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

Abstract

About 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.

Anthropogenic climate change has altered lake state in the Sierra Nevada (California, USA)

“…While the region experienced Late Holocene volcanic eruptions and earthquakes, little evidence exists in seismic reflection profiles for sublacustrine faulting or doming in June Lake, as has been observed at nearby Mono Lake (Colman et al, 2014;Lyon et al, 2019). Furthermore, glacial erosion associated with the Little Ice Age (LIA; Gillespie & Clark, 2011) is unlikely to have modified June Lake's exposure to prevailing winds from the west-southwest or to have degraded water clarity with rock flour (Clark & Gillespie, 1997).…”

Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

“…However, there had been no systematic study of the degassing features in and around the Mono Craters chain. The most recent eruptions and intrusion-related uplift occurred at Paoha Island in Mono Lake about 300 years ago (Stine, 1987;Kelleher and Cameron, 1990;Colman et al, 2014). Despite decades of studies focused on the input of gas to Mono Lake (Broecker and Wanninkhof, 2007), no gas flux measurements have been attempted at the exposed subaerial volcanic vents on the island.…”

Constraining the Early Eruptive History of the Mono Craters Rhyolites, California, Based on 238U‐230Th Isochron Dating of Their Explosive and Effusive Products

“…Beneath the Mono Craters chain, geophysical data suggest the presence of as much as 20% silicic melt (Achauer et al, ; Dawson et al, ; Peacock et al, ), which is inferred as part of a granitic reservoir that has fed the eruptions of high‐silica rhyolite at Mono Craters (Hildreth, ). The area with the youngest silicic volcanism (dacites to low‐silica rhyolites) is centered in Mono Lake where intrusive, effusive, and explosive events formed the islands of Negit and Paoha between about 2000 and 350 years ago, respectively (Figure a; Colman et al, ; Stine, ). Ongoing emission of magmatic fluids (CO 2 and He) near the northern end of the Mono Craters and along the southern part of Mono Lake suggests continued degassing of intruded basaltic magma (Bergfeld et al, ), inferred to sustain silicic magmatism in the entire Mono Lake‐Long Valley region (Hildreth, ).…”