Browsing by Author "Torrejón, F"

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    Late Holocene Glacial Lake Outburst Floods (GLOFs) in Chilean Patagonia: evidence from Valle Grande floodplain sediments (47 °S)
    (International Union for Quaternary Research (INQUA), 2019-07-30) Vandekerkhove, E; Bertrand, S; Reid, B; Mauquoy, D; Saunders, KM; McWhethy, D; Stammen, S; Torrejón, F
    Glacial Lake Outburst Floods (GLOFs) constitute a major threat in glacierized regions. These catastrophic events occur when a lake dammed by a glacier or moraine empties, resulting in abrupt flooding. In Patagonia, this issue is particularly pronounced in the Baker region (47–48°S), where 21 GLOFs have been documented in the last decade. All recent GLOFs resulted from the emptying of Cachet 2 Lake into Colonia River, a tributary of the Baker River. During such events, Baker River, which is the largest in Chile draining most of the eastern side of the Northern Patagonian Icefield, triples in discharge. Due to backwater flooding, the water level in the Valle Grande floodplain, which is located along Baker river immediately upstream of Colonia River, rises by 4 to 6 meters, resulting in its complete inundation. Although GLOF frequency seems to have increased worldwide in the last decades, there is currently no reliable scientific evidence supporting this claim, largely due to a lack of flood records on timescales that extend beyond gauged river-flow datasets. To examine changes in GLOF frequency in Patagonia, four sediment cores were collected in the Valle Grande floodplain. The cores were scanned on a Geotek MSCL at 2 mm resolution for magnetic susceptibility (MS), gamma density, and sediment color (spectrophotometry). Loss-on-ignition was measured continuously at 5 mm resolution and radiocarbon ages, 210Pb concentrations, and charcoal counts were obtained to establish a core chronology. All cores indicate the occurrence of fine-grained organic-poor material with high MS and density values, alternating with organic-rich deposits. It is hypothesized that the fine-grained material is deposited during floods, whereas the organic-rich soils represent periods of quiescence. The records seem to display three periods rich in floods during the last 2500 years. Once precise age depth models are constructed, the results will be compared to historical records of climate and glacier variability to assess the possible relationship between GLOFs and climate change.
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    Neoglacial increase in high-magnitude glacial lake outburst flood frequency (Baker River, Patagonia, 47°S)
    (Copernicus GmbH, 2021-04-19) Bertrand, S; Vandekerkhove, E; Mauquoy, D; McWethy, D; Reid, B; Stammen, S; Saunders, KM; Torrejón, F
    Glacial Lake Outburst Floods (GLOFs) constitute a major hazard in periglacial environments. Despite a recent increase in the size and number of glacial lakes worldwide, there is only limited evidence that climate change is affecting GLOF frequency. In Patagonia, GLOFs are particularly common in the Baker River watershed (47°S), where 21 GLOFs occurred between 2008 and 2017 due to the drainage of Cachet 2 Lake into the Colonia River, a tributary of the Baker River. During these GLOFs, the increased discharge from the Colonia River blocks the regular flow of the Baker River, resulting in the inundation of the Valle Grande floodplain, which is located approximately 4 km upstream of the confluence. To assess the possible long-term relationship between GLOF frequency, glacier behavior, and climate variability, four sediment cores collected in the Valle Grande floodplain were analyzed. Their geophysical and sedimentological properties were examined, and radiocarbon-based age-depth models were constructed. All cores consist of dense, fine-grained, organic-poor material alternating with low-density organic-rich deposits. The percentage of lithogenic particles, which were most likely deposited during high-magnitude GLOFs, was used to reconstruct the flood history of the last 2.75 kyr. Results show increased flood activity between 2.57 and 2.17 cal kyr BP, and between 0.75 and 0 cal kyr BP. These two periods coincide with glacier advances during the Neoglaciation. Our results suggest that GLOFs are not a new phenomenon in the region. Although rapid glacier retreat is likely responsible for high GLOF frequency in the 21st century, high-magnitude GLOFs seem to occur more frequently when glaciers are larger and thicker.
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    Signature of modern meteorological and glacial lake outburst floods in fjord sediments (Baker River, Chilean Patagonia)
    (American Geophysical Union (AGU), 2021-12) Bertrand, S; Vandekerkhove, E; Liu, D; Renson, V; Kylander, ME; Saunders, KM; Reid, B; Torrejón, F
    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.