Browsing by Author "Pantoja, S"

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    Imprint of recent Glacial Lake Outburst Floods (GLOFs) in Baker fjord sediments (Chile, 48 °S)
    (International Union for Quaternary Research (INQUA), 2019-07-30) Vandekerkhove, E; Bertrand, S; Reid, B; Saunders, KM; Kylander, M; Pantoja, S
    Glacial Lake Outburst Floods (GLOFs) constitute a major threat in glacier-covered regions. These catastrophic events occur when a lake dammed by a glacier or moraine suddenly empties, resulting in abrupt flooding. This issue is particularly pronounced in the Baker region (47 – 48 °S) of Patagonia, where 21 GLOFs have been documented in the last decade. During such events, the Baker River, which drains most of the eastern side of the Northern Patagonian Icefield, triples in discharge and suspended sediment concentrations increase by more than one order of magnitude. The recent occurrence and the vast impact of these large-scale events on the Baker River raises the question of how these events are recorded in Baker fjord sediments. The goal of this project is therefore to understand how GLOFs are registered in Baker fjord sediments, in order to reconstruct their occurrence in the past, i.e., when river discharge was not monitored. To do so, the bathymetry of the prodelta region of Baker fjord was mapped at high resolution and a total of ten sediment cores were collected. The sediment cores were described, photographed, and scanned at 2 mm resolution on a Geotek MSCL for magnetic susceptibility, gamma density, and spectrophotometry. Additionally, XRF scanning was performed at 2 mm resolution. A core chronology was established on the most promising core using 210Pb concentrations. Results show that the subaquatic delta in Baker fjord is deeply incised with well-developed sinuous channels (maximum depth of 26 m). The most prominent channel has an average width of 140 m and extends up to 8 km in Baker fjord. The morphology of the channels and the occurrence of sediment waves within the axial channels imply recent sediment transport by turbidity currents. The sediment cores, which display at least seven turbidites in a time span of 46 ± 7 years, confirm the occurrence of active turbidity currents. Although several potential triggering processes are plausible for the occurrence of dense underflows in Baker fjord and detailed monitoring of the subaquatic delta is required to pinpoint the exact triggering process(es), we believe that elevated river discharge during GLOFs is the main cause of the turbidite currents within the fjord. Although seasonal increases in river discharge due to snowmelt may trigger turbidity currents, it is more likely that the turbidites observed in the deepest sediment cores represent large-scale turbidity currents triggered by GLOFs. The lower number of turbidites in the sediment cores compared to the number of recent GLOF events however suggests that only the largest GLOFs are recorded as turbidites. This study demonstrates that GLOFs might be of key importance in shaping the fjord’s morphology, and that their occurrence in the past may be reconstructed using turbidite stratigraphy. © 2019 The Authors.