Valles (Jemez) Caldera, New Mexico

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

Location: 35o 50' 40" N, 106o 57' 37" W.

About 1.2 million years ago, a huge mass of granitic magma intruded the crust of northern New Mexico. Instead of erupting as a volcano, however, when the magma approached the surface, the overlying rocks simply caved in. With the pressure on the magma suddenly released, gases like water vapor in the magma suddenly expanded, just like opening the top on a warm, shaken up can of soda. The magma erupted as gigantic pyroclastic flows, hot clouds of gas, ash, and pumice fragments.

In the scene here, north of the town of Jemez Springs, a sandstone hill (bright red) has been buried by hundreds of feet of ash (light pink and white). Several distinct ash layers are visible, but they were all erupted within a short time. Each individual layer took only a few hours or days to be deposited.

The collapse of the magma chamber roof left a huge circular depression, or caldera, which is prominent on satellite imagery. The center of the caldera is at about 35o 54 N, 106o 32'. The town of Los Alamos, famous for its atomic bomb research, is just east of the caldera. A lake filled the caldera until water crossed a low spot in the rim, then cut rapidly through the ash in a gigantic flood.

Original Scene

(author's image)

Possible Coloring

Figure With Features Labeled

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Created 30 June 2009, Last Update 15 January 2020