The effects of recent uplift and volcanism on deposition in Mono Lake, California, from seismic‐reflection (CHIRP) profiles

Abstract

AbstractAbout 150 km of high‐resolution, seismic reflection (Compressed High‐Intensity Radar Pulse) profiles (approximately 20 m penetration) were collected in Mono Lake in order to define the uppermost sedimentary architecture of the basin, which has been heavily impacted by recent volcanic, tectonic, and climatic processes. The study also provides an important background for ongoing efforts to obtain paleoenvironmental records from sediment cores in the lake. The history of four seismic‐stratigraphic units in the upper 20 m of section are inferred from the data, and the interpretations are generally consistent with previous interpretations of lake history for the past 2000 years, including a major lowstand at 1941 m. No shorelines below the previously documented major lowstand at 1941 m were found. A relatively steep slope segment, whose toe is at about 1918 m, and which occurs on the southern and western margins of the deep basin of the lake, is interpreted as the relict foreset slope of deposition from prograding western tributaries. This topography is unconformably overlain by a unit of interbedded tephra and lake sediments of variable lithology, which contains tephra of the North Mono (600–625 cal yr BP) eruption in its upper part. The tephra‐rich unit is overlain by a mostly massive mudflow deposit that is locally more than 18 m thick and that is distributed in a radial pattern around Paoha Island. The evidence suggests that within the past few hundred years, rapid uplift of Paoha Island through thick, preexisting lake deposits led to widespread slope failures, which created a terrain of disrupted, intact blocks near the island, and a thick, fluid mudflow beyond. As is common in mudflows, the mudflow moved up the depositional slope of the lake floor, terminating against the preexisting slopes, likely in multiple surges. Since about 1700 Common Era, fine‐grained, well‐laminated sediments have accumulated in the deep parts of the lake at anomalously rapid rates, probably driven by continued rapid, small‐scale shedding of sediment from Paoha Island.