Valle Grande, known to geologists as the Valles Caldera and the Jemez Caldera, is a scenic area in the Jemez Mountains of northern New Mexico in the United States. It is the south-east part of what remains of a very large volcano, or supervolcano, which erupted in ancient times and helped shape the Jemez Mountains.

In Mexican-accented Spanish, "Valle Grande" is usually pronounced "VYE-ay GRAHN-day", IPA //. Some people use pronunciations closer to Castilian Spanish.

History

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Until recently, it was part of the Baca Ranch, property of the Dunigan family; however, the owners sold the surface estate of 95,000 acres (380 km²) and seven-eighths of the geothermal mineral estate to the federal government, which is trying to find a way to let the public enjoy the land without spoiling it.

Valles Caldera National Preserve

On 25 July, 2000, The Valles Caldera Preservation Act, 16 U.S.C. Sections 698v-698v-10, created the Valles Caldera National Preserve. Noting that the careful husbandry of the Baca Ranch by its private owners, including selective timbering, limited grazing and hunting, and the use of prescribed fire, had preserved a mix of healthy range and timber land with significant species diversity, including New Mexico's largest herd of elk, thereby serving as a model for self-sustaining land development and use. 16 U.S.C. Section 698v(a)(5). Funds for the purchase came from the Land and Water Conservation Fund derived from royalties the US government receives from offshore oil and gas drilling ^*. The Preserve will have to produce sustaining income, under the Act; environmentalists had lobbied for the more inclusive protections of National Park status instead.

Geology & science

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Scientists are studying this area to learn about the fundamental processes in magmatism, hydrothermal systems, and ore deposition. With nearly 40 deep cores examined, resulting in extensive subsurface data, the Valles Caldera is the best explored caldera complex in the United States. It is the younger of two calderas in the region, having collapsed over and buried the Toledo Caldera (which might have collapsed over yet older calderas). These two large eruptions took place 1.4 million and 1 million years ago. The circular topographic expression of the Valles caldera measures 22 kilometers (14 miles) in diameter. The Jemez Volcanic Field, including the calderas, lies above the intersection of the Rio Grande Rift, which runs north-south through New Mexico, and the Jemez Lineament, which extends from southeastern Arizona northeast to the westernmost part of Oklahoma. The volcanic activity is related to the tectonic movements along this intersection.

The volcanic properties of the Valles Caldera make it a likely source for renewable and nonpolluting geothermal energy. However, some people oppose development of the geothermal energy, considering it destructive to scenic beauty and recreational and grazing use.[http://www.krqe.com/expanded.asp?RECORD_KEY%5BNews%5D=ID&ID%5BNews%5D=9427

The lower Bandelier tuff which can be seen along canyon walls west of the Valles Caldera, including San Diego Canyon, is related to the eruption and collapse of the Toledo Caldera. The upper Bandelier tuff is believed to have been deposited during eruption and collapse of the Valles Caldera. The now eroded and exposed orange-tan, light-colored Bandelier tuff from these events creates the stunning mesas of the Pajarito Plateau.

External links

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• U.S. Government's Valles Caldera website
• The Physics Institute of Brazil's Valles Caldera website (English)
• CNN archives: July 17, 2000
• Forests.org documents the negotiations that led to the Preservation Act
• Valles Caldera National Preserve
• Valles Caldera Coalition

VEI-7 volcanoes | Rift volcanoes | Volcanoes of New Mexico | Mountains of New Mexico | Craters of the United States | Volcanic calderas of the United States