Bedforms of Thwaites Glacier, West Antarctica: Character and Origin

Alley, Richard B.; Holschuh, Nicholas; MacAyeal, Douglas R.; Parizek, B. R.; Zoet, Lucas K.; Riverman, K. L.; Muto, Atsuhiro; Christianson, Knut; Clyne, Elisabeth; Anandakrishnan, S.; Stevens, N. T.

doi:10.1029/2021jf006339

Cited by 18 publications

(30 citation statements)

References 137 publications

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“…The "double-valued" trend we observe between N and t sb contradicts the common assumption for subglacial settings that Q sed increases monotonically with N. Although the rising limb occurs over a range of N that is particularly relevant to the dynamics of modern ice streams (Meyer et al, 2018), these stresses are substantially lower than pressure concentrations possible on the stoss side of bedform obstacles (Alley et al, 2021), which would fall within the decreasing limb of the relationship. This overall behavior, however, is consistent with the double-valued trend that Kasmalkar et al (2021, Figure 3) reported from recent DEM experiments investigating till dynamics, and it aligns with the inverse relationship between N and t sb reported for numerous physical and numerical experiments within the fields of civil engineering and soft matter physics (Desrues & Viggiani, 2004;Gu et al, 2014, their Figure 10a), since the minimum stresses applied in these studies are generally too high to capture the rising limb we observe at low stresses (N ∼ 0-50 kPa).…”

Section: Double-valued Sediment Flux At Increasing Effective Stresscontrasting

confidence: 79%

“…The “double‐valued” trend we observe between N and t sb contradicts the common assumption for subglacial settings that Q sed increases monotonically with N . Although the rising limb occurs over a range of N that is particularly relevant to the dynamics of modern ice streams (Meyer et al., 2018), these stresses are substantially lower than pressure concentrations possible on the stoss side of bedform obstacles (Alley et al., 2021), which would fall within the decreasing limb of the relationship. This overall behavior, however, is consistent with the double‐valued trend that Kasmalkar et al.…”

Section: Discussionmentioning

confidence: 99%

“…Conversely, the areas of the bed that experience sustained high stresses and fast velocities, such as the stoss side of bedform obstacles, will have elevated Q sed , so long as the driving stress exceeds the shear strength of the till. This should occur even at values of N past the point where shear bands begin to thin, since increased pressure induced on the adverse slope of the feature dewaters the ice‐bed interface (Creyts & Schoof, 2009) and routes water around the bump (Alley et al., 2021). The corresponding reduction in film thickness increases the contact between ice and till on the stoss side, facilitating the transport of sediment near the ice sole down‐glacier at a rate proportional to v ice .…”

Section: Discussionmentioning

confidence: 99%

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Characterizing Sediment Flux of Deforming Glacier Beds

Hansen

Zoet

2022

JGR Earth Surface

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Deformation of subglacial sediment during basal slip shapes the beds of many fast‐flowing glaciers and ice streams. The resultant sediment flux impacts glacier dynamics and rates of subglacial erosion over a range of timescales, but its fundamental dependencies are not well understood. Using a cryogenic ring shear device, we conducted experiments to investigate the effects of both effective stress and slip speed on rates of till transport. Sediment fluxes were computed using digital image correlation from a photographic time series of the till bed. We find a near‐linear relationship between sediment flux and slip speed, but a non‐monotonic, double‐valued dependency of sediment flux on effective stress. Deformation primarily occurred in a thin shear band near the ice sole, the thickness of which could vary with both parameters. Coupling between ice and till increased at higher slip speeds and effective stresses and scaled the magnitude of the flow profile.

