bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simple model of shock-wave attenuation in snow
Authors: Johnson Jerome B. 
Published: September 2017

AbstractA simple momentum model, assuming that snow compacts along a prescribed pressure–density curve, is used to calculate the pressure attenuation of shock waves in snow. Four shock-loading situations are examined: instantaneously applied pressure impulses for one-dimensional, cylindrical and spherical shock-wave geometries, and a one-dimensional pressure impulse of finite duration. Calculations show that for an instantaneously applied impulse the pressure attenuation for one-dimensional, cylindrical and spherical shock waves is determined by the pressure density (P–ρ) compaction curve of snow. The maximum attenuation for a one-dimensional shock wave is proportional to (Xf–X0)−1.5 for the multi-stage (P–ρ) curve and (Xf–X0)−2 when compaction occurs in a single step (single-stage compaction), where (Xf–X0) is the shock-wave propagation distance. Cylindrical waves have a maximum attenutation that varies from (R–R0)−2 for single-stage compaction and (R–R0)−1.5 for multi-stage compaction, when (R – R0) ≪ R0, where R is the propagation radius and R0 is the interior radius over which a pressure impulse is applied, to R−4 when (R – R0) ≫ R0 Spherical waves have a maximum attenuation that varies from (R – R0)−2 for single-stage compaction and (R – R0)−1.5 for multi-stage compaction to R−6 when 〈R – R0〉 ≫ R0.The shock-wave pressure in snow for a finite-duration pressure impulse is determined by the pressure impulse versus time profile during the time interval of the impulse. After the pressure impulse ends, shock-wave pressure attenuation is the same as for an instantaneously applied pressure impulse containing the same total momentum. Pressure attenuation near a shock-wave source, where the duration of the shock wave is relatively short, is greater than for a shock wave farther from a source where the shock wave has a relatively long duration. Shock-wave attenuation in snow can be delayed or reduced by increasing the duration of a finite-duration pressure impulse. A sufficiently long-duration impulse may result in no shock-wave pressure attenuation in a shallow snow cover.
The Reconstruction of Former Ice Sheets and their Mass Balance Characteristics using a Non-Linearly Viscous Flow Model
Authors: Boulton G. S. , Smith G. D. , Morland L. W. 
Published: September 2017

AbstractA model of a non-linearly viscous ice sheet is used to investigate the influence of net mass-balance pattern, basal boundary condition, and subglacial topography on the size and shape of ice sheets. The aim is to enable geological evidence of the extent of former ice sheets to be used as indicators of palaeoclimate. A series of curves are presented showing the relationships between ice-sheet span, net mass balance, and equilibrium-line altitude (ELA) for zero and complete isostatic compensation. These are applicable to a very wide range of basal boundary conditions. The way in which they can be used to reconstruct net mass-balance gradients for former ice sheets is demonstrated. Changes in the basal boundary condition only have a strong influence on glacier span when they occur in the terminal zone. Ice-sheet expansion and contraction is not merely accompanied by changes in snow-line elevation, but also by changes in the net mass-balance gradient. The combinations of these required to cause ice-sheet expansion and contraction are analysed. A non-linearly viscous model for ice suggests that ice-sheet volume changes may not be a simple function of their change in areal extent.
Relationships Between Synoptic-Scale Atmospheric Circulation and Glacier Mass Balance in South-Western Canada During the International Hydrological Decade, 1965–74
Authors: Yarnal Brent 
Published: September 2017

