Volcanoes
Introduction
The volcano is an important natural hazard.
It causes great damage to life and property.
The volcano is a vent or opening, through which heated materials consisting of gases, hot water, lava, and fragments of rocks are ejected from the interior of the earth.
The passage of the earth’s crust through which magma and other volcanic materials are ejected is called the vent.
The funnel-shaped hollow at the top of the cone of a volcano is called a crater.
The scientific study of volcanoes is called volcanology.
Materials that come when volcanoes take place are called pyroclastic materials.
Causes for volcanoes
The temperature inside the earth increases with increasing depth (1° C per 32m)
Formation of magma because of increased temperature and pressure reduction.
Gases and water vapor are formed due to underground water heating.
Movement and breaking of major and minor plates of the earth.
Ascent of magma forced by excess pressure
Types of volcanoes
1. Active volcanoes
Volcanoes that constantly eject solid, liquid and gaseous materials are called active volcanoes.
Example:
Mt Etna and Stromboli of Italy.
St Helens of USA
Mauna loa and Mauna Kea of the Hawaiian islands
Pinatubo of Philippines , Cotopaxi and Chimborazo of Ecuador
Izalco of El Salvador
Facts to be remembered
Stromboli is known as a lighthouse of the Mediterranean
Izalco is called the lighthouse of central America
2. Dormant volcanoes
These volcanoes become quiet after the eruption but erupt after a long period of time.
Example:
Mt Fujiyama of Japan
Mt Krakatau of Indonesia.
Mt Vesuvius of Italy
Facts
Mt Vesuvius, Mt Krakatau, and Mt. Pelean Volcanoes are called super Volcanoes.
3. Extinct volcanoes
The volcanoes have not been active for a considerable period of time.
These are called dead volcanoes.
Example:
Narcondum ( Andaman and Nicobar islands of India).
Barren islands of Andaman and Nicobar islands are important volcanoes in our country. It is an Active volcano.
Volcanic materials
The three types of materials ejected from the volcanoes.
A. Liquid materials
Lava is the most important liquid material ejected by volcanoes.
There are two types of lava.
Acid lava: It has a high percentage of Silica.
Basic lava: It has a low percentage of Silica.
Magma: the molten material found below the earth’s surface
Lava: when molten material reaches the surface of the earth
B. Solid materials
Volcanic bombs, dust, pumice, scoria, volcanic ash, cinder and rock fragments.
C. Gases
Sulphur, hydrogen, and carbon dioxide.
Distribution of volcanoes
1. The Circum-Pacific belt
Also called as pacific ring of fire
It is found in the eastern part of New Zealand, New Guinea, Philippines, Japan, the western part of Alaska, the USA, Hawaiian islands,
This belt experiences a greater number of volcanoes.
2. Midcontinental belt
Found in Alpines, the Mediterranean region, Europe, North Africa Etc.
3. Mid – Atlantic belt
This belt is found in the Mid-Atlantic Ridge, Iceland, etc
Effects of volcanoes
It can cause damage to life and property.
Volcanoes cause damage to agricultural fields, industries, dwelling roads, railways, airports, dams, reservoirs, etc.
It causes diversion of river course and flooding of water.
It can cause air pollution.
It can form rocks and minerals.
Volcanoes in Indian Regions
Barren Islands
SI NO |
Volcanoes in India |
Regions |
1. |
Barren Islands- |
Andaman and Nicobar |
2. |
Deccan Traps |
Maharashtra |
3. |
Narcodam |
Andaman and Nicobar |
4. |
Bhar tang |
Andaman and Nicobar |
5. |
Tosh am Hills |
Haryana |
6. |
Dhoni Hills |
Borders of Haryana and Rajasthan |
7. |
Dhinodhar Hills |
Gujrat |