Physical Volcanology and Hazard Analysis of a Young Monogenetic Volcanic Field: Black Rock Desert, Utah

The Black Rock volcanic cluster consists of 30 small volume monogenetic volcanoes. The volcanoes of this cluster have exhibited bimodal volcanism for \u3e 9 Ma. The most recent eruption of Ice Springs volcano ~600 yrs. ago along with ongoing geothermal activity attests to the usefulness of a hazard assessment for this area. The likelihood of a future eruption in this area is estimated to be between a 0.16 and 24% chance over the next 1 Ka (95% confidence). The explosivity and nature of many of these eruptions is not well known. In particular, the physical volcanology of Tabernacle Hill suggests a complicated episodic eruption. Initial phreatomagmatic eruptions at Tabernacle Hill are reported to have begun no later than ~14 Ka. The initial eruptive phase produced a tuff cone approximately 150 m high and 1.5 km in diameter with distinct bedding layers. Recent mapping and sampling of Tabernacle Hill\u27s lava and tuff cone deposits was aimed at better constraining the sequence of events, physical volcanology, and energy associated with this eruption. Blocks located on the rim of the tuff cone of were mapped and analyzed to yield preliminary minimum muzzle velocities of 60-70 m s-1. After the initial phreatomagmatic explosions, the eruption style transitioned to a more effusive phase that partially filled the tuff cone with a semi-steady state lava lake 200 m wide and 15 m deep. Eventually, the tuff cone was breached by the impinging lava resulting in large portions of the cone rafting on top of the lava flows away from the vent. Eruption onto the Lake Bonneville lake bed allowed the Tabernacle Hill lava flows to flow radially from the tuff cone and cover an area of 19.35 km², producing a very uniform high aspect ratio (100:1) flow field. Subsequent eruptive phases cycled several times between effusive and explosive, producing scoria cones and more lava flows, culminating in an almost complete drainage of the lava lake through large lava tubes and drain back