Causes of volcanoes: Various factors are responsible for occurrence of volcanic eruptions.
Following are the major factors among them:
1. Unbalance (a word used about a person slightly crazy).
2. Evolution of gases.
3. Increase in temperature of the crust.
4. Decrease in pressure.
5. Plate tectonics.
Classification of Volcanoes:
Volcanoes have been mainly classified on two bases:
1. On the basis of period of eruption.
2. On the basis of nature of eruption.
1. Types of volcanoes on the basis of their period of eruption: On the basis of their period of eruption,
volcanoes have been further classified into the following types:
(a) Active or Waking Volcano: Those volcanoes which continuously erupt are known as active volcanoes.
For example: Etna and Stromboli.
(b) Dormant Volcanoes: Those volcanoes which remain inactive for some time and erupt again are known as dormant volcanoes.
For example: Mount Vesuvius.
(c) Extinct or Dead Volcanoes: Those volcanoes which have not erupted since a long time and in which water, etc. has filled in crater are known as extinct volcanoes.
For example: Mount Popa, Koh-i-Sultan, etc.
2. Types of volcanoes on the basis of their nature of eruption:
- Volcanoes with central eruption
- Volcanoes with fissure eruption
Volcanoes with central eruption: Those volcanoes which erupt from a single bore and a single vent are known as volcanoes with central eruption.
Such volcanoes have been further classified into the following parts:
1. Hawaiian types of volcanoes.
2. Stromboli – an types of volcanoes.
3. Volcanian types of volcanoes.
4. Pelean types of volcanoes.
1. Hawaiian Type of Volcanoes: Explosive activity is less in this type of volcano and it erupts in a silent manner. The main reason for this is thinness of lava and lack of fierceness in gases. Examples of this type of volcanic eruptions are seen mainly in Hawaiian Islands, therefore they are known as Hawaiian type of volcanoes.
2. Strombian Type of Volcanoes: In this type of eruption, lava comes out in a relatively fierce manner, it is thick and sometimes the eruption is explosive. This type of eruption occurs in Stromboli volcano. On its name, volcanoes with this type of eruptions are known as strombolian type of volcanoes.
3. Volcanian Type of Volcanoes: In this type of volcano, volcanic substances erupt with terrific explosion and excessive fierceness and after the explosion, gases mixed with ash and dust emerge up to a great height in the form of massive black clouds and they are visible shaped like a cauliflower. Naming of this type of volcanoes has been done on the basis of Volcanian volcano of Lipari Group of Islands.
4. Pelean Type of Volcanoes: In this volcano, eruption is most fierce and violent and this is the most destructive type of volcano. Volcanoes which erupt just like the explosive eruption taking place in Pelee volcano situated in Martinique Islands in the western island group are known as Pelean type of volcanoes.
Volcanoes with Fissure Eruption: In such volcano, lava erupts from fissure in a silent manner without any explosion. Lava is usually thin and as a result of this, lava plateau is formed. Colombian Plateau and Deccan Plateau of India are lava plateaus formed by fissure eruption.
