LATE HOLOCENE VOLCANISM IN AND ADJACENT TO MONO LAKE, CALIFORNIA

Mono Lake is a widely fluctuating, hydrographically closed body of hypersaline water that lies at the eastern base of California’s Sierra Nevada. On at least 10 occasions during the past 2000 years lake-bottom volcanism has given rise to spires, cones, domes, flows, and uplifted blocks of lake-bottom sediment that protrude above the water surface as islands. The age of these Mono Islands can be constrained using the presence/absence of well-dated tephra units from the nearby Mono Craters and Domes; the presence/absence of well-dated strandlines from the past fluctuations of Mono Lake; the presence, on some features, of ancient stumps that grew low on the shorelands during an extreme lake regression; and the presence of ejecta in radiocarbon-dated stratigraphic sequences. At least two islands--Java and the Negit core--existed prior to ~1700 cal BP; at least one additional eruption, creating the low Negit dome, occurred prior to ~1200 cal BP. A minimum of four eruptions took place between ~1200 and ~600 cal BP, and two more between ~600 and ~300 cal BP. The largest island in the lake, Paoha, is also the youngest, having been uplifted from the lake floor between C.E. ~1650 and 1700. The past 300 years is ominously remarkable for the apparent lack of island volcanism at Mono Lake.