AbstractThe relationship between synoptic-scale atmospheric circulation and glacier mass balance in the Cordillera of south-western Canada is investigated. Objective synoptic typing techniques are applied to glaciometeorological data from Peyto Glacier, Alberta, and Sentinel Glacier, British Columbia, and to climatological data from nearby weather stations. Two scales of 500 mbar synoptic weather maps are analyzed and compared. One is smaller with high-wavenumber patterns, the other is larger with more general patterns.The results demonstrate that the mass balance of Peyto and Sentinel Glaciers are related to the 500 mbar patterns. Synoptic types with cyclonic curvature favor glacier accumulation, while anticyclonic types inhibit build-up of the regional snow-pack. Ablation is suppressed by synoptic types associated with cloudy days and/or low temperatures, and is enhanced by types associated with warm, sunny days. Furthermore, findings suggest that both the accumulation and ablation of Sentinel Glacier are controlled by small-scale, high-wavenumber synoptic patterns. Conversely, Peyto Glacier accumulation is more closely associated with large-scale patterns, suggesting that high-frequency mid-tropospheric oscillations embedded within the slow-moving baroclinic zones associated with long-wave disturbances may be dampened by the rough topography of the Canadian Cordillera. Ablation is predicted poorly by both scales at Peyto.
Interaction of Stokes’ Edge Waves with Near-Shore Ice Formation
Authors: Shaw Richard P. , Rumer Ralph R. 
Published: September 2017

AbstractThe interaction of Stokes’ edge waves with a developing near-shore ice zone is examined from two points of view. First, the effect of a well-fragmented ice suspension on the classical Stokes’ edge wave is discussed. Secondly, the possibility that ice-cusp formation (and, thereafter, ice mounds or volcanoes) can be initiated by edge waves is examined. Results indicate a negligible effect of a well-fragmented floating ice field on the Stokes’ dispersion equation for typical wave periods, but do indicate that the presence of a standing Stokes’ edge wave may lead to the initiation of ice-field cusps as ice formation occurs in the near-shore zone.
Snow Stability Index
Authors: Conway H. , Abrahamson J. 
Published: September 2017

AbstractField tests have been developed to measure the shear and tensile strengths of large volumes of snow. Basal shear strengths were measured across and down some slabs of snow, giving highly variable strengths. These measurements support the idea that the basal region of an avalanche may contain zones where the basal shear strength exceeded the gravitational shear stress (i.e. pinning areas) with weak zones between (deficit areas) where the shear strength was less than the gravitational shear stress. The slab tensile stresses induced by these deficit areas would become high if either the deficit length (down-slope) was large, or the deficit itself was large. Measurements of tensile strengths of slabs above weak layers, together with the down-slope gravitational stress of a snow slab, suggest that deficit lengths of only several metres are often sufficient to cause a local tensile failure. In some cases, this local failure may propagate across the remainder of the slope (depending on the pinning distribution) and cause an avalanche. We propose that themaximumlocal deficit, rather than the mean slope deficit of basal shear stress, and themaximumlength of the local deficit, are the first important parameters to consider when evaluating slope stability in the field, since the magnitude of these factors determine the probability of a local tensile failure.
Glacier Sliding at Subfreezing Temperatures
Authors: Shreve R. L. 
Published: September 2017

AbstractNye’s theory of glacier sliding, when modified to incorporate Gilpin’s model of the liquid layer adjacent to foreign solids in ice, predicts non-zero sliding speeds at subfreezing temperatures. Although the predicted speeds are too small to affect glacier motion or even to be observed readily, the total distance of sliding of large glaciers should be adequate to produce bedrock striations. Dissolved solutes in the liquid layer increase the sliding speeds slightly. At temperatures below about – 1° C, 90% of the drag comes from the part of the bed-roughness spectrum at wavelengths between 0.2 and 20 mm regardless of solute concentration. If no more basal ice melts than refreezes (as in a cold glacier), the average liquid-layer thickness and, concomitantly, the sliding speed for given drag and roughness are governed by the ambient temperature. With net melting (as in a temperate glacier), on the other hand, they are governed by the rate of escape of the excess water and no conflict arises between the thickness requirement for run-off water flow and that for regelation water flow. Thus, the proper distinction is not between temperate and cold, but between net melting and no net melting. The theory applies to both cases.
An Index of Regional Snow-Pack Stability based on Natural Slab Avalanches
Authors: Judson Arthur , King Rudy M. 
Published: September 2017

