An official website of the United States government
Abstract Sediment erosion, transport, and deposition by glaciers and ice sheets play crucial roles in shaping landscapes, provide important nutrients to downstream ecosystems, and preserve key indicators of past climate conditions in the geologic record. While previous work has quantified sediment fluxes from subglacial meltwater, we also observe sediment entrained within basal ice, transported by the flow of the glacier itself. However, the formation and evolution of these debris‐rich ice layers remains poorly understood and rarely represented in landscape evolution models. Here, we identify a characteristic sequence of basal ice layers at Mendenhall Glacier, Alaska. We develop a numerical model of frozen fringe and regelation processes that describes the co‐evolution of this sequence and explore the sensitivity of the model to key properties of the subglacial sedimentary system, using the Instructed Glacier Model to parameterize ice dynamics. Then, we run numerical simulations over the spatial extent of Mendenhall Glacier, showing that the sediment transport model can predict the observed basal ice stratigraphy at the glacier's terminus. From the model results, we estimate basal ice layers transport between 23,300 and 39,800 of sediment, mostly entrained in the lowermost ice layers nearest to the bed, maximized by high effective pressures and slow, convergent flow fields. Overall, our results highlight the role of basal sediment entrainment in delivering eroded material to the glacier terminus and indicate that this process should not be ignored in broader models of landscape evolution.
more »
« less
This content will become publicly available on March 1, 2026
Tracking Sediment Transport Through Miage Glacier, Italy, Using a Lagrangian Approach With Luminescence Rock Surface Burial Dating of Englacial Clasts
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.
more »
« less
- Award ID(s):
- 2223354
- PAR ID:
- 10644080
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- Volume:
- 130
- Issue:
- 3
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT Be dating of moraines has greatly improved our ability to constrain the timing of past glaciations and thus past cold events. However, the spread in ages from a single moraine is often greater than would be expected from measurement uncertainty, making paleoclimatic interpretations equivocal. Here we present 28 new10Be ages from ice‐cored Neoglacial moraines on Baffin Island, Arctic Canada, and explore the processes at play in moraine formation and evolution through field observations and a numerical debris‐covered glacier model. The insulating effect of debris cover modifies glacier lengths and results in the development of ice‐cored moraines over multiple advances and thousands of years. Although ice cores can persist for several millennia, spatially variable ice core melt‐out contributes to moraine degradation and boulder destabilization, making it likely that the10Be clock is reset on moraine boulders in these settings. Thus, exposure ages from ice‐cored moraines must be interpreted with caution. The oldest ages, after excluding samples with inheritance, provide the best estimates of initial moraine formation. Three Baffin Island moraines yield10Be ages suggesting formation at 5.2, 4.6 and 3.5 ka, respectively, adding to a growing body of evidence for significant summer cooling millennia before the Little Ice Age.more » « less
-
Abstract Glacier sliding has major environmental consequences, but friction caused by debris in the basal ice of glaciers is seldom considered in sliding models. To include such friction, divergent hypotheses for clast‐bed contact forces require testing. In experiments we rotate an ice ring (outside diameter = 0.9 m), with and without isolated till clasts, over a smooth rock bed. Ice is kept at its pressure‐melting temperature, and meltwater drains along a film at the bed to atmospheric pressure at its edges. The ice pressure or bed‐normal component of ice velocity is controlled, while bed shear stress is measured. Results with debris‐free ice indicate friction coefficients < 0.01. Shear stresses caused by clasts in ice are independent of ice pressure. This independence indicates that with increases in ice pressure the water pressure in cavities observed beneath clasts increases commensurately to allow drainage of cavities into the melt film, leaving clast‐bed contact forces unaffected. Shear stresses, instead, are proportional to bed‐normal ice velocity. Cavities and the absence of regelation ice indicate that, unlike model formulations, regelation past clasts does not control contact forces. Alternatively, heat from the bed melts ice above clasts, creating pressure gradients in adjacent meltwater films that cause contact forces to depend on bed‐normal ice velocity. This model can account for observations if rock friction predicated on Hertzian clast‐bed contacts is assumed. Including debris‐bed friction in glacier sliding models will require coupling the ice velocity field near the bed to contact forces rather than imposing a pressure‐based friction rule.more » « less
