bluuebunny/crossref_metadata_2025 huggingface dataset:
Drift-Ice Abrasion Marks along Rocky Shores
Authors: Dionne Jean-Claude
Published: September 2017

Drift-ice abrasion marks are common along present-day rocky shorelines in cold regions. They include polished surfaces, scratches, striations, small grooves, and minor friction cracks. Most are found on relatively soft rocks like shale, sandstone, limestone, dolomite, and basalt, and occasionally on harder rocks like granite and gneiss. They were made by rock fragments frozen at the base of ice cover or by ice floes pushed onshore by wind or dragged along the bottom by waves, tides, and currents. They are found both in the modern and Pleistocene marine, lacustrine, and fluvial environments. Along the Hudson Bay eastern shoreline, these abrasion marks are superimposed on glacially polished and striated surfaces. Along the St. Lawrence Estuary, they are more common on boulders in the tidal zone. Characteristics of drift-ice abrasion marks are described and their significance is pointed out.
The Mathematical Model of Ice Sheets and the Calculation of the Evolution of the Greenland Ice Sheet
Authors: Grigoryan S.S , Buyanov S.A , Krass M.S , Shumskiy P.A
Published: September 2017

An evolutionary mathematical model of ice sheets is presented. The model takes into account the basic climatic and geophysical parameters, with temperature parameterization. Some numerical data derived from experiments on the Greenland ice sheet are received. At present the Greenland ice sheet is found to be in a state essentially different from a stationary one corresponding to modern climatic conditions.
Greenland ice-sheet surface properties observed by the Seasat-A scatterometer at enhanced resolution
Authors: Long David G. , Drinkwater Mark R.
Published: September 2017

For 3 months in 1978, the 14.6 GHz Seasat-A scatterometer (SASS) measured the normalized microwave-radar back-scatter coefficient of the Earth’s surface for the purpose of estimating near-surface vector winds over the ocean. SASS also made back-scatter measurements over land and ice regions; however, the application of this data has been limited due to the low (50 km) resolution of the measurements. Using a new technique for generating 6 km enhanced-resolution SASS images of the radar back-scatter characteristics, we present a study of the 1978 condition of the Greenland ice sheet. We derive a time-series of back-scatter images spanning the period July–September 1978. These images show the extent of summer ablation along the ice-sheet periphery. Using the data and models relating firn structure and condition to radar back-scatter characteristics, we delineate and map the seasonal extent of zones which appear to correspond to dry-snow, percolation, wet-snow, and ablation facies, over virtually the entire ice sheet. The results provide a base line with which to compare current (ERS-1) and future Greenland radar maps of snow-and ice-surface conditions.
TV-video observations of englacial voids in Storglaciären, Sweden
Authors: Allan Pohjola Veijo
Published: September 2017

TV-video observations of four boreholes in Storglaciären, Sweden, revealed that 1.3% of the observed ice column was composed of englacial voids. The form of the voids is presented by photographs from the video. It is suggested that they are openings into englacial channels and cavities which were intersected during drilling. The observations further showed that about 11% of the ice column consisted of air-bubble-poor blue-ice inclusions. The observations show a relation between the blue-ice inclusions and the voids, which indicates that the origin and development of these features are coupled to each other. It is suggested that crevasses in the accumulation area are an important factor in this process.
Glacial land forms indicative of a partly frozen bed
Authors: Kleman Johan , Borgström Ingmar
Published: September 2017