AbstractAn index of regional snow-pack stability based on occurrences of natural slab avalanches was developed using a statistical distribution and a sequential testing procedure. The study interprets avalanche information on 185 paths in the Colorado Front Range. Results show general agreement with operational hazard estimates; test results have real-time evaluation potential.
Determination of the Flow Properties at Dye 3, South Greenland, by Bore-Hole-Tilting Measurements and Perturbation Modelling
Authors: Dahl-Jensen Dorthe 
Published: September 2017

AbstractThe ice-flow properties at great depths have a strong impact on the depth–age relationship of the strata in the Greenland ice sheet. Previous attempts to calculate this relationship have used Glen′s flow law with a temperature-dependent flow-law parameter. The data from the bore-hole-tilting at Dye 3, south Greenland, make it possible to calculate the flow-law parameter versus depth. The flow-law parameter shows a big change at the Holocene/Pleistocene transition with a mean flow enhancement factor of 3 for the ice deposited during the last glaciation. This high enhancement factor is believed to be due to high concentrations of dust and other impurities and small ice-crystal size in the Pleistocene ice. The derived flow-law parameter and the up-stream basal topography are used in a two-dimensional, multi-layer, first-order perturbation model to calculate the surface undulations and strain-rates. The results compare favourably with the observations. The results depend strongly on the flow-law parameter profile, which can therefore be estimated in other areas by perturbation-model calculations along flow lines, if the surface and base topographies are known.
Bedrock Control on Glacial Limits: Examples from the Ladakh and Zanskar Ranges, North-Western Himalaya, India
Authors: Burbank Douglas W. , Fort Monique B. 
Published: September 2017

AbstractIn the north-western Himalaya, the distribution of modem glaciers and snowlines in the Ladakh and Zanskar Ranges adjacent to the Indus River valley suggests comparable climatic conditions prevail in the two ranges. Similarly, the positions of terminal moraines and reconstructed equilibrium-line altitudes (ELAs) indicate equivalent magnitudes of Neoglacial and Late Glacial advances in both ranges. However, the terminal positions and reconstructed ELAs from the late Pleistocene maximum advances are at least 400 m lower in the Ladakh Range than in the nearby Zanskar Range. These differences do not appear to reflect either climatic or tectonic controls. Rather, they are caused by an unusual bedrock configuration in the Zanskar Range, where vertical strata of indurated sandstones and conglomerates, and narrow steep-walled canyons cut through them, created a bulwark that effectively precluded significant down-valley advance. Without recognition of this physical impedance to glacial advance, uncritical reconstructions would greatly overestimate the altitude of the ELA in the Zanskar Range.
The Internal Structure and Ice Crystallography of Seasonal Frost Mounds
Authors: Pollard W. H. , French H. M. 
Published: September 2017

AbstractThe crystal character of the ice core within frost blisters supports the hypothesis that groundwater injection into residual zones of the active layer followed by rapid freezing is the primary growth mechanism for these features. The ice core is characterized by an upper zone of relatively small randomly arranged equigranular ice crystals which change with increasing depth to columnar anhedral crystals, commonly exceeding 200 mm in length, and with crystal diameters ranging between 25 and 35 mm. Petrofabric analyses show that the c-axis orientations are normal to crystal elongations, with crystal growth along the basal plane in an a-axis direction. These observations eliminate ice segregation as a possible growth mechanism, thereby distinguishing seasonal frost mounds from palsas.
The Diurnal Hysteresis of Snow Albedo
Authors: Mcguffie K. , Henderson-Sellers A. 
Published: September 2017

AbstractThe appearance of a diurnal hysteresis in snow albedo is a widely reported phenomenon. This note discusses the relative importance of two separate effects: surface morphosis and surface irregularities (sastrugi). It is concluded that surface morphosis is the more important effect of the two in the region of the marginal cryosphere. Surface irregularities probably are the dominant influence only on permanent cryospheric areas such as the Greenland and Antarctic plateaux.
Sub-Temperate Basal Sliding
Authors: Fowler A. C. 
Published: September 2017

