Signature of modern glacial lake outburst floods in fjord sediments (Baker River, southern Chile)

Abstract

Glacial Lake Outburst Floods (GLOFs) constitute a major hazard in glacierized regions. They are particularly pronounced in the Baker River watershed (Chilean Patagonia, 48°S), where 23 events occurred between 2008 and 2020. Although GLOF deposits have previously been studied in lake settings, how modern GLOFs are recorded in fjord sediments remains mostly unknown. To address this issue, ten sediment cores collected in the fjord immediately downstream of the Baker River (Martínez Channel) were investigated and compared to the recent GLOF history of the river. Results show that sediments accumulate at 2.0 to 3.4 cm year −1 and that GLOF deposits can be distinguished from background sediments by their finer grain size (5.98 AE 0.82 μm) and lower organic carbon content (0.31 AE 0.06%), reflecting the release and transport in suspension of high amounts of glacial rock flour during GLOFs. Although 21 GLOFs from Cachet 2 Lake occurred between 2008 and 2017, the first events left a stronger imprint in the sediment, suggesting that more sediment of glacial origin was released during those initial events, possibly due to lake-bed erosion. An older GLOF deposit was tentatively linked to the outburst of Las Lengas Lake in 1988. The sediment cores also contain fine-grained turbidites, especially in the prodelta area. These turbidites confirm recent channel activity, but most of them seem to have been triggered by processes other than GLOFs. Overall, the results of this study suggest that GLOF deposits are distinct from typical flood turbidites. They are best identified by their low grain size and total organic carbon content, and best archived on the delta slope, away from any submarine channel influence. Finally, these results highlight the potential of fjord sediment archives to establish pre-historical GLOF records and ultimately improve GLOF hazard assessments.

Provenance of Baker River sediments (Chile, 48°S): Implications for the identification of flood deposits in fjord sediments

“…Local testimonies and satellite images also indicate the existence of a GLOF from proglacial lake Las Lengas, in the los Ñadis valley (Figure 1), in March 1988 (Iribarren Anacona et al, 2014; Vandekerkhove et al, 2021). This event resulted in a significant increase in the discharge of los Ñadis River (Iribarren Anacona et al, 2014), but its signature in the Baker River hydrographs is unclear, possibly due to their low temporal resolution (one measurement daily; Vandekerkhove et al, 2021).…”

“…Due to relatively high year‐round precipitation and the presence of large icefields and mountain glaciers, this region is also prone to meteorological floods driven by extreme precipitation, high seasonal meltwater discharge and rain‐on‐snow events (Dussaillant et al, 2012; Vandekerkhove et al, 2021). Two particularly large rain‐on‐snow events occurred in December 1976 and December 1989 (Dussaillant et al, 2012).…”

“…Dussaillant et al, 2010; Harrison & Winchester, 2000; Jacquet et al, 2017). However, recent studies indicate that at least one historical GLOF within the Baker River watershed originated from a smaller moraine‐dammed lake not related to the NPI (Iribarren Anacona et al, 2014; Vandekerkhove et al, 2021).…”

“…One of the best archives of Baker River floods are the sediments deposited in the fjord immediately downstream of the Baker River (Martínez Channel). Based on a comparison of sedimentological data with historical chronicles, Vandekerkhove et al (2021) showed that the 21st‐century GLOFs originating from Lake Cachet II were recorded in the fjord's sediments as fine‐grained and organic‐poor deposits. This is in contrast with the common idea that floods are consistently recorded in sediments as turbidites (e.g.…”

Seasonal Variations in Fjord Sediment Grain Size: A Pre‐requisite for Hydrological and Climate Reconstructions in Partially Glacierized Watersheds (Baker River, Patagonia)

“…(b) Temporal variations in log (EM 1 /EM 2 ) compared to mean annual baseflow and temperature in the lower Baker watershed(Alvarez-Garreton et al, 2018). The age-depth model of fjord sediment core FC17-08 is fromVandekerkhove et al (2021).…”