VOLCANOS

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Volcanic activity in Semeru in Indonesia

ABOUT

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.

TYPES

Shield Volcanoes

• 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
• 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:

  • Cindersare 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.