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ClearIAS » Disaster Management Notes » Volcanoes: Everything You Need To Know

Volcanoes: Everything You Need To Know

Last updated on January 16, 2017 by Clear IAS Team

A volcano is an opening in the earth’s crust through which gases, molten rocks materials (lava), ash, steam etc. are emitted outward in the course of an eruption. Such vents or openings occur in those parts of the earth’s crust where the rock strata are relatively weak. Volcanic activity is an example of endogenic process. Depending upon the explosive nature of the volcano, different land forms can be formed such as a plateau (if the volcano is not explosive) or a mountain (if the volcano is explosive in nature).

Magma vs Lava: The difference

  • Magma is the term used to denote the molten rocks and related materials seen inside earth. A weaker zone of the mantle called asthenosphere, usually is the source of magma.
  • Once this magma came out to the earth surface through the vent of a volcano, it is called as the Lava. Therefore, Lava is nothing but the magma on earth surface.
  • The process by which solid, liquid and gaseous material escape from the earth’s interior to the surface of the earth is called as Volcanism.

Types of Volcanoes

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.

Types of Volcanoes

Shield Volcanoes

  • How to identify: They are not very steep but are far and wider. They extend to great height as well as distance.
  • They are the largest of all volcanoes in the world as the lava flows to a far distance. The Hawaiian volcanoes are the most famous examples.
  • Shield volcanoes have low slopes and consist almost entirely of frozen lavas.
  • If you were to fly over top of a shield volcano, it would resemble a warrior’s shield, hence the name.
  • These volcanoes are mostly made up of basalt (less viscous), a type of lava that is very fluid when erupted. For this reason, these volcanoes are not steep.
  • They are of low explosive in general, but if somehow water gets into the vent they may turn explosive.
  • The upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into cinder cone

Cinder Cone Volcanoes:

  • Cinders are extrusive igneous rocks. A more modern name for cinder is Scoria.
  • Small volcanoes.
  • These volcanoes consist almost entirely of loose, grainy cinders and almost no lava.
  • They have very steep sides and usually have a small crater on top.

Composite Volcanoes:

  • Shape: Cone shaped with moderately steep sides and sometimes have small craters in their summits.
  • Volcanologists call these “strato-” or composite volcanoes because they consist of layers of solid lava flows mixed with layers of sand- or gravel-like volcanic rock called cinders or volcanic ash.
  • They are characterized by the eruption of a cooler and more viscous lavas than basalt.
  • These volcanoes often result in explosive eruptions.
  • Along with lava, large quantities of pyroclastic materials and ashes find their way to the ground.
  • This material accumulates in the vicinity of the vent openings and leading to the formation of layers, and this makes the mount appears as composite volcanoes.

Caldera:

  • These are the most explosive of the earth’s volcanoes.
  • They are usually so explosive that when they erupt they tend to collapse on themselves rather than building any tall structure. The collapsed depressions are called calderas.
  • Their explosiveness indicates that its magma chamber is large and in close vicinity.
  • A caldera differs from a crater in such a way that a caldera is a huge depression caused by a collapse after a large-scale eruption, whereas a crater is a small, steep side, volcanic depression bored out by an eruptive plume.

Flood Basalt Provinces

  • These volcanoes outpour highly fluid lava that flows for long distances.
  • The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province.

Mid-Ocean Ridge Volcanoes

  • These volcanoes occur in the oceanic areas.
  • There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.
  • The central portion of this ridge experiences frequent eruptions.

Volcanoes can also be classified based on the frequency of eruption, mode of eruption and characteristic of lava.

Classification of Volcanoes

Volcanic Landforms:

  • The lava that is released during volcanic eruptions on cooling develops into igneous rocks.
  • The cooling may take place either on reaching the surface or from the inside itself.
  • Depending on the location of the cooling of lava, igneous rocks are classified as:

Volcanic Igneous rocks (Extrusive igneous rocks):

Cooling of the rock occurs at the surface of the earth.  E.g. Basalt, Andesite etc.

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Plutonic Igneous rocks (Intrusive igneous rocks):

Cooling takes place in the crust and not over the surface. E.g. Granite, Gabbro, Diorite etc. Intrusive igneous rocks are classed into the following types according to their forms.

