bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow separation and diurnal variability in the hydrology of Conness Glacier, Sierra Nevada, California, U.S.A.
Authors: Lecce Scott A. 
Published: September 2017

AbstractA mass-balance approach using hourly discharge and electrical conductivity values measured over a 10 d period during the ablation season was used to separate englacial and subglacial components of the total meltwater discharge from a small alpine glacier in the Sierra Nevada, California, U.S.A. Symmetrical diurnal hydrographs indicate that little delay occurred as water was tranferred through the drainage system. Electrical conductivity (which varied inversely with proglacial discharge) increased abruptly at each daily conductivity maximum, and cross-correlation analysis indicated that subglacial discharge peaked on the rising limb of the englacial hydrograph (about 2 h prior to the englacial peak). This suggests that a translatory flow process operates in which increased water pressure in the englacial system on the rising limb of the diurnal-discharge cycle forced subglacial water from beneath the glacier in advance of short residence-time meltwater. Net radiation dominated the energy balance at the glacier surface, explaining 86% of the variance in proglacial discharge, which was dominated by the englacial flow component.
Firn-core study from the southern Patagonia ice cap, South America
Authors: Aristarain Alberto J. , Delmas Robert J. 
Published: September 2017

AbstractA shallow firn core, recovered from the southern Patagonia ice cap (elevation 2680 m a.s.I.), has been analyzed for H stable isotope composition and for major soluble chemical compounds. The temperature measurement at 13.17 m depth (bottom of the core) shows that the ice cap is temperate. The chemical profiles indicate that some soluble impurities have been partly washed out by percolation, but seasonal deuterium content variations are relatively well preserved down to the bottom of the core, which allows the net accumulation rate of the site to be calculated (1.2 m water equivalent). The mean concentrations measured in the most recent year recorded (Cl−:4.85, nssSO42−: 0.65, NO3−:0.32, Na+:4.30, K+:0.64 and NH4+: 0.77, in μeq. 1−1) serve as a reference for the background chemical composition of precipitation at mid-southern latitudes under South Pacific meteorological conditions.
Relating the occurrence of crevasses to surface strain rates
Authors: Vaughan David G. 
Published: September 2017

AbstractThe presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met. Understanding how crevasses form will provide information about the stress and strain-rate fields in the ice. This study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses. A literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded. By plotting strain rates (converted to stresses using a creep law) using axes representing the surface-parallel principal stresses, failure envelopes were derived by enclosing measurements where surface crevassing was absent. The derived failure envelopes were found to conform well to theoretical ones predicted by the Coulomb and the maximum octahedral shear stress (von Mises) theories of failure. The derived failure envelopes were scaled by the tensile strength, which was found to vary from 90 to 320 kPa. There was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses. The observed variation in tensile strength could result from variations in ice properties (e.g. crystal size, impurity content or density) or could be related to uncertainty in the constitutive relation. Creep flow and fracture share a very similar temperature dependence, suggesting similar crystal-scale processes are responsible for both. The observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery. The study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large Antarctic ice shelves such as the Filchner–Ronne or Ross Ice Shelves.
Debris entrainment at the ice-bedrock interface in sub-freezing temperature conditions (Terre Adélie, Antarctica)
Authors: Tison J. -L , Petit J. -R. , Barnola J. -M. , Mahaney W. C. 
Published: September 2017

AbstractThe debris-rich ice from the bottom 6 m of the 82 m deep CAROLINE (Coastal Antarctic Record of Last Interglacial Natural Environment) ice core reaching bedrock, and from five 2 m long surface cores at Moraine Prudhomme in Terre Adélie (Antarctica) is described and compared to debris-laden ice from the core-drilling site DIO. Isotopic, total-gas content, CO2 concentration and SEM investigations of embedded particles, together with ice textures and fabrics, rule out “pressure-melting” regelation around bed obstacles or “freezing-on” as possible mechanisms for the debris entrainment at the ice-bedrock interface. It is suggested that the debris entrapment by purely mechanical means (e.g. shearing) is an efficient process in forming basal ice layers (BIL) at sub-freezing temperatures. This process might be dominant at the margin of the Antarctic ice sheet where no ice shelf exists and where a ramp terminus or a buttressing coastal relief induces compressive flow.
Characteristics of avalanching: Kootenay Pass, British Columbia, Canada
Authors: McClung D. M. , Tweedy John 
Published: September 2017

