California’s exposure to volcanic hazards

Abstract

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Stratigraphy and eruption history of maars in the Clear Lake Volcanic Field, California

“…Residents, infrastructure, agricultural, water, and recreational resources would be at significant risk in the event of explosive phreatomagmatic activity. Additionally, any explosive eruptions in the Clear Lake area have the potential to disrupt major transportation routes and create tephra hazards that affect air traffic in the Bay Area and beyond (Mangan et al, 2019).…”

“…place CLVF maar eruptive activity firmly in the Holocene period, though it is unknown whether future dates will place any eruptions within the past 2,000-3,000 years (indicating a higher-threat volcano following the ranking scheme of Ewert et al, 2005). These ages, in combination with the populations, infrastructure, and transportation routes at risk in the CLVF (Abdollahian et al, 2018;Mangan et al, 2019), reinforce the need for monitoring and hazard assessment. Worldwide, hazards from phreatomagmatic explosions, such as base surges, lahars, and tsunamis, have produced about 20% of all fatalities associated with volcanic activity in historical time (Mastin and Witter, 2000).…”

“…The Whakaari, New Zealand, eruption of 2019 (Dempsey et al, 2020) illustrates the devastating consequences of being in close vicinity to even relatively small phreatic eruptions. Additionally, maar eruption cloud heights of 6,000+ m and associated ashfall (Ort et al, 2018) have the potential to disrupt regional populations, infrastructure, and transportation (including air traffic) given the proximity of the CLVF to the cities of Lakeport, Clearlake, Ukiah, Santa Rosa, and Napa (Abdollahian et al, 2018;Mangan et al, 2019). The association of known CLVF maar craters (and potentially more beneath the lake) with faults also suggests that future eruptions may occur preferentially along faults.…”

“…The rocks can be divided into four rough temporal groups: 1.3-2.1 Ma (basalt and basaltic andesite lavas, dacite and rhyolite lava flows and tuffs), 0.8-1.1 Ma (dacite and rhyolite flows and tuffs), 0.30-0.65 Ma (dacite and rhyolite lava flows), and 0.01-0.1 Ma (basaltic andesite scoria cones and maars) (Donnelly-Nolan et al, 1981). This volcanism was fed by a silicic magma source whose magmatic heat still supplies the Geysers geothermal field (Figure 1B) (Hearn et al, 1981;Donnelly-Nolan et al, 1993;Stanley and Blakely, 1995;Mangan et al, 2019), as well as by periodic injections of more mafic magmas from deeper mantle sources (Hearn et al, 1981).…”