A volcano is a geological landform (usually a mountain) where magma (rock of the Earth's interior made molten or liquid by extremely high temperatures along with a reduction in pressure and/or the introduction of water or other volatiles) erupts through the surface of the planet. Although there are numerous volcanoes (some very active) on the solar system's rocky planets and moons, on Earth at least, this phenomenon tends to occur near the boundaries of the continental plates. However, important exceptions exist in hotspot volcanoes.
In the 1960s, scientists developed a revolutionary theory called plate tectonics. Plate tectonics hold that the lithosphere, a layer of rigid material composed of the outer crust and the very top of the mantle, is divided into seven large plates and several smaller plates. These plates drift very slowly over the mantle below, which is lubricated by a soft layer called the asthenosphere. The activity at the boundary between some of these plates is the primary catalyst for magma production.
Magma can also push up under the middle of a lithosphere plate, though this is much less common than magma production around plate boundaries. This interplate volcanic activity is caused by unusually hot mantle material forming in the lower mantle and pushing up into the upper mantle. The mantle material, which forms a plume shape that is from 500 to 1000 km wide, wells up to create a hot spot under a particular point on the earth.
Because of the unusual heat of this mantle material, it melts, forming magma just under the earth's crust. The hot spot itself is stationary; but as a continental plate moves over the spot, the magma will create a string of volcanoes, which die out once they move past the hot spot. The Hawaii volcanoes were created by such a.......
