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Before talking
about predicting eruptions, we need to look at why they occur.
How do volcanoes form?
Deep inside Earth, between the molten iron core and the
thin crust at the surface, there is the mantle, a large layer of rock that is largely solid, but flows like plastic. When, for various reasons, rock from the mantle melts, it sometimes moves to the Earth?s surface through weak spots in the crust, releasing heat, gasses, and rock--a volcanic eruption. But why does this solid rock melt and come to the surface?
From Magma to Lava
Extremely high temperature and pressure can cause the lower mantle to melt and become liquid rock, or magma. When a body of magma rises through the denser rock layers toward Earth's surface, some of it remains liquid. Magma that has reached the surface is called lava.
Lava Types
Magma comes in different "flavors," or compositions.
Each of these will produce a different lava, from fluid, fast-moving
basalt to slower, more viscous andesite. Because rocks are
made up of collections of minerals that melt at different
temperatures, the makeup of the rock being melted affects
the magma that results.
Viscosity
video clip (Quicktime, 39 seconds, 4,316K)
Take a look at two lava types: pahoehoe and slow, viscous aa.
[Read More About MELTING ROCKS]
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