Lateral extent of pyroclastic surge deposits at Ubehebe Crater (Death Valley, CA) and implications for hazards in monogenetic volcanic fields

Hazard assessments in monogenetic volcanic fields require estimates of the runout of pyroclastic surges that result from phreatomagmatic explosive activity. Previous assessments used runout distances of 1-4 km, with large cases up to 6 km. Surge deposits at Ubehebe Crater (~2100 y.b.p., Death Valley, California) have been traced ~9 km from the crater center, and likely originally extended 1-3 km farther. There is no evidence that the Ubehebe Crater activity was unusually energetic; rather, its distal deposits are better preserved than those at most maar volcanoes because of its young age and the arid environment. Numerical simulations illustrate how long runout is facilitated by low temperatures of phreatomagmatic surges due to reduced expansion of entrained air compared to hot surges, allowing cool surges to retain higher densities than ambient air. We suggest that hazard assessments for volcanic fields with phreatomagmatic, maar-forming eruptions should consider runout distances in the range of 10-15 km.