The Role of Reptation in Dune Slipface Dynamics
Bibliographic record
Abstract
Introduction: The sediment dynamics of dune lee slopes has received very little attention when compared with the stoss face. Historically, this interest has focused on the bedding strata or laminations formed through avalanching and grainfall (e.g. [1-3]). However lack of understanding of the process of avalanching, specifically the linkage between the rate of sediment transport over the dune brink with the frequency and magnitude of the event, has hampered the use of laminae in reconstructing dune dynamics from these preserved records. Two 2-D kinematic dune avalanche models have been developed [4,5], although neither have been field tested. Through their development both avalanche models demonstrated the requirement of an accurate predictive description of the spatial distribution of lee slope grainfall settling (S) for use in determining the changing angle of the slipface slope, and thus the moment of avalanche when the slope reaches its angle of initial yield (θi). As the grainfall rate drops off with distance from the crest a “pillow” of sand develops on the upper reach, avalanche initiation will occur when the slope inflection point (the maximum slope of the changing surface) exceeds θi. Figure 1 shows an avalanche which initiated mid-slope, and the length of the scarp receding towards the crest shows the extent of this sand “pillow”. Laboratory, field and modeling studies into the grainfall pattern [5-9] have all relied on direct capture of the falling grains and have not examined the redistribution of the grains through reptation, grains rebounding from the bed yet lacking the energy to be considered saltators [10]. Experiments were conducted to investigate the significance of reptation to the pre-avalanche sediment dynamics on dune slipfaces, and its impact on avalanching. Methods: The experiments were carried out in a Dune Simulation Tunnel (Fig. 1), constructed jointly by the University of Guelph’s Wind Erosion Laboratory, and the Desert Research Institute of Nevada. Located in Harley, Ontario, Canada, this tunnel was designed to simulate a small 1.2 m crest height, aspect ratio 0.08 h/L dune for which field observations existed [9], and contained both lee and stoss slopes with a 1:1 scaling. Measurements of grainfall rates through cup collection, reptation rates with custom reptation traps, and changes in elevation (both through solely grainfall/ reptation, and through grainfall/ reptation/ avalanching) were made using a 3-D laser scanner (Konica-Minolta
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 source (direct Gemma or distilled Codex), 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".