Did You Know – November 2023

by | Oct 30, 2023 | Information, Newsletters

There is an active volcano in Sandoval County.  It is located in the Jemez Mountains.

Valles Caldera, Jemez Volcanic Field

Type: Ash-flow caldera, viscous domes, basaltic flows
Significance: One of the largest young calderas on Earth; type area for resurgent ash-flow calderas
Location: Valles Caldera, 35° 35′ to 36° 15′ N, 106° 10′ to 106° 48′ W; Sandoval County

When you drive or hike through the Jemez Mountains, you are looking at a landscape created by young volcanic eruptions. The Jemez Mountains are volcanic mountains; eruptions have continued intermittently from 14 million years ago to as recently as 40,000 years ago. The Valles Caldera is a supervolcano eruption, like Yellowstone, and one of the largest young calderas on Earth. It formed about 1 million years ago when multiple explosive eruptions occurred that produced an immense outpouring of ash, pumice, and pyroclastic flows. It is considered by geologists to be still active.

Instead of one big volcano, volcanic fields consist of clusters of many small volcanoes. Overall, they are all characterized by many small centers of eruption (one to a few kilometers across) of fundamentally basaltic, but ranging to more silica-rich compositions. The Jemez Volcanic Field, however, is different in that it began 14 million years ago as a normal volcanic field with the eruption of many small volcanoes and then experienced at least two extremely explosive caldera eruption events. The most recent of which, approximately 1.2 million years ago, formed the Valles Caldera and resulted in the eruption of the Bandelier Tuff, a thick ash flow unit that covers almost all of the earlier volcanic rocks from the field.

This type of volcanism has a slow tempo. Even though the caldera appears inactive because it is grown over with trees, it probably looked like that for most of its history. The presence of hot springs shows that the caldera is part of a large, long-lived, and still active system.

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