Pressure-dependent viscosity and interfacial instability in coupled ice–sediment flow
Bibliographic record
Abstract
We study an interfacial instability in the coupled flow of ice and subglacial sediment, both modelled as viscous media. Unlike other interfacial instabilities in coupled viscous flows at zero Reynolds number, the mechanism considered here does not rely on buoyancy or the effect of an upper free surface, but on the pressure-dependence of the sediment viscosity. Specifically, the instability relies on sediment rheology being such that, when sediment flows in simple shear, sediment flux increases with compressive normal stress at the ice–sediment interface when the velocity of the interface is kept constant. When ice moves over a shallow bump in the interface, it generates a higher compressive stress on the bump's upstream side than in its lee. If in addition the effective sediment viscosity is low compared with that of ice, interfacial velocity remains approximately constant, and this then implies that more sediment flows into the bump than out of it, causing it to grow. Modelling ice as a Newtonian material, we show that this mechanism works for a wide range of sediment rheologies, including the highly nonlinear shear-thinning ones typically thought most appropriate for the description of ‘nearly plastic’ sediment. The instabilities predicted are essentially two-dimensional, with infinite transverse wavelength, and a nonlinear model shows that growth is unbounded until cavitation occurs in the lee of evolving bumps on the interface. The instability mechanism does not seem to predict the formation of common glacial landforms, but may explain the formation of water-filled cavities on deformable glacier beds.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".