In parts of the core area of the Fennoscandian ice sheet relict periglacial surfaces occur. The boundary between periglacial and glacial landscapes is often sharp and erosional, with fluting truncating patterned ground. The periglacial surfaces are older than the last ice sheet and are interpreted to represent patches of continuous frozen-bed conditions. A specific land-form assemblage occurs at the edges of such patches. On the basis of three type localities along the eastern rim of the Scandinavian mountains, four thermal boundary land forms, characteristic of the frozen-patch environment, are defined. Stoss-side moraines and transverse till scarps, not previously described, are interpreted to have formed in detachment zones where soil frozen to the glacier overlies thawed soil. The detachment zones are located where subglacial warming raises the phase-change surface (water/ice) until it intersects the soil layer up-and down-glacier from residual frozen-bed patches. The up-glacier ends of frozen-bed patches are located on topographic highs, but down-glacier the location of lateral sliding boundaries is occasionally independent of topography. The identification of relict surfaces and thermal boundary forms can improve paleo-ice-sheet models by providing estimates of the extent of frozen-bed conditions.
Brittle compressive failure of salt-water columnar ice under biaxial loading
Authors: Smith T. R. , Schulson E. M.
Published: September 2017

The brittle failure of saline columnar ice was investigated under biaxial compression at and −10° and −40°C over the range 0 ≤ RA < 1 where RA is the ratio of the intermediate to major principal compressive stress. The major principal stress and the intermediate (confining) stress were orthogonal to the columnar axes (type-A confinement); both stresses and the c-axes of the grains were co-planar. The results confirm earlier work by Hausier (1981) and Timco and Frederking (1983, 1986) on saline ice and follow similar behavior to fresh-water columnar ice found by Smith and Schulson (1993) and Frederking (1977). Failure stress and failure mode are sensitive to the confinement and two regimes of behavior are found: the failure stress first rapidly increases with RA in the range 0 ≤ RA < RT and then tends to decrease for RA > Rt. The transition stress ratio, Rt changes from ≈0.2 at −10°C to ≈0.1 at −40°C. The failure mode changes from axial splitting to shear faulting in the loading plane for 0 < RA < Rt. Above Rt failure changes to a combined mode of splitting across the columns and shear faulting out of the loading plane. The failure-stress envelope is of a truncated Coulomb-type. Damage studies show wing cracks and local fragmentation of grains involving the brine pockets. The results are explained in terms of Coulombic sliding and Hertzian crack mechanics.
Mass-balance estimates on the glacier complex Kongsvegen and Sveabreen, Spitsbergen, Svalbard, using radioactive layers
Authors: Lefauconnier Bernard , Hagen Jon Ove , Pinglot Jean Francis , Pourchet Michel
Published: September 2017

Analyses of total β and γ radioactivity have been carried out on ten shallow ice cores collected in 1989 and 1990 on Kongsvegen and Sveabreen, Spitsbergen. No peak of total β radioactivity, corresponding to the Chernobyl accident (1986), can be identified. Chernobyl layers were identified by 137Cs and 134Cs activities, and a signal from the nuclear tests in Novaya Zemlya (1961–62), was detected at one location by 137Cs activity. The mean net accumulation for the periods 1986–89 and 1962–88 was estimated for both glaciers. Using topographic data, the mean net ablation on Kongsvegen was estimated for the period 1964–90 and the mean net balances were calculated. The results agree with recent direct glaciological balance measurements. For the period 1986–89, the net accumulation was higher on Sveabreen than on Kongsvegen, and the equilibrium-line altitudes (ELA) were around 450 and 520 m a.s.l., respectively. Kongsvegen had a positive balance of 0.11 m w.eq. and Sveabreen was in equilibrium, whereas for the last 26 years the balance of Kongsvegen was slightly negative (−0.10 m w.eq.) and the ELA was around 560 m a.s.l.
Spatial and temporal patterns in snow accumulation, western Dronning Maud Land, Antarctica
Authors: Isaksson Elisabeth , Karlén Wibjörn
Published: September 2017

During the Swedish Antarctic Expedition to Dronning Maud Land, Antarctica, 1988–89 the net accumulation was estimated for an area from the coast to about 400 km inland. Stake measurements were used to obtain the spatial variability and firn cores were used for the temporal variability. The mean annual accumulation for the period 1976–88 is about 0.4mw.e. for Riiser-Larsenisen and about 0.3mw.e. for the area above the grounding line. The accumulation rate at higher altitudes, > 2500 m a.s.1., is about 0.1 m w.e. for 1955–88. One record from the ice shelf covers the period 1957–88, and suggests an increase in accumulation of about 12%. Between 1976 and 1988, the accumulation has decreased by about 50%, most likely due to lower temperatures as suggested by the temperature record from Halley.
Radio Echo-Sounding Studies of Englacial Water Movement in Variegated Glacier, Alaska
Authors: Jacobel Robert , Raymond Charles
Published: September 2017