AbstractIndividual variables found to be significant from a correlation analysis are analyzed as a function of probability of avalanching for data from Kootenay Pass, British Columbia. The analysis is compared with a similar study for data from Alta, Utah, U.S.A. The results show that the variable significance is very similar for the two areas. Primary variables include: snowfall rate, weight of new snow, water equivalent of new precipitation, total storm snow and new snow depth. Secondary variables include wind speed and direction, and new-snow density.
Micro-earthquakes beneath Ice Streams Β and C, West Antarctica: observations and implications
Authors: Anandakrishnan S. , Bentley C. R. 
Published: September 2017

AbstractMicro-earthquakes have been monitored at two locations on Ice Stream Β and one on Ice Stream C using a seismographic array built specifically for that purpose. Subglacial micro-earthquakes arc 20 times more abundant beneath Ice Stream C than beneath Ice Stream B, despite the 100 times more rapid movement of Ice Stream B. Triangulation shows the foci beneath Ice Stream C, like those beneath Ice Stream B, to be within a few meters of the base of the ice, presumably within the uppermost part of the bed, and fault-plane analysis indicates slips on horizontal planes at about a 30° angle to the presumed direction of formerly active flow. Source parameters, computed from spectra of the arrivals, confirmed that the speed of slip is three orders of magnitude faster beneath Ice Stream C than beneath Ice Stream Β which means that a five orders-of-magnitude greater fraction of the velocity of Ice Stream C is contributed by the faulting, although that fraction is still small. We attribute the difference in activity beneath the two ice streams to the loss of dilatancy in the till beneath Ice Stream C in the process that led to its stagnation.
The detailed net mass balance of the Ice plain on Ice Stream B, Antarctica: a geographic information system approach
Authors: Bindschadler Robert , Vornberger Patricia L. , Shabtaie Sion 
Published: September 2017

AbstractField data of ice thickness, velocity and accumulation of the ice plain region of Ice Stream B, Antarctica, are organized into a geographic information system (GIS) and used to calculate the spatial pattern of net mass balance. Overall, the ice plain is thickening at a rate of 0.13 ± 0.05 m a−1. Large uncertainties of the high-resolution calculations are reduced by spatial averaging, revealing a number of areas significantly out of balance. Ice in the broad diverging flow field is mostly thinning but a thinner region of the ice plain which includes ice raft “a” is thickening. Thickening is also indicated farther downstream on the ice plain, matching the thickening already calculated to be occurring upstream of Crary Ice Rise. The patterns of net mass balance for the two major tributaries of Ice Stream Β are asymmetric, demonstrating a real difference in the current dynamics of these two tributaries.
New and improved determinations of velocity of Ice Streams B and C, West Antarctica
Authors: Whillans I. M. , Van Der Veen C.J. 
Published: September 2017

AbstractMeasurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.
Siple Coast Project research of Crary Ice Rise and the mouths of Ice Streams B and C, West Antarctica: review and new perspectives
Authors: Bindschadler Robert 
Published: September 2017

AbstractSatellite imagery is used as a basis to review and critique the results of studies at the mouths of Ice Streams Β and C and Crary Ice Rise. In many cases, these past analyses are extended by taking advantage of the broad coverage within each image. New perspectives are provided by the image data and some longstanding controversies are resolved. The grounding line is easily delineated and mapped in areas covered by imagery. Extensive areas of grounded ice with complex patterns of flow stripes are identified on the flanks of Crary Ice Rise. The imagery also allows a corrected map of surface topography in the vicinity of the Downstream Β camp. New questions are posed by hitherto unseen features. Data from the IGY traverse of the Ross Ice Shelf in 1957 are included to demonstrate that large changes have occurred in the past almost 30 years in the area upstream of Crary Ice Rise. These changes include modifications in the surface topography, elimination of crevasses and increases in the ice thickness by approximately 60 m.
Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses
Authors: Retzlaff Rory , Bentley Charles R. 
Published: September 2017

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.
The interaction between an ice sheet and its atmospheric boundary layer
Authors: Hall Alison , Weston Keith 
Published: September 2017

