The 22-km-wide Valles caldera in northern New Mexico was formed during a series of major eruptions ending with the eruption of the Bandelier Tuff about 1 million years ago. Post-caldera uplift formed a large resurgent dome in the center of the caldera. The latest eruptions occurred about 130,000 years ago, but geothermal activity continues. This view from the caldera moat shows the rim of the 1.45 million-year-old Toledo embayment to the north, with the edge of the Cerro del Medio rhyolitic lava dome at the extreme left.

Photo by Lee Siebert, 1989 (Smithsonian Institution).

Additional Photos

Thick deposits of welded pumice form cliffs along the Jemez River valley SW of the Valles caldera, capping darker-red, bedded sedimentary rocks at the base of the canyon. The lowermost pyroclastic-flow deposit, showing pronounced columnar jointing, is the Otowi member of the Bandelier Tuff. The top of the section is the Tshirege member of the Bandelier Tuff. The two eruptions, about 1.45 and 1.1 million years ago, ejected about 600 cu km of magma and resulted in the formation of Valles caldera.

Photo by Lee Siebert, 1989 (Smithsonian Institution).

Soda Dam, along the Jemez River, is a travertine dam formed across a gorge in Precambrian granite-gneiss SW of the rim of Valles caldera. The travertine has been deposited over the past 5000 years by carbonated thermal waters discharged along the Jemez fault zone. About 15 hot springs related to the Valles caldera thermal system are found at this location.

Photo by Lee Siebert, 1989 (Smithsonian Institution).

Redondo Peak in the center and Redondito peak on the right are the eastern half of a resurgent dome in the center of the Valles caldera, seen from the SE across the caldera moat, Valle Grande. The uplifted resurgent dome is formed primarily of densely welded Bandelier Tuff that was uplifted about 50-100,000 years after formation of the caldera. Cerro La Jara, the small hill on the caldera floor at the middle left, is a small rhyolitic lava dome erupted along ring-fractures.

Photo by Lee Siebert, 1989 (Smithsonian Institution).

Volcanologists Bob Smith (left) and Roy Bailey (right) lead a geological field trip to Valles caldera. Redondo Peak at the upper right rises to 3430 m, 840 m above the caldera floor, and along with Redondo Border peak at the center, forms the western half of the uplifted resurgent dome seen at the center of the geologic map. The down-dropped Redondo Creek graben, which cuts diagonally through the center of the photo, has been the focus of geothermal exploration in the caldera.

Photo by Lee Siebert, 1989 (Smithsonian Institution).