Radio-echo returns from internal reflectors were monitored for three weeks during surge motion on Variegated Glacier, Alaska in July 1982. A monopulse transmitter with 3 MHz center frequency was fixed on the glacier surface near the equilibrium line. Data were recorded on magnetic tape approximately three times daily and contain both amplitude and phase information. The frequency spectrum of returned radiation from englacial scatterers shows peaks in the 12 to 30 MHz range which places constraints on the size and geometry of the scatterers. Timing of variations in the amplitude and frequency of returned radiation were found to coincide with changes in glacier velocity, basal water pressure, and surface melt rate. These changes in the echo pattern are interpreted in terms of the redistribution of water in englacial channels and cavities connected to the bed some distance down-glacier. This connection has large hydraulic resistance compared to a bore hole connected vertically to the bed. The inflow of water to the cavities from surface melt and rain and the drainage are generally in equilibrium except in times of changed surface input and during surge pulses. In the latter case, water may fill these cavities due to increased pressure at the bed associated with the motion pulse. The information obtained is therefore complementary to bore-hole water pressure levels but cannot duplicate it. This is apparently due to fundamental differences in the hydraulics of the natural cavity and conduit system, and a bore hole connected vertically to the bed.
Sedimentary Processes and Buried Ice Phenomena in the Pro-Glacial Areas of Spitsbergen Glaciers
Authors: Hambrey M. J.
Published: September 2017

Observations at the snouts of several glaciers in Spitsbergen indicate that, between their present apparent limits and the moraines dating from the maximum Holocene extent of ice, wide areas of outwash deposits underlain by dead glacier ice occur. Such ice was visible at a number of localities. Indirect evidence of dead ice includes kettle-holes, collapse structures and, in one case, a subglacial melt stream emerging as a fountain within one such plain. Aufeis, formed in early winter, can sometimes also be preserved in the long term if covered by fluvio-glacial material. The presence of such ice has implications for the interpretation of soft-sediment structures in glacigenic successions. Previously, many folds and faults have been interpreted as resulting from active ice overriding or pushing the sediment. Simple ablation beneath the sedimentary layer in question also gives rise to similar structures.
Relation between the Mass Balance of Western Canadian Mountain Glaciers and Meteorological Data
Authors: Letréguilly Anne
Published: September 2017

The mass balance, summer balance, winter balance, and equilibrium-line altitude of three Canadian glaciers (Peyto, Place, and Sentinel Glaciers) are compared with the meteorological records of neighbouring stations for the period 1966—84. While Peyto Glacier’s mass balance is almost entirely related to summer temperature, Sentinel Glacier’s mass balance is mostly controlled by winter precipitation. Place Glacier is influenced by both elements. Statistical reconstructions are presented for the three glaciers, using the best regression equations with the meteorological records since 1938.
A Stochastic Model of Atmospheric Rime Icing
Authors: Gates E.M. , Liu A. , Lozowski E.P.
Published: September 2017

The accumulation of rime ice on structures, due to the impact and freezing of small water droplets, has been modelled as a stochastic process. Individual droplets are introduced into the flow field about the structure at a random position. Their trajectories are then calculated to determine the position of impact on the structure, or on previously impacted droplets. By assuming that the droplets maintain their shape on impact, the modelled accretion is gradually built up, one droplet at a time.

