Signature of Modern Meteorological and Glacial Lake Outburst Floods in
Fjord Sediments (Baker River, Chilean Patagonia)
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.