The Behavior of Magma
Why do some volcanoes explode violently while others erupt gently? Why do some kinds of magma (molten rock) solidify within Earth to form hard rocks, and others rise all the way to the surface to erupt from volcanoes as lava? To answer these questions, we must consider the properties and behavior of magma. Once magma forms, it rises toward Earth’s surface because it is less dense than surrounding rock. As it rises, two changes 0ccur. First, it cools as enters shallower and cooler levels of Earth. Second, pressure drops because the weight of overlying rock
decreases. Cooling and decreasing pressure have opposite effects on magma: Cooling tends to solidify it, but decreasing pressure tends to keep it liquid.
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