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Abstract. Studying the retreat of the Patagonian Ice Sheet (PIS) during the last deglaciation represents an important opportunity to understand how ice sheets outside the polar regions have responded to deglacial changes in temperature and large-scale atmospheric circulation. At the northernmost extension of the PIS during the Last Glacial Maximum (LGM), the Chilean Lake District (CLD) was influenced by the southern westerly winds (SWW), which strongly modulated the hydrologic and heat budgets of the region. Despite progress in constraining the nature and timing of deglacial ice retreat across this area, considerable uncertainty in the glacial history still exists due to a lack of geologic constraints on past ice margin change. Where the glacial chronology is lacking, ice sheet models can provide important insight into our understanding of the characteristics and drivers of deglacial ice retreat. Here we apply the Ice Sheet and Sea-level System Model (ISSM) to simulate the LGM and last deglacial ice history of the PIS across the CLD at high spatial resolution (450 m). We present a transient simulation of ice margin change across the last deglaciation using climate inputs from the National Center for Atmospheric Research Community Climate System Model (CCSM3) Trace-21ka experiment. At the LGM, the simulated ice extent across the CLD agrees well with the most comprehensive reconstruction of PIS ice history (PATICE). Coincident with deglacial warming, ice retreat ensues after 19 ka, with large-scale ice retreat occurring across the CLD between 18 and 16.5 ka. By 17 ka, the northern portion of the CLD becomes ice free, and by 15 ka, ice only persists at high elevations as mountain glaciers and small ice caps. Our simulated ice history agrees well with PATICE for early deglacial ice retreat but diverges at and after 15 ka, where the geologic reconstruction suggests the persistence of an ice cap across the southern CLD until 10 ka. However, given the high uncertainty in the geologic reconstruction of the PIS across the CLD during the later deglaciation, this work emphasizes a need for improved geologic constraints on past ice margin change. While deglacial warming drove the ice retreat across this region, sensitivity tests reveal that modest variations in wintertime precipitation (∼10 %) can modulate the pacing of ice retreat by up to 2 ka, which has implications when comparing simulated outputs of ice margin change to geologic reconstructions. While we find that TraCE-21ka simulates large-scale changes in the SWW across the CLD that are consistent with regional paleoclimate reconstructions, the magnitude of the simulated precipitation changes is smaller than what is found in proxy records. From our sensitivity analysis, we can deduce that larger anomalies in precipitation, as found in paleoclimate proxies, may have had a large impact on modulating the magnitude and timing of deglacial ice retreat. This fact highlights an additional need for better constraints on the deglacial change in strength, position, and extent of the SWW as it relates to understanding the drivers of deglacial PIS behavior.
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Morphology, timing, and drivers of post‐glacial landslides in the northern Yellowstone region
Abstract The withdrawal of glaciers in mountainous systems exposes over‐steepened slopes previously sculpted by ice. This debuttressing can directly trigger mass movements or leave slopes susceptible to them by other drivers, including seismogenic shaking and changing climate conditions. These systems may pose hazards long after deglaciation. Here, we investigate the drivers of slope failure for landslides at the northern entrance to Yellowstone National Park, a critical conduit traversed by ~1 million visitors each year. Through field mapping and analyses of LiDAR data, we quantify the spatial and temporal relationships between eight adjacent slides. Stratigraphic relationships and surface roughness analyses suggest initial emplacement 13–11.5 ka, after a significant delay from Deckard Flats glacial retreat (15.1 ± 1.2 ka). Thus, rapid glacial debuttressing was not the direct trigger of slope failure, though the resultant change in stress regime likely had a preparatory influence. We posit that the timing of failure was associated with (1) a period of enhanced moisture and seismicity in the late Pleistocene and (2) altered stress regimes associated with ice retreat. Historical archives and cross‐cutting relationships indicate portions of some ancient slides were reactivated; these areas are morphologically distinguishable from other slide surfaces, with mean topographic roughness 2 times that of non‐active slides. Stream power analysis and archival records indicate Holocene incision of the Gardner River and human disturbances are largely responsible for modern reactivations. Our findings highlight the importance of combining archival records with stratigraphic, field and remote sensing approaches to understanding landslide timing, risk, and drivers in post‐glacial environments. This study also provides a valuable baseline for geomorphic change in the Yellowstone system, where a 2022 flood incised streams, damaged infrastructure and further reactivated landslide slopes.
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- Award ID(s):
- 2241214
- PAR ID:
- 10531898
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Earth Surface Processes and Landforms
- ISSN:
- 0197-9337
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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