AbstractThe importance of the atmospheric boundary layer for the coupling between the climate and an ice sheet is investigated using a slab model of the atmospheric boundary layer. The model is shown to give reasonable agreement with observations over Antarctica and it is used to look at the effect of different ice-sheet shapes on the boundary layer. The importance of entrainment in bringing heat to the surface is highlighted and is shown to be particularly significant when the ice profile becomes steeper. The model could be used as part of an energy-balance model of snow in order to incorporate the interplay of the boundary layer and ice-sheet shape in the ablation process. The slab model could also be used in a GCM as a parameterization of these sub-grid scale processes which are at present ignored in models on a global scale.
Snow stability during rain
Authors: Conway H. , Raymond C. F. 
Published: September 2017

AbstractThe mechanical response of snowpacks to penetrating liquid water was observed over two winter seasons in the central Cascade Mountains, Washington, U.S.A. Following the onset of rain, three evolutionary regimes of snow behavior were identified: immediate avalanching, delayed avalanching, and return to stability. Immediate avalanching occurred within minutes to an hour after the onset of rain and the time of release could be predicted with an accuracy of less than an hour from meteorological forecasts of the transition from snow to rain. These avalanches usually slid on surfaces substantially deeper than the level to which water or associated thermal effects had penetrated. The mechanism by which alteration of a thin skin of surface snow can cause deep slab failure has not been identified, but several possibilities involving a redistribution of stress are discussed. Delayed avalanches released several hours after rain started. The delay varied, depending on the rate of increasing stress associated with the additional precipitation, and on the time taken for water to penetrate and weaken a potential sliding layer. It is difficult to define accurately the evolving distribution of liquid water in snow which makes it difficult to predict accurately the time of avalanching. Depth profiles of the rate of snow settlement showed that a wave of increased strain rate propagated into the snow in response to penetrating water. This type of measurement could prove useful for predicting when snow stability is reaching a critical condition. Avalanche activity was rare after continuation of rain for 15 h or more. This return to stability occurred after drainage structures had evolved and penetrated the full depth of the snowpack. Established drain channels route water away from potential sliding surfaces and are also relatively strong structures within a snowpack.
Rutschblock precision, technique variations and limitations
Authors: Jamieson J. B. , Johnston C. D. 
Published: September 2017

AbstractThe Swiss rutschblock test provides practical information about the stability of snow slabs. However, its use by avalanche workers and ski guides is limited by the time required to perform the test and recommended minimum slope inclination (30°). The present study shows how time requirements can be reduced by cutting rutschblocks with cords or specialized saws — faster techniques that do not appear to affect the results. Comparing the rutschblock results with a stability index developed in Switzerland shows that the recommended minimum slope inclination can be reduced to 20°, provided a second person is present to observe the small block displacements associated with slope inclinations below 30°. Sets of rutschblocks on slopes that vary in inclination by 8° or more are used to determine the effect of slope inclination on rutschblock scores. Also, the frequency distributions of six large sets of repeated tests are used to estimate the precision of one or two tests on a uniform slope.
Snow Forces
Authors: Salm Bruno 
Published: September 2017

AbstractSnow forces are understood as forces originating from a very slow motion of the seasonal snow cover and acting on boundaries confining it. They depend on the total water-equivalent (a statistical magnitude with a certain probability of occurrence) and on mechanical characteristics of snow. The approximation of considering of snow as a Newtonian liquid fits the requirements for applications best. In this the only mechanical characteristics to be taken into account, besides density, are shear viscosity and Poisson’s ratio. They depend strongly on the snow structure. Generalizations are shown in which the snow cover is subdivided into layers having constant (Newtonian) properties. Non-Newtonian behaviour is also mentioned.
Approximate Solutions for the Interruption of Creep and Glide by Avalanche Defenses
Authors: Evans R. J. , Langdon J. A. 
Published: September 2017

AbstractThis paper presents a numerical calculation procedure for the stress and deformation analysis of a snow mass which is creeping and gliding on an inclined surface and which may, in addition, be restrained by rigid obstacles. The analysis is based on the assumption that the velocity profile at any position in the snow-pack is linear, that is, that sections initially plane remain plane during deformation. Such motion has been observed to occur in the neutral zone and is certainly true at a rigid barrier; accordingly, it appears to be reasonable to restrict the velocity field to be plane everywhere. A constitutive law for steady creep is used which is consistent with the observed neutral zone motion. The solution procedure is illustrated by its application to some problems of avalanche defense barriers. The cases investigated include: continuous barriers, cylindrical barriers, and barriers of finite width. Barrier forces and the extent of back-pressure zones are given.
Propagation of a Plastic Wave in Snow
Authors: Wakahama Gorow , Sato Atsushi 
Published: September 2017

