Valles Caldera and the Bandelier Tuff

A caldera occurs when there is a volcanic collapse creating a crater. Most craters are formed by deposition around a volcanic vent, and enlarged by the slumping of unstable deposits into the vents. Calderas on the other hand are formed when there are infrequent eruptions, usually very large, from depths ranging from 4-7 kilometers. The remaining void space is then filled by the collapse of the surrounding area. The caldera is usually filled with its own ash, and pumice. Calderas also vary in size; they range from being at small as 1.7km in diameter all the way to the largest known caldera, which is 48km in diameter. The Valles Caldera, located in the Jemez Mountains in New Mexico is type of caldera known as a resurgent caldera. A resurgent caldera occurs when gas-rich magma collects near the top of a magma chamber creating a bulge. After eruption begins and the collapse is initiated, ring shaped fractures being in the magma chamber and burst to the surf

There are also geo-politics that surround the Valles caldera that must be brought up. Up until President Clinton signed the Valles Caldera Preservation act, and the government bought the Valles caldera for one hundred and one million dollars, the ranch had belonged to James D. Dunigan who bought the piece of land in 1962. From then on the ranch was known as the Baca Ranch. There are also reasons that the purchased was criticized, one being that when Dunigan purchased the land in ’62, he paid little over two million dollar. Another big criticism about the purchase is that it got a bad evaluation being that the person doing the evaluation only took into account retail value based off natural resources and what not, not the geological importance of the valles Caldera itself. Also, when James Dunigan dies in 1980, the sale of the Valles Caldera halted, making the acquisition of it even tougher, and it took much longer, just close to twenty years on July 25th, 2000 when the United States government finally purchased it.

When the caldera did erupt it spewed out more that three hundred cubic kilometers of ash mostly known as the Bandelier tuff. The tuff flowed from the caldera at a rate of over one hundred kilometers an hour and cover

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