In the present paper, attention has been limited to a circular cylinder as the collecting structure, and it has been assumed that the flow field and the ice accumulation are strictly two-dimensional. With these assumptions, the influence of the droplet/cylinder diameter ratio and of the air speed upon the resulting predictions has been investigated. The main feature of interest in the model prediction is the development, near the edges of the accumulation, of discrete structures called “rime feathers”. The mechanism for the growth of these rime feathers is described, and a comparison is made between the characteristics of the predicted structures and of some natural rime feathers grown in an icing wind tunnel.
Ice-shelf Response to Ice-stream Discharge Fluctuations: II. Ideal Rectangular Ice Shelf
Authors: Macayeal Douglas R. , Lange Manfred A.
Published: September 2017

Abstract. Ice-shelf thickness and velocity anomalies resulting from ice-stream discharge fluctuations are calculated for an ideal ice shelf fed by a single ice stream and confined within a rectangular coastal geometry. Ice-shelf response to periodic forcing is found to be linear (thickness and velocity anomalies oscillate at the forcing frequency, and response scales with the forcing). Thickness anomalies are trapped near the ice-stream outlet and propagate down-stream at a slow, advective time-scale. Velocity anomalies tend to be widespread and propagate instantaneously throughout the ice-shelf environment. Ice-shelf response is sensitive to ice-stream fluctuation time-scale in the manner of a low-pass filter; longer forcing time-scales produce more widespread ice-shelf response. If ice-stream velocity and thickness fluctuations are in phase, thickness-anomaly maxima typically occur down-stream of the ice-stream outlet. This effect may determine where ice rumples and rises are likely to form in response to stochastic ice-stream variability.
Apron Entrainment at the Margins of Sub-Polar Glaciers, North-West Ellesmere Island, Canadian High Arctic
Authors: Evans David J.A.
Published: September 2017

From observations on the sub-polar glaciers of Phillips Inlet, north-west Ellesmere Island, neither complex basal thermal regimes nor internal thrusting need be invoked to explain all types of debris distribution in the basal ice of sub-polar glaciers. Debris is present in the terminal ice cliffs as: (1) debris-poor folia expressing internal flow patterns; (2) debris-rich bands of various thickness; and (3) augens or clots. Debris-rich bands and augens are concentrated predominantly in the basal ice, contain a wide range of grain-sizes, cut across debris-poor folia, rarely extend >1 m laterally, and are irregularly spaced.

Observations on patterns of entrainment and contemporary processes at ice margins, together with clast-shape analyses, suggest that the recycling and re-incorporation of fluvial/deltaic sediment, aprons, and pro-glacially thrusted blocks at the ice face are an alternative process of debris entrainment to basal plucking and large-scale freeze-on at the base of the glacier. The most active processes observed at the glacier margins are fluvial, and the origins of some debris-rich bands and augens are linked to thermal-erosional niches and abandoned meanders in the base of the glacier cliff face. Because the large-scale accumulation of ice-cored debris at glacier snouts represents periods of increased run-off and snout recession (specifically during the early Holocene), basal and englacial debris concentrations resulting from glacial over-riding and re-incorporation have great palaeoclimatic significance.
An Energy and Mass Model of Snow Cover Suitable for Operational Avalanche Forecasting
Authors: Brun E. , Martin Ε. , Simon V. , Gendre C. , Coleou C.
Published: September 2017

A numerical model has been developed to simulate energy and mass evolution of snow cover at a given location, as a function of meteorological conditions: precipitation, air temperature, humidity, wind velocity, and incoming short-wave and long-wave radiation.

This model, named CROCUS, was first tested on a well-instrumented field during a whole winter, showing its ability to simulate the important phenomena affecting the evolution of the snow layers: high temperature gradients, wetting, compaction, and melting-freezing cycles. A second test was conducted at two locations in the French network used for operational avalanche forecasting. Though the weather observations are made there only twice daily, the snow profiles calculated by the model were very close to those obtained once a week by a pit observation. CROCUS proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting.
Mass-Balance Gradients and Climatic Change
Authors: Oerlemans J. , Hoogendoorn N.C.
Published: September 2017

It is generally assumed that the mass-balance gradient on glaciers is more or less conserved under climatic change. In studies of the dynamic response of glaciers to climatic change, one of the following assumptions is normally made: (i) the mass-balance perturbation is independent of altitude or (ii) the mass-balance profile does not change — it simply shifts up and down. Observational evidence for such an approach is not convincing; on some glaciers the inter-annual changes in mass balance seem to be independent of altitude, on others not at all. Moreover, it is questionable whether inter-annual variation can be “projected“ on different climatic states.

