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Desert Diary


Things that seem crazy at first sometimes make sense after a bit of thought. How often have we heard of "walking on water" used for the ridiculous? Yet, a moment's thought tells us that it's done all the time in cold climates—after all, what is ice if not water? A floating rock also seems silly--yet there are indeed rocks that will ride the waves as nimbly as any boat. In fact, there are parts of the Chihuahuan Desert where such light-weights abound.

Deep underground, the molten rock we call magma contains, thanks to the immense pressures, large amounts of dissolved gases. Lava consists of magma reaching the surface during volcanic activity. If the load of gases is high and the pressure released abruptly, as in a violent eruption, the effect is much like uncapping a shaken can of carbonated soft drink. The fizzing creates huge numbers of bubbles. Splattered far into the sky, pieces of lava quickly cool, and the bubbles are trapped. The result? The rock, pumice—the floatable rock made mostly of air.
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Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.



Web Resources

On Pumice from about.com. Good photos.

Volcanic Materials--Terminology, from the USGS.