Characterization of Tephra Fall Deposit at Lunar Crater Volcanic Field, Nevada

Explosive volcanic eruptions pose well-established hazards to aviation and public health. One possible source for explosive eruptions is basaltic monogenetic scoria cones. Although generally regarded as a well-understood eruptive style, few data have been collected of tephra deposits from prehistoric scoria cone eruptions. This project focused on a 38 ka eruption at Lunar Crater Volcanic Field, NV, which produced a tephra fall deposit visible up to 6 km from the source vent. A total of 28 sample sites were characterized for depth, largest grainsmaximum grain size, and scoria texture. A sample was collected at each site for laboratory determination of deposit density and, based on that, mass per area. Field data indicate that the deposit contains two beds which were likely produced by two separate phases of the eruption. We focused on the topmost bed due to its greater lateral extent, and the consequent interpretation that resulted from a higher plume. Reconstruction of the eruption column based on mass per unit area is presently being undertaken to ascertain plume height and windspeed, but preliminary results based on grain size suggest an eruption column between 6 and 8 km in elevation with a 25 m/s wind blowing to the northeast. Modeling undertaken in subsequent months will be used to analyze hazards posed by future eruptions to downwind interests, especially aircraft.