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 up to the surface may cool & solidify within crust as Plutonic rocks resulting in intrusive landforms.
Magmas that reach the surface & solidify, form extrusive 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	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

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.

Keeps on ejecting volcanic material at frequent intervals
Ex – Etna (Italy), Stromboli (Sicily-largest Island in the Mediterranean Sea, near Italy)
Mt Stromboli [arr] Lighthouse of the Mediterranean

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

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

- There are mainly three volcanic belts, besides many volcanoes which are outside these belts.
- Circum-Pacific belt [arr] known as Ring of fire & houses around 2/3^rd of world’s Volcanoes.

Mid-Continental belt [arr] This belt has various volcanoes of the Alpine Mountain chain, Mediterranean Sea (Stromboli, Vesuvius, Etna etc.)
Mid-Atlantic belt [arr] This belt includes the volcanoes of the Mid-Atlantic Ridge

- 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

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