To see what a physical approach might contribute, we developed an altitude-dependent mass-balance model. It is based on the energy balance of the ice/snow surface, where precipitation is included in a parameterized form and numerical integrations are done through an entire balance year (with a 30 min time step). Atmospheric temperature, snowfall, and atmospheric transmissivity for solar radiation are all dependent on altitude, so a mass-balance profile can be calculated. Slope and exposure of the ice/snow surface are taken into account (and the effects of these parameters studied). In general, the calculations were done for 100m elevation intervals.

Climatological data from the Sonnblick Observatory (Austria; 3106 m a.s.l.) and from Vent (2000 m a.s.l.; Oetztal Alps, Austria) served as input for a number of runs. Simulation of the mass-balance profiles for Hinterseisferner (north-easterly exposure) and Kesselwandferner (south-easterly exposure) yields reasonable results. The larger balance gradient on Kesselwandferner is produced by the model, so exposure appears to be an important factor here.

Sensitivity of mass-balance profiles to shading effects, different slope, and exposure are systematically studied. Another section deals with the sensitivity to climatic change. Perturbations of air temperature, cloudiness, albedo, and precipitation are imposed to see their effects on the mass-balance profiles. The results clearly show that, in general, mass-balance perturbations depend strongly on altitude. They generally increase down-glacier, and are not always symmetric about the reference state.

For typical climatic conditions in the Alps, we found that a 1 K temperature change leads to a change in equilibrium-line altitude of 130 m. Three factors contribute to this large value; turbulent heat flux, longwave radiation from the atmosphere, and fraction of precipitation falling as snow. Here, the albedo feed-back increases the sensitivity in a significant way.
Early Discoverers XXXVI: W.J. McGee On Glacial Erosion Laws and the Development of Glacial Valleys
Authors: Harbor Jonathan M.
Published: September 2017

In work presented in 1883 and published in full in 1894, W.J. McGee made one of the first clear attempts to outline the main morphologic differences between glaciated valleys and valleys developed by processes dominant in more temperate areas. Moreover, with an unprecedented analysis of glacial erosion, he attempted for the first time to explain the evolution of glacial land forms in terms of theoretical predictions of patterns of erosion under valley glaciers. In the latter half of the nineteenth century, there was fierce debate over whether glaciers were even capable of significant erosion, so it is perhaps not surprising that McGee’s analysis of glacial erosion processes and land-form development received little attention in his own time. Despite this, McGee’s work provided some of the first really convincing glacial explanations for the development of land forms such as hanging valleys and U-shaped valleys, and these were developed more fully in later work by Davis (1900) and Gilbert (1903). In modern research, the use of theoretical erosion laws and a knowledge of ice dynamics to develop models of land-form development is emerging as a major theme in glacial geomorphology, marking a return to the methodology pioneered by W.J. McGee.
Field Techniques for Experimental Stress Analysis in Arctic Sea Ice
Authors: Cochran G. V. B.
Published: September 2017

Increasing interest is being directed toward studies involving measurement of strain and strain-rates in sea and glacier ice. A number of techniques for obtaining these data over gauge lengths ranging from 1 m to several kilometers have been reported, but there has been little experience with shorter lengths. Use of commercially available electrical resistance strain-gauges (length 5–20 cm) intended for embedment in concrete offers a new approach in which multiple gauge, two- and three-dimensional arrays can be installed in ice with minimum effort and monitored with portable equipment. This report describes a pilot study designed to demonstrate the use of three types of electrical resistance strain gauges in sea ice under exposed field conditions. Results include detection of variations in strain fields related to tidal currents.
Simultaneous Measurements of Stability Indices and Characteristic Parameters Describing the Snow Cover and the Weather in Fracture Zones of Avalanches
Authors: Gubler H.
Published: September 2017

