bluuebunny/crossref_metadata_2025_split huggingface dataset:
Informal Cooperative State-Federal Avalanche-Warning System and Public Education Program for South-Central Alaska, U.S.A.
Authors: Hackett Steve W. , Fesler Douglas 
Published: September 2017

AbstractThe sagas of Alaskan winter outdoor activities contain increasing accounts of sudden deaths from snow avalanches. Over 100 documented fatalities have occurred within Alaska since 1898 ; 22 people died in south-central Alaska in the past 8 years. With increases in population, development, and use of the mountainous areas, avalanche warning and public education have acquired a new and very important function in Alaska.Some efforts towards establishing an avalanche warning system for south-central Alaska have been initiated by state and federal agencies. Snow-avalanche education programs presented by Alaska Division of Parks, local rescue groups, and outdoor educators have helped to increase the overall avalanche awareness in the Anchorage community. Formalization and expansion of current efforts are aimed to reduce future snow-avalanche accidents and fatalities.
Preliminary Research on Physical and Mechanical Properties and Avalanche of Seasonal Snow Cover at the Avalanche Station In T'ien-shan, China
Authors: Xiangsong Zhang , Yanlong Wang 
Published: September 2017

AbstractThe mountains of western and central T’ien-shan have extensive snow cover and consequent avalanches, however conditions in this area of central Asia are different from those in many other regions with avalanches. Snow cover is not very thick but it experiences very large temperature gradients which dominate its metamorphism, thus depth hoar forms extensively and becomes the principal snow type, so the density therefore remains low as does mechanical hardness. Avalanching activity and total volume vary enormously from year to year; 1968-69, with 211 avalanches of 147 000 m3, accounts for 53% of the avalanches and 75% of the volume of all the avalanches in the seven years 1967-74 in the area of the Gunes avalanche station. Although they can occur from November to April, the main months are January and March with a minimum in February. A snow depth of 50-60 cm is needed for avalanching. Below —10°C dry-snow avalanches occur, while above about —5°C wet-snow avalanches happen. These are often caused by melt water penetrating rapidly through the extensive depth hoar and initiating full-depth avalanches.
Finite-Element Analysis of Snow on Slopes
Authors: Navarre J. P. , Desrues J. 
Published: September 2017

AbstractThis study describes the application of an incremental rheological law for snow in a finite-element model. The computation simulates the variation of strains and stresses in a layer of snow covering an inclined plane of variable slope. At the same time, a physical simulation was carried out in a cold room to verify the results obtained with the model. This work illustrates the value of a finite-element model for snow, but also the complications attendant on its use. Indeed, the integration of the law may lead to oscillations due to the rate of variation of the stresses, and this means that the time increment must be modulated during the computation.
Radar for Avalanches—Measurement and Warning
Authors: Fritzsche W. 
Published: September 2017

AbstractAutomatic measuring devices can greatly facilitate the difficult task of persons responsible for avalanche warnings or the closing of roads or ski runs. In favourable cases the traffic can be directly stopped by means of radar when an avalanche is released. The development of the necessary bases and technical realization are important tasks of research. Above all the snow height or the mass of snow (from a snow gauge) or the onset of movement of an avalanche need to be measured automatically. For research it is also interesting to determine the speed of the avalanche and its distribution in given coordinates—along and across the avalanche track. With automatic snow gauges two operating methods have proved successful : (1) ultrasonic sounding from a point above the snow; (2) absorption of cosmic radiation; apparatus for detecting this can also be built into the soil of a slope in the avalanche release zone. The moment of avalanche release can be identified by means of radar in the X-band with moving-target indicator and micro-computer evaluation.
Fracture Mechanical Models of Dry Slab Avalanche Release
Authors: McClung David M. 
Published: September 2017

AbstractExperimental evidence shows that snow is a pressure-sensitive, dilatant, strain-softening material in slow, constant-rate shear deformation. When strain-softening initiates in a weak layer underneath a snow slab, avalanche release is hypothesized to be possible with or without loading. Specifically, two cases are discussed : (i) a shear-crack-like disturbance can initiate by formation of a slip surface in the weak layer and traverse the layer by a self-propagating progressive failure with or perhaps without loading; (ii) a self- propagating shear instability can develop when a region of the weak layer is driven past peak shear strength by loading. These cases represent the extremes in weak-layer deformations under which strain-softening failures might precipitate avalanche release. For these cases the associated fracture sequences, fracture geometry, time scale of release, and temperature- related effects are consistent with the known facts of dry-slab avalanche release.
Spatial Patterns of Snow Accumulation in the Alpine Terrain
Authors: Alford Donald 
Published: September 2017

