Volcano is the coming out the molten material from the crust of the earth through a vent or pipe which is connected to underlying magma (molten material) chamber. When this molten material or magma is accumulated around the pipe in the form of a mound it is called volcano. The molten material or magma is brought to the surface in the form of volcanic fragments which are commonly known as lava. The temperature of lava ranges between 800° and 13000° Celsius.
Causes of Volcanoes:
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Rocks are found in solid state in the earth’s crust because of overlaying pressure from the rock above it when a crack is developed in rock or earth that is lying above. This causes melting of hot rocks into liquid in small chambers commonly known as magma chambers. Magma (molten material) finds its passage in the zones of weakness, regions of reduced pressure and fissures. Gaseous pressure in some pockets of the earths crust forces magma out. While taking a passage upward it all causes melting of overlying rocks.
Types of Volcanoes on the Basis of Frequency—There are three types of volcanoes on the basis of frequency.
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Dormant Volcano:
Those volcanoes which erupt intermittently are called Dormant Volcano. Fijiyama of Japan, Mt. Visuvius of Italy, Karakota of Indonesia and Barren Island of Andaman & Nicobar are examples of dormant volcanoes.
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Active Volcanoes:
Those volcanoes which erupt frequently are active volcanoes.
Extinct Volcanoes:
Those volcanoes which have not erupted for a very long time but have a record of eruption in the past are extinct volcanoes.
Volcanic Features
Volcanic Vent:
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Volcanic vent is an opening or passage through which lava comes out.
Crater:
Around the vent when extrusion of lava takes place, a saucer shaped depression is formed which is called crater.
Caldera:
Caldera is the enlarged form of crater.
Pyrociastic Material:
Rock and mineral fragments which are blown out along with lava from a volcano are known as pyrociastic materials.
Volcanic Bombs:
Pyrociastic material in solid spindle and spherical shape are known as volcanic bombs.
Spatter Cone: When lave gets accumulated near the vent after being thrown in the air it forms spatter cone.
Volcanic Lapilli:
Particles of lave which varies in size from 4 to 25 mm. are known as volcanic lapilli.
Volcanic Dust or Ash:
Particle in size under 4 mm. is known as volcanic ash or dust.
Tuff—when volcanic ash remains suspended for a long period of time after being thrown up in the air, it is either taken away by wind or falls with rainfall. Finally it is drifted away by running water and gets deposited as sedimentary layer known as tuff.
Types of Volcanoes on the Basis of Style of Eruption
There are two type of volcanoes on the basis of style of eruption.
Types of Fissure Eruption:
When volcanic material or lava comes out from a fissure or group of fissures it freely flows away from the fissures and does not form cones. Deccan traps in India, Columbia Plateau (U.S.A.), Antrum plateau (Ireland) are the examples of such type of volcanic eruption.
Central (Explosive) Type of Eruption:
When lava emanates from central vent or pipe forming a cone. Such style of eruption is known as central (Explosive) type of eruption. Examples of such eruptions are Hawain plateau (U.S.A.)
Active Volcanoes of the World
1. Ojas Del Salade (highest) Andes
2. Guallatiri
3. Cotapaxi
4. Tapungatito
5. Lascor
6. Navado delviz
7. Sangay
8. Popocatepiti
9. Tacana
10. Fuego
11. Purace
12. Klyvchevskaya
13. Soplea
14. Wrangelli
15. Jaju mulco
16. Mt. Cameroom
17. Erebus
18. Rind jani
19. Pico de Te-Teide
20. Semeru
21. Nyira gongo
22. Karyakaskya
23. Irazu
24. Salmat
25. Mount Spurn
26. Mont Etna
27. Agung
28. Kilauae
29. Stromboli
30. Surtesey
31. Ana
Volcanic Zones Zinc Location
1. Circum Specific Belt (Ring of Fire) from Erebus of Antarctic and run northward through Andes and Rockies and come to end to Volcanoes of Island arc (Which include Kamchatka), Japan, Phillipines etc
2. Mid Atlantic Zone along Mid, Atlantic ridge; include Iceland (which is most active volcanic are in this zone) St. Helena, Azores Island etc.
3. Mid-Continental Zone Include Alpine Mountain chains, Mediterranean Sea and Eastern Africa.
4. Intra-Plate Volcanic Zone Hawaiia Volcanic chain, Reunion island Rhine Graben.