Stability indices at different slope aspects and characteristic parameters describing the snow cover and the weather conditions are recorded simultaneously and automatically in potential fracture zones of avalanches during the whole winter season. A remote, solar-powered system including measurements of snow depth, mass flux of wind-blown snow and of the snow temperature profile as well as on-line and off-line data processing has been developed and tested. The results show that this type of data-recording and processing system makes quantitative case studies of natural stability variations possible.
Calculations of Avalanche Friction Coefficients from Field Data
Authors: Martinelli M. , Lang T. E. , Mears A. I.
Published: September 2017

The friction coefficients needed to solve Voellmy’s avalanche-dynamics equations and as input to the numerical, finite-difference computer program AVALNCH are calculated from case studies. The following coefficients of internal frictionvand of surface frictionfworked well for program AVALNCH: for midwinter dry snowv =0.5 to 0.55 m2/s andf= 0.5 to 0.55; for hard slabv =0.7 to 0.8 m2/s andf =0.7 to 0.8; for fresh, soft slabv= 0.4 to 0.5 m2/s and f = 0.4 to 0.5. The program predicted run-out distance well for a variety of conditions but performed less well in cases of sharp, adverse grade in the run-out zone. For the Voellmy approach, large design-size avalanches required turbulent friction coefficients ξ of 1200 to 1600 m/s2and kinetic friction coefficients of 0.15. Two hard-slab avalanches, a slow-moving,wet-slab avalanche, and a soft-slab avalanche that ran through scattered mature timber required ξ of 700 to800 m/s2and μ of 5/V whenVis velocity in m/s. The coefficient of sliding friction for a hard-slab avalanchethat encountered damp snow in the run-out zone was computed directly from movies to be 0.35, 0.43, and 0.32 for three measured sections of the run-out zone.
Observed Maximum Run-Out Distance of Snow Avalanches and the Determination of the Friction Coefficients µ and ξ
Authors: Buser Othmar , Frutiger Hans
Published: September 2017

To fix the limits of different hazards in the avalanche-hazard maps one uses criteria pertaining to avalanche dynamics. These criteria are at present the velocity and the run-out distance of a given avalanche for a given place. In 1955 A. Voellmy published his theory of avalanche dynamics which has widely been used in practical map preparation. Since 1962 his equations have also been used by the Eidg. Institut für Schnee- und Lawinenforschung (EISLF) to calculate avalanche pressures and run-out distances. Furthermore B. Salm (EISLF) developed another equation for the calculation of run-out distances in 1978. Both the equations of Voellmy and of Salm contain two friction coefficients, µ and ξ. Little is known about them and opinions, even among specialists, differ on what values should be given to them.

This paper presents field observations on very long run-out distances. These observations are used to calculate values for pairs of µ and ξ. For avalanche zoning, only extreme values are of interest, i.e. very low values for µ and very high values for ξ. For the calibration of those coefficients, ten avalanches from the winters 1915–16, 1967–68, 1974–75, and 1977–78 have been used. Those avalanches occurred during heavy and intense snowfalls. For those avalanches, the pair µ= 0.155, ξ = 1 120 m/s2 was found for the Voellmy equation and the pair µ = 0.157, ξ =1 067 m/s2 for the Salm equation. These values only partially agree with those used up to date by EISLF. It is recommended for example that for extreme flowing avalanches (newly fallen snow, soft slabs) the pair µ = 0.16,ξ = 1 360 m/s2 be used.
Modeling of Snow flow
Authors: Dent J. D. , Lang T. E.
Published: September 2017

