JOHN R. FOSTER / SCIENCE PHOTO LIBRARY JOHN R. FOSTER / SCIENCE PHOTO LIBRARY
Pumice collected near Crater Lake National Park in central Oregon. This pumice is from the eruption and caldera collapse of 12,000 ft, Mt. Mazama 7,600 years ago which led to the formation of Crater Lake. This form of volcanic rock is a result of powerfully explosive eruptions as indicated by the very porous structure that trapped volcanic gases. Pumice is so low density it easily floats on water.
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