Note on Volcanoes

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Volcanoes Process Magma is formed when the lower crust or upper mantle melts as a result of tectonic activity. This magma (and its various components) is discharged through a vent or opening referred to as a volcano. Thus in basic terms, volcanic eruptions are caused by the rise of magma from the earth's interior. According to Manroe, Wicander and Hazlett, in comparison to the surrounding solid rock, magma tends to be less dense (107). In the authors' words, "the greater the difference in density between melt and country rock, the faster magma rises" (Manroe, Wicander and Hazlett, 107). It is however important to note that as magma gets close to the earth's surface, it assumes a neutral buoyancy position (Manroe, Wicander and Hazlett, 107). This is brought about by a drop in the contrast of density between melt and the surrounding solid rock. It should be noted that if sufficiently shallow, magma in the aforementioned buoyancy position could still erupt. This according to Manroe, Wicander and Hazlett could happen as a result of the buildup of what is referred to as volatiles (107). It should also be noted that as it approaches the surface, magma changes in terms of volatile composition. As Manroe, Wicander and Hazlett point out, the assimilation of ground water effectively increases the melt's dissolved H2O content (107). According to the authors, it is the expansion of dissolved water into steam that in some instances triggers explosive volcanic eruptions. A volcanic
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