AbstractA model, relating spatial patterns of snow accumulation in the alpine belt of major mountain ranges to the angular relationship which exists among terrain features such as cirque basins, mean storm-path trajectories, and incident solar radiation, is presented together with a limited amount of relevant empirical data. It is suggested that an “orientation gradient” exists in both the temporal and spatial variation of accumulation and ablation in the alpine terrain, the importance of which varies as some function of the relative control exerted by wind redistribution of snow and of direct incident solar radiation on the accumulation and ablation processes. The data obtained to date suggest that the importance of the orientation gradient varies widely among the mountain ranges studied, being a good predictor of snow distribution patterns in the Front Range of the Colorado Rockies and the Snowy Range in southern Wyoming, both of which are relatively windswept, while in the much less windy Bridger Range, in south-western Montana, both orientation and elevation appear to contribute on an almost equal basis. An indirect method of estimating relative amounts of annual mass turnover, using eleven glaciers located in the Wind River of west central Wyoming, is presented.
Crack propagation and fracture resistance in saline ice
Authors: DeFranco Samuel J. , Dempsey John P. 
Published: September 2017

AbstractCrack propagation in saline ice (a model sea ice) is investigated in this study in an attempt to understand the processes of crack growth at one loading rate and two temperatures. As has been previously observed in cold sea ice and warm or cold fresh-water ice, crack growth occurs in initiation/arrest increments. The energetic stability criteria of crack growth are examined in saline ice and crack growth is characterized in terms of the fracture-resistance parameter KR. This paper offers the development of a new fracture geometry capable of sustained stable crack growth and the presentation of fracture-resistance curves for saline ice at −25° and −15 C. The important findings of this paper are that: (i) in warm saline ice, extensive local crack-tip damage is accompanied by a limited amount of slow, stable crack extension; (n) fracture in cold saline ice is characterized by locally negative KR behavior; and (iii) fracture in cold or warm saline ice is characterized by globally positive KR curve behavior.
Variations of near-surface firn density in the lower accumulation area of the Greenland ice sheet, Pâkitsoq, West Greenland
Authors: Braithwaite Roger J. , Laternser Martin , Pfeffer W. Tad 
Published: September 2017

AbstractFirn-density variations have been studied in the lower accumulation area of the Greenland ice sheet (1440-1620 m a.s.l.) near Pâkitsoq, West Greenland. The main control on density in the near-surface firn layer (of 5-10 m thickness) is the formation of ice layers by the refreezing of meltwater that reaches depths of 2-4 m below the surface. The density variations are described by the ratio of annual surface melt M to the annual accumulation C. The ratio M/C is about 0.6 at the run-off limit (at about 1400 m a.s.l. in the study area) where refreezing of meltwater transforms snow into impermeable ice. The mean density of near-surface firn decreases with elevation, reflecting a decrease in melt with elevation. There is a surprising decrease in firn density at depths of more than about 4 m below the 1991 summer surface, which reflects lower melt rates and/or higher accumulation in the early 1980s and late 1970s when this firn was passing through the surface layer. The formation of such low-density firn may have partially contributed to the 1978-85 thickening of the ice sheet observed by satellite-radar altimetry. Near-surface firn density is therefore very sensitive to climate change and might be an attractive target for climate monitoring.
An investigation of terrain irradiance in a mountain-glacier basin
Authors: Gratton Denis J. , J. Howarth Philip , Marceau Danieile J. 
Published: September 2017

AbstractA remotely sensed method of assessing radiative-transfer processes which considers distinctive zones in the mountain-glacier drainage basin, increases the potential for comprehensive radiative-exchange analysis. By investigating terrain-reflected and terrain-emitted radiation using Landsat-5 Thematic Mapper images and digital elevation data, the objective of this study is to demonstrate the importance of local exchange in the computation of net shortwave and longwave radiation. The results show that terrain-reflected radiation estimates are required to calculate the total shortwave spectral irradiance in all parts of the basin This is necessary to compute accurate surface-cover reflectance and albedo values from the satellite imagery. Furthermore, the assessment of the terrain-emitted radiation explains why, especially on a clear day, the snow and ice covers in many parts of the basin have a very small longwave radiation deficit.
Temperature and movement measurements at a bergschrund
Authors: Mair Rudolf , Kuhn Michael 
Published: September 2017

