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The glacial geology community has developed digital reconstructions of Pleistocene glaciers in the western U.S. through decades of regionally focused research and interpretations of geologic maps. These paleoglacier reconstructions afford an opportunity to develop paleoclimate reconstructions for the Late Quaternary in the western U.S., especially when combined with cosmogenic chronologies and other paleoclimate proxies and model output. Here, we present a geospatial database of Late Pleistocene mountain glaciers for the conterminous western U.S. based on compilations of paleoglacier reconstructions spanning glaciated mountains in the region. The database consists of paleoglacier outlines as georeferenced polygons drawn at scales ranging from 1:24,000 to 1:100,000, reflecting differences in available mapping data and degrees of confidence in identifying glacial deposits and landforms used to identify paleoglacier limits. The database is available as a web feature service designed to be easily represented in a geographic information system or web mapping application to enable visualization of the pattern of Late Pleistocene mountain glaciation and analysis of paleoglacier outlines and derivative products, such as equilibrium-line altitudes and boundaries of modeled paleoglaciers. We illustrate potential applications of the database for visualization and data assimilation with an example from mountains neighboring the Lake Bonneville basin, where paleoglacier outlines are based on 1:24,000 scale mapping of glacial deposits and landforms and cosmogenic chronologies of moraines are abundant. For this research, the database enables an analysis of the pattern of glaciation in the region and, through assimilation with chronological data, an assessment of the relative timing of glacier maxima and the time when Lake Bonneville overflowed. While the database can be easily shared among users and represented in a geographic information system, development of the database requires community input to maximize its utility for users across disciplines. A goal of this presentation is to encourage interested users to share ideas for developing an accessible, scalable, and community-supported database of paleoglaciers. 

Important information about past climates can be determined from reconstructed equilibrium line altitudes (ELA) of mountain paleoglaciers, specifically the temperature and precipitation accompanying a glacier in equilibrium. Previous reconstructions of Late Pleistocene ELAs of mountain glaciers across the western United States have been used to infer the pattern of temperature and precipitation change across the region, although most of the work was based on presumed ages and limited mapping of glacial deposits and landforms. Cosmogenic nuclide exposure dating of moraines combined with updated mapping and aerial imagery afford an opportunity to revisit the pattern of regional ELAs during multiple episodes of the last Pleistocene glaciation. The goal of this research is to reconstruct ELAs in the same region of previous reconstructions based on glacial sediments that have been dated using cosmogenic nuclide exposure ages. We focus on the large number of glacial valleys with moraines corresponding to the Last Glacial Maximum (LGM; 26.5-19.0 ka). Paleo-ELAs are estimated using the toe to headwall altitude ratio and the accumulation area ratio determined from published glacier reconstructions and existing glacial mapping. Cosmogenic-exposure ages of moraines are compiled from the informal cosmogenic nuclide exposure age database for alpine glacial features (ICE-D Alpine) and represented in a geographic information system along with ELAs for each glacial valley. A reconstructed ELA surface spanning the conterminous western United States is produced using existing algorithms in ArcGIS. Results show reconstructed ELAs generally lower than initially estimated and a larger range of ELAs across the region. In the Sierra Nevada, ELAs increase southeastward, which is consistent with previous estimates, spanning a range from 1800 to 2800 m asl. ELAs rise eastward across the Basin and Range toward the western shore of the area covered by Lake Bonneville, and then decrease eastward toward the Wasatch Mountains. This pattern is inconsistent with previous estimates and may reflect a west-to-east precipitation gradient that differs from modern climate. We discuss this pattern and broader features of the ELA surface of the LGM and later episodes of the last Pleistocene glaciation. 

Abstract Rock glaciers are common in alpine landscapes, but their evolution over time and their significance as agents of debris transport are not well‐understood. Here, we assess the movement of an ice‐cemented rock glacier over a range of timescales using GPS surveying, satellite‐based radar, and cosmogenic¹⁰Be surface‐exposure dating. GPS and InSAR measurements indicate that the rock glacier moved at an average rate of ∼10 cm yr⁻¹in recent years. Sampled boulders on the rock glacier have cosmogenic surface‐exposure ages from 1.2 to 10 ka, indicating that they have been exposed since the beginning of the Holocene. Exposure ages increase linearly with distance downslope, suggesting a slower long‐term mean surface velocity of 3 ± 0.3 cm yr⁻¹. Our findings suggest that the behavior of this rock glacier may be dominated by episodes of dormancy punctuated by intervals of relatively rapid movement over both short and long timescales. Our findings also show that the volume of the rock glacier corresponds to ∼10 m of material stripped from the headwall during the Holocene. These are the first cosmogenic surface‐exposure ages to constrain movement of a North American rock glacier, and together with the GPS and satellite radar measurements, they reveal that rock glaciers are effective geomorphic agents with dynamic multi‐millennial histories. 

Abstract Twenty-one sediment cores were obtained from 20 lakes in the Uinta Mountains, Utah, USA. Depth-age models were developed using 14C dating, and sediments were analyzed for loss-on-ignition (LOI), carbon-nitrogen ratio (C:N), and grain size distribution. Although some of these cores have been considered individually in previous studies, here the entire set of cores is evaluated collectively to identify consistent patterns, commonalities, and trends in the post-glacial interval. All lakes accumulated substantially greater amounts of submicron-size clastic material before ca. 9.5 ka BP. This pattern is interpreted as a signal of prolonged landscape instability following deglaciation. Values of LOI and C:N exhibit a strong, positive correlation in nearly all lakes, indicating that organic matter accumulation is controlled by the influx of terrestrial material. In the six lakes exhibiting the strongest correlation, and featuring the most robust inflowing streams, median grain size and the abundance of sand increased between 10 and 6 ka BP, simultaneous with increases in LOI and C:N. This correspondence is interpreted as evidence for frequent high-intensity storms during the early Holocene, likely driven by enhanced monsoonal circulation. The early parts of five of the records contain a sharp increase in LOI. Lakes exhibiting this pattern are typically smaller and shallower, and are located in less rugged watersheds. Finally, all six cores from the western Uinta Mountains contain evidence for an environmental perturbation ca. 4.5 ka BP. Although the nature of this event is unclear, these lakes accumulated notably finer-grained sediment with less organic matter at this time. This analysis illuminates the post-glacial history of this strategically located mountain range, and underscores the value inherent in analyzing cores from multiple lakes when reconstructing paleoclimatic history. 

ABSTRACT This study uses a hydrologic‐balance model to evaluate the range of precipitation and temperature (P‐T) conditions required to sustain Lake Bonneville at two lake levels during the late Pleistocene. Intersection with a second set of P‐T curves determined from glacial modelling in the nearby Wasatch Mountains places tighter climatic constraints that suggest gradually increasing wetness from ~21 to 15 ka. Specifically, during the latter part of the Last Glacial Maximum (LGM) (~21–20 ka), Lake Bonneville approached its highest level under conditions roughly 9.5°C colder but only 7% wetter than modern. As the lake reached its pre‐flood Bonneville level (~18.2–17.5 ka), climate conditions were ~16% wetter and ~9°C colder than modern. Byca. 15–14.8 ka, Lake Bonneville abandoned the overflowing Provo level under conditions that were ~21% wetter and ~7°C cooler. These results suggest that regional LGM highstands were not caused by large increases in precipitation, but rather by a climatic optimum in which moderate wetness combined with depressed temperatures to create a positive hydrologic budget. Later highstands during Heinrich I from 17 to 15 ka were likely achieved under gradual increases in precipitation, prior to a transition to drier conditions after 15 ka.