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Although rates of fluvial incision across the Colorado Plateau are known reasonably well, rate variability through time and its controlling processes are still poorly understood. We used boulder armored benches from the Teasdale-Torrey lowlands reach of the Fremont River in the northwestern Colorado Plateau (Utah, USA) as temporal markers to determine regional incision rates and explore controls on rate variability. Bench gravels are sourced from Tertiary volcanic rocks capping nearby Boulder and Thousand Lakes Mountains. The sedimentology of bench deposits suggests that most form from mass movement with later fluvial reworking. Volcanic boulders are tougher than the local sedimentary bedrock, which promotes boulder armoring and topographic inversion. Thirty-seven boulder cosmogenic 3He exposure ages from 11 different benches range from >600 ka to ca. 100 ka. Soil carbonate stages from two benches are in good agreement with surface exposure ages. Averaged Fremont River and tributary incision rates determined from bench exposure ages are 32% faster for tributaries off of Thousand Lakes Mountain (0.41 m/k.y.) than tributaries off of Boulder Mountain (0.28 m/k.y.). This difference in incision rate may be due to Laramideage structures limiting incision for the tributaries that drain Boulder Mountain and extensive Pleistocene ice caps on Boulder Mountain creating a wider and thicker boulder armor slowing incision. 

The Pleistocene Epoch was characterized by extensive glacier systems in numerous mountain ranges around the world. Mapping glacial landforms and deposits over many decades of prior work has afforded reconstructions of mountain glaciers, chiefly during the last Pleistocene glaciation and subsequent deglaciation. The availability of high-resolution satellite imagery, digital terrain models, and numerical chronologies of glacial deposits and landforms provides opportunities for mapping paleoglacier outlines and reconstructing ice thickness and volume during specific periods across glaciated regions at different spatial scales. Most paleoglacier reconstructions require outlines corresponding to a specific valley and terminus. However, various formats of digital paleoglacier outlines exist in the literature, some of which encompass entire glacier complexes or ice caps without differentiating between individual valleys and outlet glaciers. Also, unlike inventories of present-day glaciers such as the Randolph Glacier Inventory, digitized paleoglacier outlines lack standardized attributes. In this study, we developed an ArcGIS toolbox to subdivide paleoglacier outlines into individual polygons constrained within watershed boundaries (drainage basins) and to derive a consistent set of attributes related to the geometry, topography, and ice thickness of paleoglaciers. We demonstrate the applications of this toolbox in glaciated mountain areas in Costa Rica, the western U.S., and the central Tibetan Plateau. Although some manual adjustments are still necessary, this toolbox provides an efficient means to standardize the format and derive attributes for paleoglacier outlines. Our proposed framework and newly developed ArcGIS toolbox for standardizing paleoglacier outline formats and attributes improve the value, accuracy, and utility of paleoglacier mapping and paleoclimate reconstruction, and facilitate consistency and comparability among model simulations of glacier and climate changes from the past to present and into the future. 

Constraining the timescales of sediment transport by glacier systems is important for understanding the processes controlling sediment dynamics within glacierized catchments, and because the accumulation of supraglacial sediment influences glacier response to climate change. However, glacial sediment transport can be difficult to observe; sediment can be transported englacially, subglacially, supraglacially or at the ice margins, and may be stored temporarily on headwall slopes or within moraines before being (re‐)entrained and transported by glacier ice. This study is a proof of concept of the use of luminescence rock surface burial dating to establish rates of englacial sediment transport. Our novel approach combines luminescence rock surface burial dating of englacial clasts with an ice‐flow model that includes Lagrangian particle tracking to quantify rates of sediment transport through the Miage Glacier catchment in the Italian Alps. Luminescence rock surface burial ages for seven samples embedded in the near‐surface ice in the ablation area range from 0.0 ± 1.0 to 4.7 ± 0.3 ka and are consistent with the ice‐flow model results. Our results show that the transport durations of individual clasts vary by an order of magnitude, implying rapid clast transport near the glacier surface and longer transport histories for clasts transported lower in the ice column. In some cases, clasts were stored on the headwalls or within ice‐marginal moraines for several thousand years before being englacially transported. The results illustrate the different routes by which glaciers transport sediment and provide the first direct measurements of englacial sediment transport duration.