AbstractRecent observations of glacier sliding at temperatures below the melting point are discussed. It is pointed out that these observations can be simply explained by including solid friction in the sliding law. Furthermore, we re-emphasize the point that such sub-temperate sliding has an important effect on the basal boundary conditions which should be applied in model studies of ice sheets and glaciers.
Interpretation of Radio Echoes from Storglaciären, Northern Sweden
Authors: Walford M. E. R. , Kennett M. I. , Holmlund P. 
Published: September 2017

AbstractStorglaciären (lat. 67.5° N., long. 17.5° E.) is a sub-polar glacier which has been the object of detailed study for many years. It responds in a sensitive way to annual and long-term changes in climate but it does not surge. Conditions at the bed and the distribution of englacial water are of considerable interest. In this paper we discuss an attempt to learn something about these matters by radio-echo soundings at metric and decametric wavelengths. We analyse radio-echo records mainly using a scalar-wave theory of the diffraction of pulses. The pulse shapes of echoes are useful because they help us to recognize the types of target and processes responsible for the echoes. We then use simple statistical measurements of radio echoes to provide estimates of certain average properties of the targets. We estimate, for example, the roughness of the glacier bed and the distribution and orientations of scatterers within the ice.
On the Sea-Ice Regime of the Ross Sea, Antarctica
Authors: Sturman Andrew P. , Anderson Mark R. 
Published: September 2017

AbstractA study is made of the sea-ice regime of the Ross Sea, Antarctica, using ESMR passive microwave data and supporting information. Inferences are made of the processes responsible for observed spatial and temporal sea-ice variations. Air flow appears to have a dominant influence on sea-ice distribution and movement, with oceanic circulation playing a more minor role. This is particularly so with coastal polynya development, where katabatic winds are important. It has been possible to identify broad areas of ice convergence and divergence by assimilating the rather limited oceanic and atmospheric information with observed sea-ice variations. In spite of some basic physical similarities of the Weddell and Ross Seas, it is apparent that the major differences in their sea-ice regimes are due to the differing roles of oceanic and atmospheric circulation in each area. The Antarctic Peninsula plays a key role in these differences. Suggestions for further research are also considered.
Melt-Water Drainage Pattern of Composite Glaciers
Authors: Thome Karl N. 
Published: September 2017

AbstractMedial moraines and lineations on the surface of composite glaciers enable the detection of structural and hydrological features. A study of the composite glacier Breidamerkurjökull, south Iceland, indicates relationships between subglacial waterways, ice structure in the junction area, and development of the glacier terminus. First, rivers are situated in or near medial moraines because melt water percolates to the bed and moves from there with the subglacial rivers mainly in the direction of ice flow. Secondly, the contact between two feeder glaciers sometimes forms an angle at the glacier terminus. Then the meltwater river escaping from the contact, generally in a radial direction (away from the glacier front), during the retreat will be transferred to the front of the first receding glacier. The drainage of the contact zone then changes from a radial to a tangential direction, destroying the terminal moraines of the recession stages.Similar relations are found in relics of Pleistocene ice sheets, two examples of which are compared. The huge subglacial channel of the Münsterländer Kiessandzug-Esker below the ice sheet of the Saalian glaciation in the Münsterland, north-west Germany, was formed in the ice-flow direction. It therefore gives details of the morphology and of the great ice-dammed lake east of the Teutoburger Wald ridge. At the contact between the Norwegian and Baltic Sea glaciers, the terminus formed an angle during the maximum extent of the Weichselian glaciation in northern Jutland. During retreat, the Norwegian glacier receded first. The large melt-water river escaping from the contact between both glaciers had formed the huge Karup Sandur during the maximum, but now, during the recession, it changed to the front of the Norwegian ice, destroying the recession moraines there.
Holocene paleoenvironmental reconstruction from deep ground temperatures: a comparison with paleoclimate derived from the δ18O record in an ice core from the agassiz Ice Cap, Canadian Arctic Archipelago
Authors: Taylor Alan E. 
Published: September 2017

