Ask Dr. Kaye - Is Mammoth Mountain an Active Volcano?

Ask Dr. Kaye - Is Mammoth Mountain an Active Volcano?


Ask Dr. Kaye - Is Mammoth Mountain an Active Volcano?


Map of Mammoth Lakes (shaded tan area below and left of center) in relation to the approximate outline of the Long Valley Caldera (broken red line) and the Sierra Nevada mountain range, eastern California, USA. The inset shows how ash from the Long Valley Caldera eruption spread all the way to Kansas.

Ask Dr. Kaye” will be a new weekly feature on Unofficial, where readers can submit earth science-based questions for Dr. Grant Kaye to answer. Grant is a geologist, cartographer, photographer, and skier based out of the Lake Tahoe area. Grant holds a PhD in Hazard and Disaster Management from the University of Canterbury in New Zealand, a Masters in Science in Geology from Oregon State University, and a Bachelor of Arts in Geology from Colorado College. His areas of scientific expertise are natural hazards, volcano geology, and earth science in general. Eruptions, earthquakes, and landslides are things he runs to, not away from.

Do you have a burning question in the realm of natural science that you’ve always wanted answered? Feel stuck on that GEO101 homework assignment?

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Technically, Mammoth Mountain is not an active volcano. According to the Smithsonian’s Global Volcanism Program, “active” is a description reserved for volcanoes that have erupted in the last 10,000 years (the Holocene), and the last eruption from Mammoth Mountain was ~57,000 years ago1. Still, there are signs of hot magma inside Mammoth Mountain, and there was a swarm of small earthquakes within Mammoth Mountain in 1989.  Scientists think the swarm resulted from a body of magma that rose up from deep in the earth and cracked rocks within the crust beneath mountain, but stopped before hitting groundwater and causing an eruption. This event is a good sign that there is still molten magma deep within the volcano, which could potentially be tapped for a future eruption. Also, large areas of trees killed by elevated levels of carbon dioxide in the soil from this magma lie on the SW side of Mammoth Mountain.

Areas of dead trees behind Mammoth Mountain (USGS Photo)

Mammoth also has a vent called a fumarole, where gases from hot magma inside the volcano rise up and are released into the air.  Tragically, three Mammoth ski patrollers died in April 2006 when a snow bridge over the fumarole collapsed and they fell in and were overcome by noxious gases.

Mammoth Mountain is just one part of a huge volcanic system called the Long Valley Caldera — a giant hole in the earth stretching from just northwest of Bishop, California from Lake Crowley to Glass Mountain (Figure 1). The hole was left when an enormous eruption took place ~760,000 years ago2, blowing enormous amounts of ash up into the air that you can still find today in soils in Kansas. Scientists think there is still hot mushy magma in a remnant magma chamber deep beneath the caldera3, evidenced by ground swelling in the middle of the valley, lots of small earthquakes, and numerous hot springs such as Hot Creek.

The youngest part of the Long Valley / Mammoth system is the Inyo chain of craters and domes, located less than a mile to the north of the town of Mammoth Lakes. The Inyo craters and domes are a linked chain of holes in the ground, holes filled with strange looking high mounds of shiny and very sharp obsidian lava; if you drive US395 south from Lee Vining towards Bishop and Mammoth Lakes, you are literally within 50 feet of them.

Glass Creek Dome (USGS Photo)

The Inyo craters lie in a NW-SE line just north of Mammoth Lakes, and cut through the “Scenic Loop” road (a.k.a. the “Escape Road”). The craters get progressively younger as you go along the chain towards Mammoth Lakes, and the youngest (and closest to Mammoth lakes) was formed only ~650 years ago4. Each of these domes was formed by a series of eruptions in which a sheet of hot magma (called a dike) actually made it to the surface of the earth, hit groundwater, and caused a sizeable explosion. Some in the chain are craters that had an explosion without erupting any lava, and some are domes that had an explosion followed by thick lava oozing  out onto the surface; the lava would fill the crater, squeeze up and out like a thick toothpaste, and eventually form the domes that are still there today.

Panum Crater (USGS Photo)

There is also another chain of craters and lava domes just to the NE of the Inyo craters by Mono Lake. The so-called Mono craters had eruptions as recently as the 1800s, specifically in Panum Crater.

But back to the initial question: Yes,  there are plenty of examples of magma-derived volcanic activity in, on, and around Mammoth Mountain, even if it hasn’t had an actual eruption in the last 10,000 years. Could it erupt again? The answer is a very tentative yes, but the likelihood of that happening is probably very small and it wouldn’t take place without ample warning signs.

Next week I’ll answer the question – “what would happen to California if the Hayward fault ruptured in a Mw 7+ earthquake?”

References (and for more reading):

1 – Hildreth W (2004) Volcanological perspectives on Long Valley, Mammoth Mountain, and Mono Craters: several contiguous but discrete systems. J. Geophys. Res. 136:169–198

2 – Bailey R, Dalrymple G, and Lanphere M (1976) Volcanism, structure, and geochronology of Long Valley Caldera, Mono County, California, Jour. of Geophysical Research 81 no. 5, p. 725-744

3 – Hill D, and Prejean S (2005). Volcanic unrest beneath Mammoth Mountain, California. Journal of Volcanology and Geothermal Research 146: 257–283

4 – Miller C (1985) Holocene eruptions at the Inyo volcanic chain, California; implications for possible eruptions in Long Valley Caldera. Geology 13: 14–17

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