Resumo de Volcanoes - p.naga prasad

Volcanoes
It is a known fact,as evidenced by themine workers, that
temperature and pressure, increase with depthinside the
earth?s crust. Scientists have estimated that temperatures
would be around 6000 degree centrigrate at the core or
center of our planet. The outer layesrs of rock containing
different types of minerals. There are some
minerals,called the radio-active minerals,such as
radium,uranium,thorium,plutonium etc.,which
cntinuouslyemanate heat. This accumulated heat melts the
rocks around,forming a reservoir of molten rock material
(Magma-when it reaches the earth?s surface,it is called
Lava). While the solid rocks are liquefied ,water vapour
andmanyother gases are released,which,as there is no way
to escape,also occupy the same chamber alongwith the Magma
and exert reat pressure upon it.Hene,magma tries toe scape
to regions where the pressure is comparatively less and
thus,in that process,reaches the surface of the earth heat
and ressure are released,it solidifies again,forming
igneous rocks. Some magma is solidified along the passage
to the eaerath?s surface. This rocess is called
Vulcanicity. A volcano is an opening (vent)on the earth?s
through which rock fragments,lava,cinder,ash,smoke,steam
and other gases suh as sulphur dioxide,ammonium
chloride,hydrogen suplhide and carbondioxide are emitted
during an eruption. There are two types of volcanic
eruptionthe central typeand the fissure type. 1>The
Central type of Eruption:This type of eruptin usually
involves a single ent. The solid and molten rock materials
ejected,accumulate around the vent tforming a hill or a
mountainmore or less conicalin shape. At the apex of these
volcanic cones,are funnel-shaped
depressins,called ?raters?which usually contain ?Crater
Lakes?but fiercely discharge volcanic materials at the time
of an eruption. mount etna insicily.
CotopaxyinEcudor,Vesuvius inItaly,Fujiyama in Japan and the
barren Island in the Andaman islands in India re some of
the typicalexamples of the come shaped volcanic mountains
in the world 2.The Fissure Type of euptin:This type of
eruption involves a series of vents,present along a fault-
line in the earth?s crust,discharging enormous quanitities
of lava,leading to the formatin of lava plains and
plateaus,usually hundreds of square kilometers in area.
The valley of the Snake River, the Columbia Plateau and
the ?Deccan Traps?region of the ppeninsular India may be
cirted as examples,involving this of eruption. Depending
oupon the frequency of eruption,volcanoes are classified as
()active(b)dormant,and (c)extinct. The Volcanoes that
erupt frequency are called the active volcanoes. Mount
Krakatoa in Indonesia,Mount Mauna Loa in the Hawaiian
Islands and the Barren Island east of the Andaman Islands
are some of the good examples for active volcanoes. Those
volcanoes which have erupted in the historic times,but not
recently,are called the dormant (sleeping)volcanoes. Mount
Fuji yama in Japan and Mount Haleakola in Hawaii are some
of the examples. These volcanoes may become active,at
anytime. Those volcanoes which have not recorded any
eruption in the istoric time,are called the extinct
volcanoes.Narcondam,about 150kms north-east f the Barren
Islands in the Indian Ocean,within the territory of India
and Kilimanjaro in Tanzania may be cited as examples.

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