AbstractChanges in ground-surface temperature for the past few hundred years have been derived from deep temperature profiles at three wells in the northeastern Canadian Arctic Archipelago, and compared with the climatic history derived from the oxygen-isotope ratio 18O/16O measured in an ice core from the Agassiz Ice Cap, about 180-260 km to the east. Analysis of the ground-temperature profiles suggests that surface temperatures in the area decreased after the Little Climatic Optimum about 1000 years ago until the Little Ice Age (LIA). About 100 years ago, ground-surface temperatures appear to have increased by 2-5K to reach today’s values, while air temperatures increased by 2-3K, according to the isotope record. Part of the larger ground-surface temperature change may be due to other paleoenvironmental effects, such as an increase in snow cover coincident with the end of the LIA.The δ18O climatic record was successful in predicting the general features of the ground-temperature profiles observed at two of the sites, but not the third. There is contemporary evidence that surface temperatures at the latter site may be substantially modified by other environmental factors such as snow cover.
The thermal response of downhill skis
Authors: Colbeck S. C. , Warren G. C. 
Published: September 2017

AbstractThe temperatures in downhill skies were measured with thermocouples to investigate the heat generation associated with the sliding of skis on snow. In these tests we investigated the effects on ski temperature of the ambient snow temperature, snow type, speed, load and thermal conductivity. A significant temperature rise at the base of the ski was found at the onset of motion in all runs. The temperature rise increased for heavier loads and at lower ambient temperatures. Some ski runs lasted long enough to observe a steady-state temperature at the ski base; it increased with ambient temperature. Longitudinal and transverse temperature variations occurred and were sensitive to snow hardness and skiing technique.We also investigated heat flow through the cross-section of the ski with a finite-element model to determine the effects of ski structure on heat retention at the base. We found that the thermal characteristics as determined by the structure of the ski had a significant effect on the temperature at the ski base. At lower temperatures we expect that friction will be greater in skis which have a large aluminum plate across their base. Steel edges have a lesser effect.
Laboratory experiments on the dynamics of powder-snow avalanches in the run-out zone
Authors: Hermann Felix , Hutter Kolumban 
Published: September 2017

AbstractWe report on laboratory experiments on the motion of powder-snow avalanches along a bent chute. The avalanches are simulated as turbulent boundary-layer flows of polystyrene particles in still water along a chute consisting of a straight inclined part, a curved part and a second, possibly inclined, run-out zone. An ultrasonic measuring technique is used to determine mean particle speeds (via the Doppler shift of the reflected signal) and the particle concentration (via the attenuation of the echoes). By ensemble averaging, individual turbulence effects are eliminated. As measuring procedures, profiles were determined for particle velocity and density across the boundary layer; these were taken (i) for the avalanche tail along the entire track, i.e. in the steep part and the run-out zone, and (ii) for the avalanche head in the run-out zone below the kink in the terrain. Moreover, time sections of velocity and density (i.e. time series at fixed positions along a line through the boundary layer) were recorded and the particle mass deposited in the various zones of the track was measured.The analysis of the data reveals the following results: a concave change in the terrain topography acts as a very efficient mechanism for particle sedimentation, thus affecting particle concentration and velocity, and considerable reduction close to the ground, whereas the density is reduced throughout the depth, thus leading to a considerable reduction of dynamic pressure close to the ground and leaving it somewhat greater at higher altitudes. We conclude with practical considerations for the field glaciologist.
Lateral Moraines of Glacier De Tsidjiore Nouve: Form, Development, and Implications
Authors: Small R. J. 
Published: September 2017

AbstractThe relationship between supraglacial lateral moraines and lateral dump moraines at Arolla. Switzerland, is discussed. A detailed study of the lateral moraines of glacier de Tsidjiore Nouve reveals their complex form (as superimposed and nested ridges) and the current mode of development (possibly related to the passage of a kinematic wave). Sedimentological analysis indicates that much of the constituent debris is of supraglacial origin; it is transported either directly from the base of slopes flanking the Pigne d’Arolla ice-fall or via englacial septa comprising marginal sediment incorporated in the accumulation zone. A calculation of the volume of debris in the lateral moraines suggests that glacier de Tsidjiore Nouve has recently been more active in transporting and depositing supraglacial debris than in glacial erosion sensu stricto.