  1. Batholiths: A large body of magmatic material that cools in the deeper depth in the form of a large dome. These are granitic bodies. They sometimes appear on the earth surface when the denudation processes remove the overlying materials.
  2. Laccoliths: Large dome shaped intrusive bodies with a level base and pipe-like conduit from below. Resembles a composite volcano structure, but beneath the earth. (Eg: Karnataka Plateau)
  3. Lapoliths: They are saucer shaped, concave to the sky.
  4. Phacoliths: Wavy materials which have a definite conduit to source beneath.
  5. Sheets/ sills: They are the near horizontal bodies of intrusive igneous rocks. Thinner ones are called as sheets and while thick horizontal deposits are called sills.
  6. Dykes: When the lava comes out through cracks and fissures, they solidify almost perpendicular to the ground to form wall like structures called dykes. (Eg: Deccan traps in Maharastra region).

Intrusive igneous rocks

Distribution of Volcanoes:

Most of the volcanoes in the world are found in three well defined belts:

  1. The Circum-Pacific Belt (The Pacific Ring of Fire).
  2. The Mid-World Mountain Belt.
  3. The African Rift Valley Belt.

Distribution of Volcanoes

Volcanic Activity – Points to note down:

  • Volcanoes are closely related to the regions of intense folding and faulting.
  • They occur along coastal mountain ranges, on islands and in the mid oceans.
  • Interior parts of the continent are generally free from their activity.
  • Most of the active volcanoes are found in the pacific region which is thus called as the Pacific Ring of Fire.

Next article in the series: Earthquakes: Everything You Need To Know.

Article by: Jijo Sudarshan

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Reader Interactions

Comments

  1. YAKSH KUMAR says

    February 14, 2016 at 6:53 am

    Very precise and lucid explanation sir. It’s really helpful. Please keep writing such articles as frequently as possible.

    Reply
  2. Vijaykarthik says

    February 17, 2016 at 1:49 pm

    Sir, this site is very helpful to learn the basics and tough concepts due to its lucid nature.However , please ensure that the concepts are updated regularly to boost students knowledge constantly. Thanks for your preparation.

    Reply
  3. poonam says

    February 25, 2016 at 10:35 am

    Sir…complete information about volcanoes. Pls make videos on earthquakes,tsunami etc…it will great help

    Reply
  4. srikar says

    April 25, 2016 at 2:37 pm

    Thankyou very much sir……….it is informative and interesting…….great work .

    Reply
  5. Batunso says

    May 26, 2016 at 9:32 am

    Thank you sir. Very good explanation in simple language. Kee it going sir.

    Reply
  6. Akanksha says

    January 17, 2017 at 9:18 pm

    Thanks sir very useful information. .feeling confident now as getting such valuable informations. ….Thanks once again and please continue this. .. …….

    Reply
  7. Lekha says

    February 7, 2017 at 11:35 am

    Thanku so much for providing such a precise knowledgeable notes based on NCERT text book …I had a lot of doubts while I’m redg the text , but all those doubts are cleared now …Thank u sir

    Reply
  8. Varsha says

    June 6, 2017 at 10:50 pm

    Thanks sir
    Its really nice …

    Reply
  9. phg says

    September 25, 2017 at 8:55 am

    collected information is very good sir

    Reply
  10. Gurpreet kaur says

    September 27, 2017 at 2:38 pm

    Quite confusing if we see the diagram and then description both are condtradicting …..u have explained about fissure and heading is of sheild….plz provide the correct information…either the diagram is wrong or its description plz correct it..ty

    Reply
  11. swathi says

    May 24, 2018 at 8:06 am

    thanks a lot sir!..it’s really helpful!..great effort..

    Reply
  12. ayesha says

    July 29, 2018 at 1:49 pm

    Tnx a lot sir…. Helpful in mastering tough concepts

    Reply
  13. Ntim Samuel says

    November 3, 2019 at 3:53 am

    Thanks so much for such useful information
    It is really helpful especially for my assignment

    Reply
  14. Shedreonna says

    December 10, 2019 at 10:14 pm

    how do the volcanoes erupt in Hawaii

    Reply
  15. Madolina Baruah says

    April 15, 2020 at 2:03 am

    Thanx a lot sir for your guidance.its really so much helpful.when i first started actually i have no any idea what to read,bt through your valuable guidance now understand the basic.

    Reply
    • ClearIAS.com says

      April 15, 2020 at 5:55 am

      Great to know that. All the best!

  16. donna blah says

    January 14, 2021 at 10:22 pm

    my teacher assigned me to this website, and I’m more than confused

    Reply

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