Downwind deposits of ash produced by an explosive eruption could reach thicknesses of at least 20 cm at a distance of 35 km (8 in. at 22 mi), 5 cm at a distance of 85 km (2 in. at 53 mi), and about 1 cm at a distance of 300 km (0.5 in. at 185 mi).
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These estimates of potential ash thicknesses are based on deposits of ash from past eruptions at other volcanoes that involved volumes of as much as 1 km3 (0.25 mi3). Only a part of an ash-fall hazard zone would probably be affected by any single ash fall; the part affected would be determined by the wind speed and direction or directions during an eruption.