A numerical computer model, based on the finite differencing of the Navier-Stokes fluid equations, is used to simulate snow-avalanche flow. In order to verify and calibrate the numerical model, snow-flow tests 0.20 m deep with flow velocities between 0-18 m/s were conducted. Data concerning position, velocity, and flow depth versus time were collected and compared to model runs on the computer. The frictional force on moving snow is investigated and found to be modeled by a term that is proportional to the square of the flow velocity.
Scale Modeling of Snow–Avalanche Impact on Structures
Authors: Lang T. E. , Dent J.D.
Published: September 2017

Small–scale modeling of flow and impact of snow avalanches is demonstrated to be both feasible and accurate. Geometric, kinematic, and force variables are scaled correctly under equivalence of Froude number between prototype and model using sifted snow as the model fluid. Physical and computer–simulated impact processes show correspondence, so that computer modeling is demonstrated to be a viable tool in flow and impact predictions.
A Model For Snow-Slab Failure Under Conditions Of Dynamic Loading
Authors: Johnson Jerome B.
Published: September 2017

A stress-wave model is used to describe snow-slab failure under dynamic loading conditions. This model indicates that dilational waves and shear waves can interact with a thin, weak bedding layer underlying a snow slab causing dilatational and shear stresses in the layer. The magnitude and distribution of stresses in the layer are shown to depend strongly on the height of the loading source above the bedding plane, the difference in impedance between the slab and the loading source, the difference in impedance between the slab and its substratum, and the initial stress magnitude of the loading source. Failure occurs in the bedding layer when the generated stresses exceed the strength of the layer. This causes a loss of shear strength capacity at the bedding plane and a re-distribution of stress in the slab. If the shear capacity is reduced sufficiently the body-force loading of the slab will cause snow-slab failure.
An Experimental Study of Temperature-Gradient Metamorphism
Authors: Marbouty D.
Published: September 2017

The present study was carried out with a view to quantifying the effects of the main parameters ot temperature-gradient metamorphism. Cold-room simulation tests showed crystal growth to be an increasing function of the temperature-gradient modulus with a lower limit of around 0.25 deg/cm. This growth also proved to be a function of temperature itself reaching a maximum at around –5°C Furthermore the shape of depth-hoar crystals was also shown to depend on temperature and to resemble approximately that obtained when crystals are formed in the atmosphere. Temperature-gradient metamorphism is observed to take place at constant density. Increase in crystal size is a decreasing function of density with a lower limit of around 150 kg/m3, below which destructive metamorphism occurs accompanied by packing (similar to ET metamorphism): the upper limit is situated at approximately 350 kg/m3 and no depth-hoar crystals occur above this value. The series of Cold-room simulations enabled a highly simplified model of crystal growth to be constructed.
Municipal Avalanche Zoning: Contrasting Policies of Four Western United States Communities
Authors: Mears Arthur I.
Published: September 2017

Four communities in the western United States (Vail, Colorado; Ketchum, Idaho; Ophir, Colorado; and Juneau, Alaska) have detailed avalanche–hazard mapping available. In response to this detailed information, Vail restricts building in a red (high hazard) zone but permits specially designed buildings in the blue (moderate hazard) zone. Ketchum allows single–family dwellings in red or blue zones regardless of design but will not permit such structures to be rented from the period 15 November through 15 April of each year. Multi–family dwellings in Ketchum hazard zones must be designed for avalanche forces. Ophir will restrict buildings from the red zone and permit specially designed structures in the blue zone. Juneau does not restrict development in any avalanche–hazard zone.
Research on Prevention of Snow-drifts by Blower Fences
Authors: Zhonglong Wang , Yuan Chen
Published: September 2017

The mechanism by which blower fences can protect roads from snow-drifts is investigated, and the variation of the drift-free width behind a blower fence with the dimensions and inclination of the fence and with terrain features has been determined. The results are presented in the form of an equation and a nomogram to help in the design of blower fences.
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

The 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

The 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

This 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

Automatic 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

Experimental 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

A 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

Crack 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

Firn-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

A 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

The 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

A 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

Extensive 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

In 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

Field 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.