-
Abstract The time-evolution of glacier basal motion remains poorly constrained, despite its importance in understanding the response of glaciers to climate warming. Athabasca Glacier provides an ideal site for observing changes in basal motion over long timescales. Studies from the 1960s provide an in situ baseline dataset constraining ice deformation and basal motion. We use two complementary numerical flow models to investigate changes along a well-studied transverse profile and throughout a larger study area. A cross-sectional flow model allows us to calculate transverse englacial velocity fields to simulate modern and historical conditions. We subsequently use a 3-D numerical ice flow model, Icepack, to estimate changes in basal friction by inverting known surface velocities. Our results reproduce observed velocities well using standard values for flow parameters. They show that basal motion declined significantly (30–40%) and this constitutes the majority (50–80%) of the observed decrease in surface velocities. At the same time, basal resistive stress has remained nearly constant and now balances a much larger fraction of the driving stress. The decline in basal motion over multiple decades of climate warming could serve as a stabilizing feedback mechanism, slowing ice transport to lower elevations, and therefore moderating future mass loss rates.more » « less
-
Abstract. To understand the erosivity of the eastern portion of the Laurentide Ice Sheet and the isotopic characteristics of the sediment it transported, we sampled buried sand from deglacial features (eskers and deltas) across eastern Canada (n = 10), a landscape repeatedly covered by the Quebec-Labrador Ice Dome. We measured concentrations of 10Be and 26Al in quartz isolated from the sediment and, after correcting for sub-surface cosmic-ray exposure after Holocene deglaciation, used these results to determine nuclide concentrations at the time the ice sheet deposited the sediment. To determine what percentage of sediment moving through streams and rivers currently draining the field area was derived from incision of thick glacial deposits as opposed to surface erosion, we used 10Be and 26Al as tracers by collecting and analyzing modern river sand sourced from Holocene-exposed landscapes (n = 11). We find that all ten deglacial sediment samples contain measurable concentrations of 10Be and 26Al equivalent on average to several thousand years of surface exposure – after correction, based on sampling depth, for Holocene nuclide production after deposition. Error-weighted averages (1 standard deviation errors) of measured 26Al/10Be ratios for both corrected deglacial (6.1 ± 1.2) and modern sediment samples (6.6 ± 0.5) are slightly lower than the production ratio at high latitudes (7.3 ± 0.3) implying burial and preferential decay of 26Al, the shorter-lived nuclide. However, five deglacial samples collected closer to the center of the former Quebec-Labrador Ice Dome have much lower corrected 26Al/10Be ratios (5.2 ± 0.8) than five samples collected closer to the former ice margins (7.0 ± 0.7). Modern river sand contains on average about 1.75 times the concentration of both nuclides compared to deglacial sediment corrected for Holocene exposure. The ubiquitous presence of 10Be and 26Al in eastern Quebec deglacial sediment is consistent with many older-than-expected exposure ages, reported here and by others, for bedrock outcrops and boulders once covered by the Quebec-Labrador Ice Dome. Together, these data suggest that glacial erosion and sediment transport in eastern Canada were insufficient to remove material containing cosmogenic nuclides produced during prior interglacial periods both from at least some bedrock outcrops and from all glacially transported sediment we sampled. Near the center of the Quebec-Labrador Ice Dome, ratios of 26Al/10Be are below those characteristic of surface production at high latitude. This suggests burial of the glacially transported sediment for at least many hundreds of thousands of years and the possibility that ice at the center of the Quebec-Labrador Ice Dome survived many interglacials when more distal ice melted away.more » « less
