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Earth - Volcanoes
Earth - Volcanoes
The mountains which throw up fire, smoke ad cinder are called volcanoes. When volcanoes erupt, the magma melted rock reservoir in the layers of the earth’s interior forces itself out through the crust to the surface of the earth. The liquid substance that is forced out as a result of volcanic eruption is called lava. The lava is a mixture of hot volcanic cinder, pieces of rocks and steam. The number of active volcanoes on the earth is estimated from about 500 to over 800. Most of the volcanoes are funnel or cone shaped. Their mouth is called crater. The crater is connected to a pipe-like opening though out. By the action of gases and steam accompanying the magma, the rocks at the top and slopes are blown up to form a hole. Mt Fujiyama, in Japan, is an example of such a volcanic mountain. Some volcanoes have dome like tops. They are called shield volcanoes. Mauna Loa in Hawaii Island is an example of Shield Mountain.
On the basis of the amount of their activity, the volcanoes are classified as 1. Active 2. Dormant and 3. Extinct. An active volcano is always erupting. Hawaii Island’s Mauna Loa and Sicily’s Mt. Etna are examples of active volcanoes. A dormant volcano is temporarily inactive. Examples of such volcanoes are Mt. Fujiyama in Japan and Mt. Vesuvius in Italy. An extinct volcano remains completely inactive for in hundreds or thousand of years. Mt. Kilimanjaro in Africa and Mt. Aconcagua in South America are example of extinct volcanoes. The world’s highest extinct volcano is in Argentina which is about 6960 meter high.
Volcanic eruptions sometimes cause large scale destruction. Pompeii and Herculaneum were buried under eruption from Visurius. Volcanic eruption in 1883 blew off two-third of Krakatoa island of Indonesia. It was the greatest explosion during the last 3000 years. The magnitude of this explosion was equal to that of 1500 megaton of TNT and it was heard as far as 500 kilometers. Besides this, the explosion resulted in tidal waves in all the seas and oceans across the globe.
A volcano is a vent or fissure in the earths crust through which hot solids, gases, smoke and liquids emerge out violently. A volcano also refers to the mountain that forms around the hill.