Volcanoes, like the earthquakes is another calamitt that has been plaguing mankind from very early times.
The best known volcano in the world is Mouny Vesuvius near Naples Mt. Vesuvius showed no signs of life for several centuries, suddenly came to life and buried the prosperous cities of Pomperi and Hevenlaneum with their people with a layer of ash and pumice forty kilometre. thick. Since then it has erupted many times, every time destroying neighbouring towns and villages.
How are volcanoes caused? The interior of the earth is a boiling and seething cauldron of molten rocks, steam and gases. This steaming mass and gas accumulate and build up tremendous pressure. They move about the line of weakness in the earth’s crust. They force themselves unto fissures or cracks in the crust and force a vent or hole in the outer layer and come out.
In some cases the molten material from inside the earth quickly wells up and flows out in streams and spreads over the areas around the vent. This lava spreading process continues over long periods until vast areas are covered with layers of lava. In course of time, the lava cools down and forms a vast table land or plateau. The Deccan Plateau, south of the Vindhya Mountains was formed in this way. After long years the lava filled earth forms very fertile soils.
In most cases, the volcanic eruptions are accompanied by rumbling noises and earth tremors. Burning hot rocks, cinders, ash, debris And smoke are blown several kilometres high into the air. Hot lava flows on the sides. Very soon the country side becomes buried under the debris. The sides of the vent rise up forming a cone shaped mound. In the course of years, the cone rises high up until we see a cone shaped mountain towering over the plain. At the top is a wide funnel shaped crater with a gaping hole in the centre. Sometimes the hole becomes plugged with its own lava.
Then the volcano breaks the rock nearby and creates another crater. Thus hundreds of volcanic mountains have been formed in many parts of the world. They can be easily distinguished from the conical shape and smooth sides. When a volcano remains inactive it is said to be dormant. When all activities cease, it is said to be dead or extinct.
Most of the volcanoes are on the edge of the Pacific Ocean. The well known volcanoes of the world are the Katmai in Alaska, Toa near Java, Mount Pelee in the west Indies, Mount Etna in Sicily, Mount Vesuvius near Naples, Fijiyama in Japan, Kilimanjaro in Africa and Chimborago and Cotapaxi in the Andies of South America.