Abstract
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 low temperatures facilitate long runout 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.
Plain Language Summary
Assessments of volcanic hazards in areas prone to small‐volume basaltic volcanoes includes consideration of the lateral extent of devastating pyroclastic surges from eruptions that are caused by magma‐water explosions. Previous assessments considered surge distances up to 6 km, but the deposits from Ubehebe Crater (Death Valley, California, USA) have been traced to 9 km and likely originally extended farther. This was not an unusual eruption, but its deposits are exceptionally preserved due to the arid environment. Pyroclastic surges from magma‐water explosions are likely to be cooler than other volcanic flows, and this facilitates long travel distances and hence far‐reaching potential impacts if the area is inhabited. We suggest that future assessments should consider pyroclastic surge distances of 10–15 km from the vent.
Key Points
Hazard assessments in monogenetic volcanic fields have considered pyroclastic surge runout up to 6 km based upon preserved deposits of previous eruptions
Surge deposits from Ubehebe Crater extend to 9 km; this may not be unusual and such surges may have long runout facilitated by their low temperatures
We suggest that future hazard assessments in monogenetic volcanic fields consider pyroclastic surge runout up to 10–15 km