My Neighbor, the Supervolcano

Living in a geothermally active area

Near Coyote, many agate shards along the dirt roads.

The Jemez Mountains area in the northern part of the Santa Fe National Forest in New Mexico is arguably one of the most exquisite regions of the state, at least according to the locals. Lush, alpine woodlands, pastoral mesas, and dark-red colored canyons and cliffs are the signature signs of the landscape. Coyote, the little village where I live, is in the northernmost district of the Santa Fe National Forest, and I am forever grateful for the majestic beauty all around me.

When you hike or walk around here, you’ll notice lots of pieces of agate, particularly along both sides of any unpaved forest roads. Many of them are covered with a thin, whitish film that hides the colors inside, but quite a number are cracked open, revealing browns, greys, or obsidian-black. My Rockhound’s Guide to New Mexico claims that there are also orange or red pieces, but I haven’t found one yet. I knew that these kinds of rock formations are of volcanic origin, but it surprised me to realize that they are part of a supervolcano that last erupted 1.2 million years ago and is now known as the Valles Caldera National Preserve. We often went hiking near Valle Grande (the most famous section of Valles Caldera) in the Jemez Mountains, but that’s really far away from Coyote — how did these agates end up here? I had to do some research.

Elk at Valles Caldera

Strictly speaking, “supervolcano” isn’t a scientific term. Geologists and volcanologists refer to a “Volcanic Explosivity Index” (VEI) of 8 and 7 when they describe super-eruptions. An increase of 1 indicates a 10 times more powerful eruption. VEI-8 are colossal events with a volume of 1,000 km3 (240 cubic miles) of erupted pyroclastic material (for example, ashfall, pyroclastic flows, and other ejecta). An example of a VEI-8 event is the eruption at Yellowstone (the Yellowstone Caldera) some 2.1 million years ago which had a volume of 2,450 cubic kilometers.  VEI-7 volcanic events eject at least 100 km3 Dense Rock Equivalent (DRE). Valles Caldera belongs to the VEI-7 class of supermassive events (accounting for the countless agates in and around my backyard) and is situated within the Jemez Volcanic Field. The last eruption and collapse of the Valles Caldera occurred 1.2 million years ago, piling up 150 cubic miles of rock and blasting ash as far away as Iowa. Although huge in volume, the caldera-forming eruption in the Jemez Mountains was less than half the size of that which occurred at the Yellowstone Caldera system some 631,000 years ago.

Satellite Image of Valles Caldera. NASA Earth Observatory, Public Domain

The name “caldera” comes from the Spanish word for “kettle”, “cooking pot”, or “cauldron”. Molten rock or magma begins to collect near the roof of a magma chamber bulging under older volcanic rocks. After an eruption begins and enough magma is ejaculated, the layer of rocks overlying the magma begins to collapse into the now emptied chamber because of the weight of the volcanic deposits. A roughly circular fracture develops around the edge of the chamber. In the case of Valles Caldera, the surrounding area continues to be shaped by ongoing volcanic activity, and an active geothermal system with hot springs and “fumaroles” (smoke plumes) exists even today.

Valle Grande

Much of northern New Mexico is geologically active. There are hot springs all over the place – Ojo Caliente Mineral Springs for example, where people can relax in pools which are fed from five different springs, each with a specific mineral content:  lithium, arsenic, iron and sodium/soda. The village of Jemez Springs has a number of hot springs and spas, some of which are on public land and can be reached via hiking trails, while others are commercial spas and bathhouses. Some friends who lived in Taos took me into the Rio Grande Gorge (some 800 feet from the rim down to the river) and we found several pockets on the river banks where the water was considerably warmer and clearly came from some hot spring. 

Ojo Caliente Mineral Springs Hotel, built in 1916, Public Domain

Maybe all the volcanic activity provides some release for seismic activity? When I moved to New Mexico in 2000, I somehow assumed that earthquakes didn’t happen here. I had experienced the Loma Prieta Earthquake in 1989; my daughter and I lived in Berkeley at the time. Although we didn’t suffer any damages whatsoever, not a single cup broke, not even one book fell off the shelf, the damage at the Nimitz Freeway in Oakland where entire sections of the upper deck of the freeway collapsed directly on the lower deck affected me for weeks. A section of the Bay Bridge collapsed as well. Several houses in the Marina district of SanFrancisco caught fire. I had lived through many earthquakes, both in the San Francisco-Bay Area and in Japan, but they had never caused any damage and didn’t bother me all that much. The one in 1989 was different because there was so much suffering and anguish. 

I was therefore quite relieved that New Mexico was earthquake-free. Or so I thought. And indeed, for over twenty years, there was no earthquake. But then on a Monday morning, July 12, 2021, a 4.3 magnitude earthquake rattled the area here, its epicenter only a few miles northwest from Coyote. And half an hour later, a 3.7 M tremor followed… It certainly brought back memories. 

Spruce and fir trees in the uplands

And it also made me ask: Will the Valles Caldera erupt again? While most of the media hype surrounding supervolcanoes focuses on Yellowstone where a VEI-8 event happened some 640,000 years ago which means that the next one could take place any moment or at least within the next 40,000 years, the Discovery Channel called Valles Caldera “a sleeping monster in the heart of New Mexico” but added in answer to the above question: No one knows. Duh.