AbstractThe highest, nearly stationary crevasse that occurs on most alpine glaciers is commonly called a bergschrund. It has often been believed to form when the main ice body below slides downward and thus separates from the thin, steep ice above, which is supposed to remain frozen to its bed. In order to verify or refute this assumption, temperatures and ice motion were recorded at several points in and around a bergschrund on Daunferner, a glacier in the Stubai Alps in Tyrol, Austria. Both measurements and observations indicated that the ice above the bergschrund was sliding as well and that the crevasse formed at a place where ice thickness, deformation and sliding velocity were markedly increasing.At the same time a randkluft, i.e. a deep crevasse between the headwall and the glacier, was observed to open, clearly the result of ice flow and not due to melting as previously believed.
Simulation of ice accretion on a cylinder due to freezing rain
Authors: Szilder Krzysztof 
Published: September 2017

AbstractA hybrid analytical and random-walk model has been developed to predict the shape of ice accreted on a horizontal cylindrical insulator due to freezing rain. The freezing rain occurs with the temperature of the vertically falling raindrops above the freezing point and the air temperature below freezing. The analytical model calculates the angular distribution of the water-film temperature and the location where freezing begins. The random-walk model predicts the accretion shape. The two random-walk model parameters, the freezing probability and the shedding parameter, are expressed as functions of the atmospheric conditions. The model predicts a variety of realistic accretion shapes from cylindrical to icicle-like. Model verification based on comparisons with other models and with experimental results demonstrates quantitatively and qualitatively the credibility of this new modelling approach.
Characteristics of Ice Flow in Marie Byrd Land, Antarctica
Authors: Rose K. E. 
Published: September 2017

AbstractExtensive radio echo-sounding has mapped the part of West Antarctica between Byrd Station, the Whitmore Mountains, the Transantarctic Mountains, and the Ross Ice Shelf. The ice sheet in this area is dominated by five major sub-parallel ice streams (A–E), which are up to 100 km wide and extend inland from the grounding line of the Ross Ice Shelf for about 400 km. Their positions have been determined by crevassing seen on radio echo-sounding records, trimetrogon photographs, and Landsat imagery. The ice streams are characterized by their flat transverse cross-sections, while the intervening ice sheet exhibits domes and ridges. Ice flow lines are defined from the ice-surface contour pattern and the trend of the ice streams. It is apparent from this work that the flow line passing through Byrd Station joins ice stream D.The bedrock of the area is relatively smooth near the Ross Ice Shelf, becoming rougher near Byrd Station and especially so near the Whitmore Mountains. Bedrock troughs, which control the positions of the ice streams, are believed to have a tectonic origin.In this paper the role of the ice streams in the glaciological regime of West Antarctica is investigated from radio-echo data and estimates of balance velocity, basal shear stress, and basal temperatures.
Results from the I.A.G.P. Flow-Line Study Inland of Casey, Wilkes Land, Antarctica
Authors: Budd W. F. , Young N. W. 
Published: September 2017

AbstractIn order to determine accurate velocities of the ice sheet in the interior of Antarctica, approximately along a flow line, a detailed trilateration net was established in 1973 from the summit of Law Dome (100 km inland) to about 250 km south near the 2000 m contour. The net consisted of a double line of markers approximately 10 km apart with all sides and diagonals of the quadrilaterals measured with telluro-meters. In addition, satellite doppler survey positions and astronomical azimuths were determined at about 50 km intervals to control the net on the large scale. Other measurements carried out en route included: continuous barometric levelling, radio echo-sounding, gravimetry, accumulation, and surface sampling. The route was close to an earlier traverse route which reached Vostok in 1962 and along which other data, including snow-surface temperatures and temperature–depth gradients, were determined.The trilateration net was re-surveyed in 1975 allowing velocities and strain-rates to be determined. The results indicate that the ice sheet is close to balance in this region.Therefore, the measured velocities were used together with “balance velocities”, further inland, to carry out a modelling study of a flow line, to derive particle trajectories, ages, temperature profiles, and “dynamics velocities”, from a flow law. The results provide further insight into the dynamics and flow properties of the ice sheet.
The Margin of the Greenland Ice Sheet at Isua
Authors: Colbeck S. C. , Gow A. J. 
Published: September 2017

