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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