Volcanoes

A volcano is a narrow opening in the earth's crust through which magma and other materials erupt from the interior of the earth. The temperature at a depth at a depth of a few kilometers would be above the melting point of rocks but high pressure makes them remain in the solid state. When the pressure is released a deep joint, the material changes to a liquid state and erupts to the surface through the pipe. Volcanic eruption may last for a few days at a time because the materials in the deeper layers become solid once again.
Causes of volcanoes
Two causes of volcanic eruptions are as follows:
A.    The temperature at depth of a few kilometers would be above the melting point of rocks but the high pressure makes them remain in the solid state. When the pressure is released a deep joint the material changes to a liquid state and erupts to the surface through the pipe. This is called volcano.
B.     By the different causes there will be movement in the interior part of the earth and causes earthquake. Because of the earthquake on the surface of the there will be rifts. From the first lava, ashes, fire come out to the surface of the earth. This is called volcanic eruption.
Types of volcanoes
Volcanoes are classified into three major types on the basis of the frequency of their eruption. The three types are as follows:
i.                    Active Volcanoes
ii.                 Dormant Volcanoes
iii.               Extinct Volcanoes
(i)                Active Volcanoes:
Active Volcanoes are those, which have erupted in the recent historic periods. There are about 500 active volcanoes in the world. Mt. Vesuvius, Mt Etna in Italy are examples of active volcanoes.
(ii)             Dormant Volcanoes
Dormant Volcanoes are those, which have erupted in the past but, have remained inactive for fairly long periods. These are "sleeping" volcanoes, which may become active once again. These are located in the belts of young Fold Mountains where the crust is unstable. Some volcanoes in the West Indies, Philippines and Japan considered as dormant volcanoes.
(iii)           Extinct Volcanoes
Extinct Volcanoes are those which were active in the remote geological periods. These are not likely to be active once again. Mt. Kilimanjaro in Africa is an example of Extinct Volcano.
Distribution of Volcanoes
There are evidences of volcanoes activity during the long period of geological history of the earth. There are thousands of extinct volcanoes both on the continents and the ocean floors. At present there are about 500 active volcanoes on the surface of the earth. These are found mostly in the unstable portions of the earth's crust. These are mainly belts of young Fold Mountains.
(i)                The Circum-pacific belt
This belt contains nearly 80% of the total number of active volcanoes. This is called the "Pacific Ring of Fire" because the volcanoes occur along the margins of the Pacific Ocean. This belt includes the Andes Mountains of South America, and the Rockies of North America. It is estimated that there are 40 active volcanoes in the Andes, 35 in Japan, 100 in the Philippines and 70 in Indonesia.
(ii)             Mid-world Mountain belt
This belt of young Fold Mountains has fewer active volcanoes than the Circum-Pacific belt. This belt coincides with the Alpine-Himalayan Mountains which extend through Europe and Asia. This belt bends southwards through the Andaman and Nicobar Islands and merges with the Circum-Pacific belt in Indonesia. Mt. Vesuvius, Mt. Stromboli and Mt. Etna in Italy are examples of volcanoes in this belt. There are no active volcanoes in the Himalayan ranges.
(iii)           Rift Valley Mountain belt
Several volcanic areas are found in the eastern rift areas of Africa continent. Kenya and Kilimanjaro are the major volcanoes of this area. The volcanoes of the area are almost dead.
Influences of Volcanoes in the human life:
Influences of volcanoes are mainly divided into three types.
i.                    Destructive influences

ii.                 Useful in flounces.
iii.               Influences on land forms.
i.                    Destructive influences:-
a.      Volcano causes a loss of human life as well as other creatures.
b.      Ashes, lava etc. effected from the volcano cover the residential area as well as fertile land.
c.      The fore of the volcano causes fire on the residential areas:
ii.                 Useful influences:-
a.      Many metals are ejected out of volcanoes.
b.      Lava which is ejected out of volcanoes makes the soil fertile.
c.      From the heat of the volcano we can generate electricity.
iii.               Influences of land forms:-
a.      Volcanic mountains are formed. For example Fuji mountain of Japan.

b.      Lava ejected out of volcano spreads widely and formed a new land.
c.      Lava piles up around the crater of the volcano and new mountain is formed.
d.      Volcanic lakes are formed.