AbstractWhen snow is pushed very fast by a moving body a plastic wave is generated at the head of the body. If the velocity of the moving body becomes close to that of the plastic wave, the snow may exert a great resistive force against the body as predicted by Yosida. It is, therefore, very important to study the dynamic behaviour of snow at a high rate of deformation, such as takes place when a snow plough is used on the highway, a train runs on a railroad covered with snow, or an avalanche occurs. Hence, this study is concerned with the safety and maintenance of winter traffic and transportation, and also with the generation and propagation of an avalanche. In order to clarify the detailed processes of the deformation of snow at high rates, laboratory experiments were made by compressing snow at high speed. The propagation of a plastic wave through snow was observed by using a high-speed camera and a pressure-detecting device. Analyses of the data obtained gave the velocity of the plastic wave for various kinds of snow whose density ranged from 0.17 to 0.46 Mg m-3 and free-water content from o to 17%, whereby studies were made into the dependences on the density and free-water content of the velocity of the plastic wave. When the impact velocity was 4.3 ± 0.2 m s-1, the wave velocity ranged from 5 m s-1 for a new snow to 12 m s-1 for a fine-grained, well-settled snow. The plastic-wave velocity in wet snow was, in general, smaller than that in dry snow of the same density. Changes in density and structure of snow associated with the passage of a plastic wave were studied and discussed. The pressure at the wave front was measured; values of 0.1-0.3 bar were obtained, these are of the same order as the value estimated from theoretical formulae. The plastic-wave velocity was also observed for a confined snow, which showed a larger velocity and plastic strain than an unconfined snow.
Expected Snow Loads on Structures from Incomplete Hydrological Data
Authors: Martinec J. 
Published: September 2017

AbstractAn assessment of snow loads in Switzerland was required for a revision of the building code. Settling curves of snow are used to compute water equivalents of snow if direct measurements are not available. Based on a frequency analysis, relations between the snow load and the altitude are given for various return periods. Problems of regional effects and of converting the snow-cover data to roof loads are outlined.
Measuring the Uniaxial Compressive Strength of Ice
Authors: Haynes F. D. , Mellor M. 
Published: September 2017

AbstractAn attempt was made to develop a simple but accurate method for making compressive strength tests on right circular cylinders. Compliant loading platens were designed to apply uniform normal stress without introducing significant interface radial shear stresses. The compliant platens gave reproducible results that agree well with results obtained by a precise conventional technique. Accurate results were obtained with simple specimen preparation, and with short specimens where the length-to-diameter ratio was less than unity. Platens were made from a rubber-like urethane which was molded in aluminum cylinders to provide lateral restraint. Uniaxial compression tests on cylindrical polycrystalline ice specimens were made to determine the characteristics of the platens. For 21 specimens with ends prepared on a lapping plate to obtain a mirror finish, the measured strength showed a variation of only 13% for length-to-diameter ratios from 0.74 to 2.5, with no systematic trend. Another 21 specimens with length-to-diameter ratios of about 2.35 were tested with various platens and various methods of specimen end preparation. The strength for specimens with saw-cut ends and for those with ends lapped showed very little difference when tested with the rubber platens.
Friction of a Steel Ball on a Single Crystal of Ice
Authors: Tusima Katutosi 
Published: September 2017

AbstractThis paper presents the results of a study carried out to explain the low friction on ice. Friction of a steel ball on a single crystal of ice was measured as a function of load, velocity, temperature, and diameter of slider. It was found that even when the velocity was very small (1.5 - 10-7 to 1.8-10–3 m/s) the coefficient of friction was very small ranging from 0.005 to 0.2, although friction on the prismatic plane was twice as large as that on the basal plane. The coefficient of friction increased with load, which means that Amonton’s classical law of friction is not applicable to ice. The coefficient of friction increased with decreasing velocity, which may result from the creep of ice in the contact area. The friction strongly increased as the temperature became close to °C. A minimum friction was observed for a definite temperature. It was found that the explanation of the results obtained is given satisfactorily neither by the classic pressure-melting theory nor by the friction-melting theory, but only by adhesion theory.