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Constraining the timing of the most recent cataclysmic flood event from ice-dammed lakes in the Russian Altai Mountains, Siberia, using cosmogenic in situ ¹⁰Be

¹ Department of Geography, University of Regensburg, Regensburg, Germany
² Department of Geography, University of Bonn, Bonn, Germany
³ Department of Geography, University of Zurich, and Particle Physics, ETH Zurich, Switzerland
⁴ Laboratory of Glaciolimnology, Tomsk State University, Tomsk, Russia
⁵ Paul-Scherrer Institute, Particle Physics, ETH Zurich, Switzerland
⁶ Department of Geography, University of Regensburg, Regensburg, Germany

Ice-dammed lakes were repeatedly formed in intermontane basins in the Russian Altai Mountains throughout the Pleistocene. These cataclysmic outburst floods, caused by ice-dam failures, were documented as Earth's largest flood waves by other geoscientists. Using in situ ¹⁰Be, we successfully dated surfaces of flood-associated boulders located in a former lake basin and downvalley from a former ice dam. Our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15.8 ± 1.8 ka. The field location of the boulders implies that they were deposited by the largest late Pleistocene flood that drained the Chuya-Katun Lake completely following initial dam failure. A published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers. The failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern Russia. This flooding event in the headwaters of the Ob River coincides with a freshwater peak as recorded in isotopic records of the Kara Sea and the Arctic Ocean.

Key Words: Altai Mountains • ¹⁰Be • outburst flood • paleolake