Desert Diary
April 9, 2003

Geology/Caldera

   

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Much of the northern Chihuahuan Desert has been affected by volcanism, and many inhabitants are well aware of various aspects of this volcanic activity. Indeed, the University of Texas at El Paso, built on the igneous Campus Andesite, looks across the pass excavated by the Rio Grande to the volcanic Cerro de Muleros on the west.

Calderas are one of the more spectacular types of formations produced by volcanism, and the northern Chihuahuan Desert region is home to several. Most date back to the Oligocene, more than 30 million years ago. The name comes from the similarity in shape to the pot used for boiling water--a large, sunken area. Calderas usually are formed by one of two ways: by an explosive eruption that literally blows away the surface of the earth or by the eruption from below of so much lava or ash that the ground collapses. Widespread deposits of once incandescent Oligocene volcanic ash attest to the transfer of great volumes of rock from below, suggesting that the collapsing earth surface was the least of Oligocene dangers.

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.

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