文章:
What causes a volcano to erupt and how do scientists predict eruptions?
Attila Kilinc, head of the geology department at the University of Cincinnati, offers this answer. Most recently, Professor Kilinc has been studying volcanoes in Hawaii and Montserrat.
When a part of the earths upper mantle or lower crust melts, magma forms. A volcano is essentially an opening or a vent through which this magma and the dissolved gases it contains are discharged. Although there are several factors triggering a volcanic eruption, three predominate: the buoyancy of the magma, the pressure from the exsolved gases in the magma and the injection of a new batch of magma into an already filled magma chamber. What follows is a brief description of these processes.
As rock inside the earth melts, its mass remains the same while its volume increases--producing a melt that is less dense than the surrounding rock. This lighter magma then rises toward the surface by virtue of its buoyancy. If the density of the magma between the zone of its generation and the surface is less than that of the surrounding and overlying rocks, the magma reaches the surface and erupts.
Magmas of so-called andesitic and rhyolitic compositions also contain dissolved volatiles such as water, sulfur dioxide and carbon dioxide. Experiments have shown that the amount of a dissolved gas in magma at atmospheric pressure is zero, but rises with increasing pressure.
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2016-02-26
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