. Ararat, Elburz and Hindukush are also included in this belt.

It is interesting to not that there are several volcanic free zones found along the Alps and the Himalayas. The Rift Valleys of Africa have volcanoes such as Kilimanjaro, Elgon, Birunga and Rungwe etc.

In the region where the boundaries of Persia, Afghanistan, and Baluchistan meet, there are several volcanic cones of large size, and one or two of them emit steam and other gases. This region has also a few extinct volcanoes.

3. The Mid- Atlantic belt:

As the name indicates, this belt includes the volcanoes of the Mid-Atlantic Ridge. The volcanoes associated with the Atlantic Ocean are located either on swells or ridges rising from the sea floor, or on or near the edge of the continent where it slopes abruptly into the deep oceanic basins. However, in each case, the volcanoes are associated with zones of crystal movement.

The volcanoes formed along the Mid-Atlantic Ridge actually represent the splitting zone of the American plate moving towards west and the Eurasian plate moving towards east.

In the splitting zone stated above there is constant upwelling of magmas. Thus, it is a zone of crustal weakness. Volcanoes in this belt are generally of fissure-eruption type. Volcanoes of Lesser Antilles, Azores, St. Helens etc. are included in this belt.

World Distribution of Volcano (in Hindi)

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