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Section: Double-valued Sediment Flux At Increasing Effective Stresscontrasting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Characterizing Sediment Flux of Deforming Glacier Beds

Hansen

Zoet

2022

JGR Earth Surface

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“…We suggest three possible explanations for resolving the discrepancy between observed and theoretical maximum effective-normal-stresses. Firstly, prominent bedrock outcrops could significantly inhibit ice flow, allowing stoss-side effective-normal-stresses of the order of at least 1 𝑀𝑃𝑎 to develop 52 . A second explanation again lies with bedrock outcrops, whereby impermeable bedrock might inhibit the transport of fluids, facilitating dewatered regions.…”

Section: Effective Normal-stress Vs Effective Fluid Pressurementioning

confidence: 99%

Friction and slip measured at the bed of an Antarctic ice stream

Hudson

Kufner

Brisbourne

et al. 2022

Preprint

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The slip of glaciers over the underlying bed is the dominant mechanism governing the migration of ice from land into the oceans, contributing to sea-level rise. Yet glacier slip remains poorly understood or constrained by observations. Here we observe both frictional shear-stress and slip at the bed of an ice stream, using 100,000 repetitive stick-slip icequakes from Rutford Ice Stream, Antarctica. Basal shear-stresses and slip-rates vary from 10^4 to 10^7 Pa and 0.2 to 1.5 m day^(-1), respectively. Friction and slip vary temporally over the order of hours and spatially over 10s of meters, caused by corresponding variations in ice-bed interface material and effective-normal-stress. Our findings also suggest that the bed is substantially more complex than currently assumed in ice stream models and that basal effective-normal-stresses may be significantly higher than previously thought. The observations also provide previously unresolved constraint of the basal boundary conditions of ice dynamics models. This is critical for constraining the primary contribution of ice mass loss in Antarctica, and hence the endeavour to reduce uncertainty in sea-level rise projections.

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“…They propose some of the till to be deposited in the downstream end of the obstacle, while the erosion of sediment possibly exposes bedrock in the moat. Once the moat has reached a certain depth, changes in water routing will drive water into the moat (Alley et al, 2021).…”

Section: Hypothesis Of Moat Formationmentioning

confidence: 99%

Bed properties and three-dimensional topography from radar at Rutford Ice Stream, West Antarctica

Schlegel¹

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Outlet glaciers and ice streams of the Antarctic Ice Sheet provide dis-charge pathways, transporting >90% of the continents ice into the oceans. Elongated landforms beneath fast ﬂowing ice streams form as a result of ice-bed interactions. Understanding their link to ice ﬂow dynamics will better inform subglacial processes and allow these processes to be correctly implemented in predictive numerical ﬂow models, thus improving predictions of future contributions to sea level rise. In this thesis, a section of the bed of Rutford Ice Stream (West Antarctica), containing numerous elongated subglacial landforms, was analysed using a suite of 2D and 3D radar data with repeat surveys. Bed properties vary spatially over a 100 m scale and imply the pat-tern of inferred basal motion in this area is more complex, and basal sliding dominated areas are more extensive, than previously assumed. Local erosion rates are high (1 m/a), indicating a mobile bed, whereas most of the bed shows no temporal change, implying stability of the basal environment. Observations of landforms shortening, and previ-ous observations of landforms extending, highlight that landforms are a non-static part of the bed. Isolated landforms appear to consist of a more rigid sediment at their upstream end with softer sediment down-stream. Some landforms contain a water body (up to 10 km length) along their crest. 3D processed data reveal a so far unseen moat (de-pression) around one landform. Dimensions of the upstream part of the moat are comparable to dimensions of the upstream end of the landform (<50 m height, <300 m width). Observations suggest land-forms are depositional features, while the moat was likely eroded. The radar and other data analysed provide detailed landform and moat ar-chitecture, at a resolution comparable to digital elevation models of deglaciated terrain, and together with interpreted properties give a solid basis for testing existing landform formation theories.

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Bedforms of Thwaites Glacier, West Antarctica: Character and Origin

Cited by 18 publications

References 137 publications

Characterizing Sediment Flux of Deforming Glacier Beds

Characterizing Sediment Flux of Deforming Glacier Beds

Friction and slip measured at the bed of an Antarctic ice stream

Bed properties and three-dimensional topography from radar at Rutford Ice Stream, West Antarctica

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