In general, volcanoes are created when magma, or molten rock, rises through the earth.s crust to the surface. The magma is usually originates from under the earth's crust, located in the mantle layer of the earth. The magma rises, melting and pushing itself up through the earth's surface. The main factor that causes the magma to rise is the properties of tectonic plates which create weak areas in the earth's crust where magma can flow through.The main reason magma is able to rise to the surface to create volcanoes is due to tectonic plates. Volcanoes are most common at areas where tectonic plates meet. At those areas, the tectonic plates are moving slowly, diverging or converging, allowing volcanoes to form in different ways.Divergent: When tectonic plates are diverging, this leaves an opening in the earth.s crust which allows the liquid magma to flow up creating volcanoes. This normally happens in the ocean, like the Mid-Atlantic Ridge, which creates underwater volcanoes and islands.
Convergent: When tectonic plates are converging, normally one plate goes under the other. This creates a lot of friction and when the lower plate goes low enough, it begins to melt, creating magma. This magma flows upward through the upper plate melting the crust and creating a magma chamber. If the magma is restricted from flowing onto the surface, the pressure builds up in the chamber and eventually the magma is ejected through the crust as a volcanic eruption.
Mount Pelée is the result of a subducting convergence of the Atlantic and Caribbean plates. In the case of this volcano, the Atlantic plate subducts beneath the Caribbean.
(Upper Right Picture: Tectonic Plate Map)
