Tuesday - October 14, 2025

 6:00 p.m. to 8:00 p.m. PDT

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""The Volcanic Hazard in Nevada"

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By: Dr. Craig de Polo

Nevada Bureau of Mines and Geology (Retired)

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Abstract:​

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​Nevada is a tectonically active state with hundreds-of-thousands of historical earthquakes, hundreds of late Quaternary faults, and over 165 Quaternary volcanoes. Nevada’s volcanic hazard has historically been considered low. Although a review of Quaternary volcanism in the state has largely reenforced that idea, one area, the Lahontan Valley volcanic field has newly discovered information that may warrant a moderately high level of activity. There are seven Quaternary volcanic fields in Nevada. Most of Nevada’s volcanoes are monogenetic, meaning they only erupt once in their lifetime – so the volcanic fields themselves have to be viewed to judge eruptive activity. Two of these fields have not had an eruption in over a million years and can be considered inactive (Buffalo Valley and Western Nevada volcanic fields). Four volcanic fields have had late Pleistocene eruptions and can be considered still active (Lahontan Valley, Lunar Crater, Aurora, Southwest Nevada volcanic fields), and one field, Clayton-Columbus volcanic field, has a late mid-Quaternary eruption and can be considered potentially active. With exception of the Lahontan Valley and Lunar Crater volcanic fields, the hazard and potential consequences of an eruption in Nevada are low. The Lunar Crater volcanic field has a moderate hazard and low to moderate consequences, and can be considered as a moderate risk. But details about the Lunar Crater volcanic field indicate there may be long periods of time in the field between eruptions, and a low level of hazard probably describes the field best. In Lahontan Valley there are three Quaternary volcanoes at the surface. Rattlesnake Hill near Fallon was active between 2.5 and 0.9 Ma and can be considered as a polygenetic volcano, but it appears to be inactive. Upsal Hogback volcano erupted through 45 m of water of Late Pleistocene Lake Lahontan with a Surtseyan eruption and eventually formed Upsal Island. The volcano was later submerged by the lake. Earlier eruptions at the Upsal Hogback volcano have been proposed and there is circumstantial evidence for this, but it has not been documented. The eruption occurred between ~20 and 14 ka based on lake level curves. Recent work by Dr. Rodrigues at DRI has dated the youngest eruption at Soda Lake at 5 to 5.5 ka. Russell (1885) and Morrison (1964) posited that there was an earlier eruption at Soda Lake volcano in latest Pleistocene. This penultimate eruption has been documented during this study by the identification of a paleo-tuff ring with shorelines on it at the volcano. Recent dating by Dr. Rodrigues indicated this event occurred at 12.5 ±1.0 ka. The shorelines are from the Younger Dryas climatic event. The time since the most recent event (MRE) at the Soda Lake volcano is similar to the time between the MRE and the penultimate event perhaps suggesting we are do for an eruption, but there is not really a periodic eruption model for this kind of volcanism. The consequences for a Lahontan Valley eruption are high with potential impacts to Fallon, the Piute-Shoshone Reservation, two airports, two major highways, a railroad line, and numerous surrounding ranches and farms. With three events in the last ~20 ka and a mid-Holocene eruption, the level of risk of the Lahontan Valley volcanic field is moderately high.    

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BIO:

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Dr. Craig M. dePolo

Research Associate – Nevada Bureau of Mines and Geology

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Education:

B.S. Geology – California State University, Sacramento, 1976

M.S. Geology – University of Nevada Reno, 1986

PhD. Geology – University of Nevada, Reno, 1998

Work History:

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California Division Safety of Dams, 1976-1986

David B. Slemmons, Consultant, 1983-1986

Nevada Bureau of Mines and Geology, Research Associate, 1986-2025

University of Nevada, Reno, NBMG, Emeritus Faculty, May 2025

 

Craig dePolo has conducted research on California and Nevada historical earthquakes, latest Pleistocene and Holocene faults in Nevada, and Quaternary volcanoes in Nevada. He has mapped the geology of several quadrangles in the state and recently completed a major study on the earthquake hazards of Las Vegas Valley. Other projects include an earthquake planning scenario for western Nevada and documenting the effects of the 2008 Wells, Nevada (M6) and the 2020 Monte Cristo Range, Nevada earthquakes (M6.5). Craig also served on several state committees including the Nevada Earthquake Safety Council and the Nevada Hazard Mitigation Committee. Craig’s hobbies include photography, gardening, and blacksmithing.

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