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Volcanoes & its Types

Volcanoes

  • A sudden & abrupt explosion in earth crust through which Magma, gases, dust, smoke & solid material burst out
  • Volcanic activity is connected with crustal disturbances, closely related with regions that have been intensely folded or faulted
  • Magma while thrusting its way upto the surface may cool & solidify within crust as Plutonic rocks resulting in intrusive landforms
  • Magmas that reach the surface & solidify, form extrusive landforms

parts volcano

Sills & Dikes (Common intrusive landforms)

  • When an intrusion of molten magma is made horizontally along the bedding planes of sedimentary rocks, the resultant intrusion is called a Sill.
  • Similar intrusion when injected vertically as narrow walls of igneous rocks within the sedimentary layers are termed as Dikes.

Igneous intrusions on a larger scale are various types of Liths viz. Laccoliths, Lopoliths, Phacoliths & Batholiths

Laccoliths, Lopoliths, Phacoliths & Batholiths

Laccoliths An igneous mound with a dome shaped upper surface & a level base, fed by a pipe like conduit from below
Lopolith An igneous intrusion with a saucer shape
Phacolith A lens shaped mass of igneous rock occupying the crest of an anticline or the bottom of a syncline & being fed by a conduit from beneath
Batholith A large emplacement of igneous intrusive rock, mainly granite, that forms from cooled magma deep in the Earth’s crust

Extrusive Landforms

  • Lava or molten magma ejects at a very high pressure through a pipe known as Volcano’s neck or vent
  • Top portion of volcano is known as crater and a crater lake is formed when rain water gets accumulated in
  • Some volcanos may have greatly enlarged depressions like cauldron known as Calderas
  • Volcanic dust or ash (finer particles) that emerges out of volcano travels round the world & falls as black snow, which can bury house & people.
  • The coarser fragmental rocks are collectively called as Pyroclasts which include cinders, pumice & volcanic bombs.


Types of Volcanoes

Active Volcano

  • Keeps on ejecting volcanic material at frequent intervals
  • Ex – Etna (Italy), Stromboli (Sicilylargest island in the Mediterranean Sea, near Italy)
  • Mt Stromboli Lighthouse of the Mediterranean

Types of Volcanoes

Dormant Volcano

  • One in which eruption has not occurred for a long time but can occur any time in future
  • Barren Island (Andaman), Versuris (Italy)

 

Extinct Volcano

  • No eruption has occurred in historic times & possibility of future eruption is also remote
  • Mt. Popa (Myanmar). But we can never be thoroughly sure about them.
  • Vesuvius (Bay of Naples near Italy) & Mt. Krakatau (Sunda straits b/w Java & Sumatra) were thought to be extinct & yet both erupted violently

 


Distribution of Volcanoes in the world

  • There are mainly three volcanic belts, besides many volcanoes which are outside these belts
  • Circum-Pacific belt    →  known as Ring of fire & houses around 2/3rd of world’s Volcanoes
  • Mid-Continental belt   This belt has various volcanoes of the Alpine mountain chain, Mediterranean Sea (Stromboli, Vesuvius, Etna etc.)
  • Mid-Atlantic belt        →  This belt includes the volcanoes of the Mid-Atlantic Ridge

Distribution of Volcanoes in the world


Geysers

  • A spring characterized by intermittent discharge of water ejected turbulently and accompanied by steam
  • The phenomenon is associated with a volcanic region in which the water below is being heated beyond its boiling point
  • Is often triggered off by the gases seeping out of the heated rocks.
  • Examples include Iceland; New Zealand & Yellowstone park of USA
  • The world’s best known geyser is perhaps old faithful in Yellowstone National park, Wyoming

Geysers and Hot spring


Hot springs

  • A spring that is produced by the emergence of geothermal heated groundwater from the Earth crust
  • Is more common than geysers
  • The water rises to surface without any explosion
  • Such springs contain dissolved minerals which may be of medical value
  • Examples Include Iceland, Japan & Hawaii

 

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