Signature of modern meteorological and glacial lake outburst floods in fjord sediments (Baker River, Chilean Patagonia)
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Date
2021-12
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Publisher
American Geophysical Union (AGU)
Abstract
Floods are among the most destructive natural hazards on Earth. In paleohydrology, sediments are generally considered as one of the best archives to extend flood records to pre-historical timescales. Doing so requires being able to identify flood deposits from sediment archives and decipher between flood types. The latter is particularly important in glacierized regions, where meteorological floods frequently co-occur with Glacial Lake Outburst Floods (GLOFs). In Patagonia, GLOFs are particularly pronounced in the Baker River watershed (48°S), where 23 events occurred between 2008 and 2020. Since 1976, the same region experienced three intense rain-on-snow events. To identify the sedimentary signature of these flood events, ten sediment cores collected in the fjord immediately downstream of the Baker River (Martínez Channel) were investigated and compared to the recent flood history of the river. Results show that sediments accumulate on the fjord head delta at 2.0 to 3.4 cm yr-1 and that GLOF deposits can be distinguished from background sediments by their finer grain size (5.98 ± 0.82 μm) and lower organic carbon content (0.31 ± 0.06%), reflecting the release and transport in suspension of high amounts of glacial rock flour. Our results also show that the rain-on-snow events that occur in summer, and therefore primarily affect the glacierized part of the watershed, have the same sedimentary signature as GLOFs. In contrast, rain-on-snow events occurring in winter have a distinct coarse and organic-rich signature, reflecting sediment input from the non-glacierized part of the watershed. In summary, this study shows that (a) GLOF deposits in fjord sediments are distinct from typical flood turbidites and are best identified by their low grain size and total organic carbon content, and (b) the sedimentary signature of rain-on-snow floods in partially glacierized watersheds depends on the season during which they occur. We anticipate that our findings will contribute to a better interpretation of flood records from partially glacierized watersheds.
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Keywords
Glaciers, Lakes, Floods, Chile, Rivers, Sediments, Watersheds
Citation
Bertrand, S., Vandekerkhove, E., Liu, D., Renson, V., Kylander, M. E., Saunders, K. M., Reid., B., & Torrejón, F. (2021). Signature of modern meteorological and glacial lake outburst floods in fjord sediments (Baker River, Chilean Patagonia). Poster presented to the AGU Fall Meeting 2021, New Orleans, Louisiana and Online, 13-17 December 2021. In AGU Fall Meeting Abstracts (Vol. 2021, PP45E-1141). Retrieved from: https://agu.confex.com/agu/fm21/meetingapp.cgi/Paper/888574