Abstract

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement.

Ubehebe craters, Death Valley, California, include over a dozen maar volcanoes formed primarily by phreatic eruptions of trachybasalt through a thick and permeable fanglomeratic sequence on the north slope of Tin Mountain.

Tuff derived from Ubehebe Crater, the largest crater in the area, is characteristically thinly bedded or laminated and was deposited by airfall and base-surge processes. Thick-bedded deposits showing evidence of mass flow occur where base surges were concentrated within, and followed gullies which had been carved into the fanglomerate prior to eruption.

Cross-bedded sequences were deposited by base surges that moved radially outward from Ubehebe Crater. They occur in the form of relatively small and large dunelike structures with spacing and morphologic features similar to antidunes and migration patterns somewhat similar to climbing ripples. The largest dunes in the area are composite structures that preserve a sequence of bed forms deposited in the high flow regime. Deposition apparently began in the antidune phase of the upper flow regime, progressing in time through sinuous lamination to plane beds as flow power decreased. Laminations are well developed and bed forms are preserved at each level within the composite structures because of a high rate of deposition and high sediment cohesion during flow of the base surges.

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