The term Volcano is derived from the name Vulcan, The Roman God, applied to Mt. Etna in Sicily and to some of the volcanoes of the Lipai Islands north of Sicily. The term Volcanism is used to embrace all aspects of volcanic activity, the name volcano is generally
Applied to the surf ace form which develops around a central vent which may be an orifice or a fissure through which hot incandescent magmatic materials are continuously or intermittently ejected. It is often symmetrical in shape. A volcanic mountain differs structurally and genetically from the majority of the world’s mountains. As the solid materials Accumulate around the vent of conduit they build up a cone which increases in size until a Huge volcanic mountain is formed. A cone so constructed is called a volcano.
Volcanoes may vary in size from small conical hills to some of the loftiest Mountains on the earth’s surface. Some of the highest peaks like Cotapaxi in Equador has The distinction of being the highest volcano 6380 mtrs. High. Mount Kilimanjaro, Mount Fiji And Mount Mayon are examples of such perfect conical shape. The Hawaiian Islands are Volcanoes that reach a height of more than 4200 mtrs. Above sea-level and they are built on The ocean floor of the pacific where the depth is more than 4200 to 5400 mtrs. Not all Volcanoes are active at present and some of them have become extinct like the Mt.Shasta, Mt. Rainier, Mt. Hood, MT. Baker in the cascade ranges of western U. S. Mt. Etna in Sicily is A high mountain built as a volcano that is still active. Every well-developed volcanic cone Has near its top volcano crater a kind of funnel-shaped depression out of which volcanic Material are thrown out, up during explosive eruptions. In some volcanoes lavas emerge Through the crater, in others they break through the sides of the cone or emerge from the Fissures beyond the base. It should be noted that the magma is not merely molten rock but It differs essentially from the latter in being charged with gases and volcanic constituents just As aerated waters differ from ordinary water. While the magma is confined under high Pressure its gaseous constituents remain dissolved, but as it comes on to the surf ace the Overhead pressure is reduced and the gases begin to get liberated either freely or explosively According to local circumstances. The molten matter erupted at the surface is thus relatively Impoverished in gases and volatiles and then is called lava to distinguish it from the original Magma. In a volcanic eruption not only the eruption of hot gases and molten lavas, but also Vast quantities of fragment materials often produced by the explosion of rapidly liberated Gases. Such materials are collectively known as pyroclastic and they contain from the finest
Particles to masses of scoria and volcanic bombs of considerable size. The popular belief that Volcanoes are burning mountains arises from the fact that the volcanic pyroclastic materials Including hot gas often may be luminous because they are incandescent.