Grain‐size distribution of subglacial till and its realtion to glacial scrushing and abrasion

Haldorsen, Sylvi

doi:10.1111/j.1502-3885.1981.tb00472.x

Cited by 175 publications

(79 citation statements)

References 13 publications

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“…Also, they are not the products 395 of two mechanisms. These are in contrast with some earlier works (Rogers et al, 1963, Haldorsen, 1981, 396 Wright, 1995, but in agreement with another line of works (Jefferson et al, 1997, Cheng, 2004, Kumar et 397 al., 2006. This is because of the differences between crystallographically pure quartz and that with 398 internal defects.…”

Section: Discussion 381contrasting

confidence: 57%

Micromechanics of quartz sand breakage in a fractal context

et al. 2014

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19From a Quaternary science perspective, sand-sized quartz as well as silt-sized quartz is often 20 acknowledged as final products of glacial abrasion through different evolution mechanisms. This view 21 challenges the existence of any universal comminution process, which may relate the formation of detrital 22 quartz sand and silt. The contribution of grain size, energy input, and crystalline integrity in the scale of 23 quartz crushability has long been matter of much debate. The present empirical work examines the 24 micromechanics of sand-to-silt size reduction in the quartz material. A series of grinding experiments was 25 performed on Leighton Buzzard Lower Greensand using a high-energy disc mill. Analogous conditions to 26 glacial abrasion are provided due to the combined abrasion between grains' asperity tips, and also 27 between grains and rotating smooth tungsten carbide pestle. Discontinuous breakage approach allowed 28 a control on grains' crystalline defects. To enable an objective assessment of micromechanics of size 29 reduction, measurements of particle and mode size distribution, fractal indexes and micro-morphological 30 signatures were made. The crushing approach was probed through varied grinding time at a constant 31 energy input, as well as varied energy input at constant grinding time. Breakage pathway was inspected 32 via laser diffraction spectroscopy and transmission light microscopy. Results suggested that the grain 33 breakdown is not necessarily an energy-dependent process. Non-crystallographically pure quartz sand 34 and silt are inherently breakable materials through a fractal breakdown process. Results also revealed 35 that the internal defects in quartz are independent from size and energy input. 36

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Section: Discussion 381contrasting

confidence: 57%

Micromechanics of quartz sand breakage in a fractal context

et al. 2014

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“…The relatively small silt-andclay fraction, characteristic of many basal tills (e.g. Haldorsen, 1981;Hooke and Iverson, 1995;Truffer and others, 1999), caused the till's permeability to be high and thereby reduced the likelihood that its dilation or contraction during shear would produce non-hydrostatic pore pressures (e.g. Moore and Iverson, 2002).…”

Section: Till Prism and Instrumentsmentioning

confidence: 99%

Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation

Iverson¹,

Hooyer

Fischer

et al. 2007

J. Glaciol.

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ABSTRACT. To avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m Â Â 1.6 m Â 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7-12 days, the glacier regelated downward into the prism to depths of 50-80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high porewater pressure (70-100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.

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“…The sedimentological characteristics of glaciological landforms can offer valuable insights into their mode of formation and the origin and transport history of the material involved (Boulton, 1978;Eyles and Rogerson, 1978;Haldorsen, 1981;McLaren and Bowles, 1985;Brodzikowski and Van Loon, 1987;Shaw, 1987;Hooke and Iverson, 1995;Knight and others, 2000). Grain-size frequency distribution data describe the relative amount, by mass or volume, of particles according to their size in a sample, and are often combined with observations of clast fabric and descriptions of clast shape to describe the lithofacies under investigation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Sedimentological characterization of Antarctic moraines using UAVs and Structure-from-Motion photogrammetry

et al. 2015

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ABSTRACT. In glacial environments particle-size analysis of moraines provides insights into clast origin, transport history, depositional mechanism and processes of reworking. Traditional methods for grain-size classification are labour-intensive, physically intrusive and are limited to patch-scale (1 m 2 ) observation. We develop emerging, high-resolution ground-and unmanned aerial vehicle-based 'Structure-from-Motion' (UAV-SfM) photogrammetry to recover grain-size information across a moraine surface in the Heritage Range, Antarctica. SfM data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning, and were found to be accurate to within 1.7 and 50 mm for patch-and site-scale modelling, respectively. Grain-size distributions were obtained through digital grain classification, or 'photo-sieving', of patch-scale SfM orthoimagery. Photo-sieved distributions were accurate to <2 mm compared to control distributions derived from dry-sieving. A relationship between patch-scale median grain size and the standard deviation of local surface elevations was applied to a site-scale UAV-SfM model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0.3 km 2 area of moraine. This highly automated workflow for site-scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis.

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Grain‐size distribution of subglacial till and its realtion to glacial scrushing and abrasion

Cited by 175 publications

References 13 publications

Micromechanics of quartz sand breakage in a fractal context

Micromechanics of quartz sand breakage in a fractal context

Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation

Sedimentological characterization of Antarctic moraines using UAVs and Structure-from-Motion photogrammetry

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