Volcanoes evoke more interest in humans than anything else in nature. Volcanoes have been the cause of superstitious worships for several groups of people throughout history. Volcanoes have both the power to create as well as to destroy. According to Gordon MacDonald, in his book Volcanoes, defined a volcano as, "a place or opening which molten rock or gas, and generally both, issue from the earth's interior onto its surface, and the hill or mountain built up around the opening by accumulation of the rock materials" (22). Volcanoes are not scattered erratically about the earth but occur in clusters usually just a few hundred miles from the ocean. There are so many volcanoes along land that borders the Pacific Ocean that the area is labeled the "Ring of Fire." The "Ring of Fire" is an arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. .
Magma, rising from lower reaches, gathers in a reservoir, in a weak portion of the overlying rock called the magma chamber. Eventually, but not always, the magma erupts onto the surface. Strong earthquakes accompany rising magma, and the volcanic cone may swell in appearance, just before an eruption. Scientists often monitor the changing shape of a volcano, especially prior to an eruption. The different reasons why a volcano forms are via plumes or hot spots in the lithosphere or as a result of subduction of the nearby lithosphere.
Volcanoes form when hot material from below rises and leaks into the crust. This hot material, called magma, comes either from a melt of subducted crustal material, and which is light and buoyant after melting, or it may come from deeper in the interior of the earth and is light and buoyant because it is very hot. .
Hot magma, rising from lower reaches of the Earth, eventually, but not always, erupts onto the surface in the form of lava.