AbstractField studies at a particular place at the margin of the Greenland ice sheet have provided information about the ice sheet. Ice temperatures were measured in five drill holes, two of which reached the unfrozen area of basal melting. Surface water entered these two bore holes, reaching the base in one, but remaining 59 m above the base in the other. The existence of this water conduit or fracture at 240 m depth, the calculated temperature profiles, and the local bedrock configuration suggest an area of stationary ice overridden by the ice sheet. This situation suggests creep rupture at depth in the ice sheet. Ice-fabric analysis made above 240 m depth shows patterns similar to fabrics elsewhere near the margin in zones of low deviatoric stress. Unfortunately no cores were obtained below that depth where stationary ice may exist.
The Dynamics of Marine Ice Sheets
Authors: Thomas Robert H. 
Published: September 2017

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.
Ice Shelves: A Review
Authors: Thomas Robert H. 
Published: September 2017

AbstractIce shelves form where ice flows off the Antarctic ice sheet onto the sea to produce rather flat slabs of floating ice which, for the theoretician, are the simplest of all large ice masses. Boundary conditions are well defined, conditions change very slowly over distances that are large compared with ice thickness, and horizontal velocities are independent of depth. Unconfined ice shelves can be used as giant creep machines to investigate the ice flow law at low stresses. Further inland, where movement is hampered by obstructions such as grounded ice rises and by shear between the ice shelf and its sides, the ice shelf transmits a backpressure which tends to restrict drainage from the ice sheets that feed it. Wastage from ice shelves is principally by calving and by bottom melting. There has been no direct measurement of bottom-melting rates, but indirect evidence suggests that, near the seaward edges of ice shelves, bottom-melting rates may exceed one metre per year, with significant melting within about 100 km of the ice front. Further inland there may be bottom freezing, and analysis of cores taken from the Amery Ice Shelf indicate that bottom-freezing rates average 0.5 m a–1over a distance of 200 km. Such high freezing-rates are probably exceptional, and, beneath the Ross Ice Shelf, freezing appears to be insignificant even at a distance of 400 km from the ice front.Because of their accessibility ice shelves have been studied in considerable detail, but many problems remain. In particular we need to improve our understanding of basal flux, ice-shelf dynamics near the grounding line, the calving of icebergs, and the state of equilibrium of ice rises. In addition there is a clear need for basic data from the Filchner-Ronne ice shelf.
Finite-Element Simulation of the Barnes Ice Cap
Authors: Emery J. J. , Hanafy E. A. , Holdsworth G. H. , Mirza F. 
Published: September 2017

AbstractThe finite-element method is being used to simulate glacier flow problems, with particular emphasis on the surge behaviour of the Barnes Ice Cap, Baffin Island. Following an advanced feasibility study to determine the influence of major factors such as bed topography and flow relationships, a refined simulation model is being developed to incorporate realistically: the thermal regime of the ice mass; large deformations during flow and sliding; basal sliding zones; a temperature and stress dependent ice flow relationship; mass balance; and three-dimensional influences. The findings of the advanced feasibility study on isothermal, steady-state flow of the Barnes Ice Cap are presented in the paper before turning to a detailed discussion of the refined simulation model and its application to surging. It is clear that the finite-element method allows necessary refinements not available to analytical approaches.
A Numerical Investigation of The Large Scale Dynamics of Sea Ice
Authors: Hibler W. D. 
Published: September 2017

AbstractSeveral numerical simulations of the Arctic ice cover over a seasonal cycle are carried out. Two different types of constitutive laws are examined: rigid plastic and linear viscous. In both cases, the strength of the ice interaction is taken as a function of ice thickness and compactness. The thickness and compactness, in turn, evolve according to continuity equations which include thermodynamic source and sink terms. The simulations with the rigid-plastic law reproduce reasonable geographical ice-thickness variations, ice outflow, and ice-velocity characteristics. The viscous simulations (especially the Newtonian viscous case) produce less satisfactory geographical ice thickness variations, and near-shore velocity characteristics. In addition the Newtonian-viscous simulation produces highly unrealistic ice-edge effects in summer. The results are discussed in terms of the relative magnitudes of the shear and compressive strengths, and in terms of the non-linear versus linear dependence on deformation in the ice rheology. The portion of this study employing a plastic constitutive law is published in full in Journal of Physical Oceanography, Vol. 9, No. 4, 1979, p. 815–46.
Surface Contours and Flow Pattern of a Perfectly Plastic Three-Dimensional Ice Sheet With Arbitrary Bottom and Edge Topography
Authors: Reeh Niels 
Published: September 2017

AbstractThe differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple cases, viz. (1) an ice sheet on a horizontal base with an arbitrary curve as edge and (2) an ice sheet ona plane but sloping bed, with an edge composed of straight-line segments. The solutions are discussed in particular with reference to the development of ice divides and ice streams.