Where does volcanic ash come from?
JILL MASON
Dear Jill,
Ash comes from the explosive fragmentation of lava. Some magmas are gas
rich. When they approach the surface the gas begins to expand because
the pressure is lower. The gas bubbles continue to grow until they blow
the surrounding lava into small pieces. A reasonable analogy is shaking
up a bottle of soda and quickly removing the cap. The pressure of the
gas inside the bottle is high and forces the soda out. As it does, it
also blows the liquid into small droplets.
Steve Mattox, University of North Dakota
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