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Volcanoes

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Causes of volcanic eruptions

The main causes of volcanic eruptions are the following:
(i) Heat and pressure inside the earth
(ii) Plate tectonics
(iii) Magma chamber

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Structure of Volcano

The very hot material that the volcano pours out creates, both inside the earth and on the surface, structures typical of a particular type of eruption. The eruption may take place quietly or violently. 
Vent: The lava flows out through an opening in the earth's crust is called Vent.
Volcanic cone: The erupted fluid material being hot collects around the vent and begins to cool gradually and solidifies. The accumulation of material around the vent gives to the volcano its typical cone-like shape known as the volcanic cone.

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Types of volcanoes

Volcanoes are classified in several ways. On the basis of frequency of their eruptions, volcanoes are classified into three main types:
(i) Active
(ii) Dormant
(iii) Extinct.

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Important volcanic zone of the world

The volcanoes occur near earthquake belts around the young-fold mountains. The Circum Pacific Belt is also called the Pacific Ring of Fire because over 80% of the total number of active volcanoes are concentrated in this region. The famous active volcanoes - Mt. Vesuvius, Mt. Etna and Mt. Stromboli - are located in the Midworld Mountain Belt.

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Products of a volcano

A volcano erupts a number of products like steam, gases, molten rock, dust, ashes and other liquid and solid matter. The molten rock material inside the earth is known as magma.  When it reaches the surface of the earth, it is known as lava. Steam and other gases such as hydrogen, carbon dioxide, steam come out from a volcano. Solid fragments are rock pieces known as pyroclasts whereas the finest particles are called dust. Small stones size particles are called lapilli.

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Effects of volcanoes

Effects can be constructive as well as destructive. 
1. Loss of life and property.
2. Sometimes, tsunamis get generated due to volcanic eruptions occurring below ocean floors.
3. Dust, smoke, ash, gases, water vapour, etc., remain in the atmosphere for a long time. This may create imbalance in the environment.
4. Land may become fertile due to volcanic ash.
5. Many minerals are found near the earth's surface because of lava.
6. New land is formed due to volcanic eruption or at times, an island may even disappear.
7. Lakes are formed at the mouth of the craters of dead volcanoes when water water accumulates in them.

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Extrusive landforms

i) Cone and crater
ii) Composite cones
iii) Caldera 
iv) Lava shields
v) Lava plateau

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Constructive effects of volcanoes

The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil. This creates very fertile soil which is good for agriculture. The high level of heat and activity inside the Earth, close to a volcano, can provide opportunities for generating geothermal energy.

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Destructive effects of volcanoes

Volcanoes are considered as great environmental hazards Volcanoes spew gases and dust in the atmosphere and cause great loss of life and damage to property as well as to the natural environment. Lava flows and lahars can destroy settlements and clear areas of woodland or agriculture.

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Volcano

When hot liquid and gaseous materials are thrown out from the mantel of the earth into the surface, its called a volcano. During this process ash, water vapour,various types of poisonous and inflammable gases, hot molten magma are thrown out. The hot molten magma are called lava. Volcano consists of different parts like vent, magma chamber, volcanic cone, crater etc.

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Extinct volcano

Those volcanoes which have not erupted in the past since long and are not likely to erupt in the future are called extinct volcanoes. For example, Mt. Kilimanjaro volcano in Tanzania.

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Active volcano

If the volcanic eruptions are regular even in the present times, then such volcanoes are called active volcanoes. For example, Mt. Fujiyama in Japan, Mt. Stromboli in Mediterranean Sea.

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Dormant volcano

When a volcano has not erupted since long, but may become actively suddenly it is called dormant volcano. For example, Mt. Vesuvius in Italy, Mt. Katmai in Alaska, Barren Island, India.
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Volcano- Introduction and Major Types
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