bluuebunny/crossref_metadata_2025 huggingface dataset:
A Flow-line Model for Calculating the Surface Profile and the Velocity, Strain-rate, and Stress Fields in an Ice Sheet
Authors: Reeh Niels
Published: September 2017

A flow-line model is presented for calculating the surface profile and the velocity, strain-rate, and stress fields in an ice sheet with given base-elevation profile, ice thickness at the dome (divide), flow-law parameters, mass-balance distribution, and convergence/divergence conditions along the flow line. The model, which is based on a “quasi-similarity” hypothesis as regards the horizontal velocity-depth profiles, accounts for changes along the flow line in the depth distributions of temperature, normal stress deviators, and possible enhanced flow of deep ice of Wisconsin origin. A curvilinear coordinate system is applied with horizontal axes along flow lines and surface-elevation contours, respectively. The flow equations are reduced to two differential equations, one for the surface-elevation profile, and the other for a profile function that determines the depth distributions of velocities and strain-rates. The two equations are coupled through a profile parameter that communicates the influence of velocity-profile changes to the surface-profile equation. It is shown that the variation along the flow line of this parameter should also be considered when deriving flow-law parameters from ice-sheet flow-line data. For a symmetric dome, explicit expressions are derived for the depth distributions of the vertical velocity, strain-rates, and stresses. The strain-rate profiles display an inflection about half-way down the ice sheet, and, in the case of isothermal ice, have surface values 2.2 times their depth-averaged values. The depth distribution of the vertical velocity indicates that a relatively thick layer of almost stagnant ice is present at the ice-sheet base below a dome.
A Model of Icicle Growth
Authors: Makkonen Lasse
Published: September 2017

A theory of icicle growth is presented. It is shown that icicles elongate as hollow tubes of ice with liquid water trapped inside the tip. A time-dependent computer model based on the theory shows that the growth of an icicle is a complicated process, which is very sensitive to the atmospheric conditions and water flux. The shape and weight of icicles predicted by the model agree well with laboratory data.
The Kinetic Friction of Snow
Authors: Colbeck S.C.
Published: September 2017

Three components of the kinetic friction of snow are described but only the lubricated component of friction is treated in detail. This component depends upon the thickness of water films which support a slider on snow grains over a small fraction of its area. The thickness of the film decreases with ambient temperature in a manner which is sensitive to the thermal conductivity of the slider. The minimum value of friction at any temperature is reached at an intermediate value of speed because friction decreases as the slider first begins to move and the films form but then increases at higher speeds because of the shear resistance. At sub-freezing temperatures a small area in the front part of the slider is dry and the friction is high. Once the water film is formed it increases in thickness towards an equilibrium value which can be very sensitive to slider properties, speed, and temperature. It appears that the mechanisms may be very different for hydrophobic and hydrophilic sliders. From the equations derived here it is clear why friction decreases with repeated passes over the same snow.
The Nature and Origin of a Jökulhlaup Near Casey Station, Antarctica
Authors: Goodwin I.D.
Published: September 2017

A jökulhlaup event of 6 months duration occurred near Casey Station, Law Dome, Antarctica, in late March (austral autumn) 1985. This was followed by sporadic outbursts during the austral autumn and winter of 1986. The event is the first recorded outburst of water from beneath a cold ice-cap terminus on Law Dome and, to the author’s knowledge, in Antarctica. From the results of oxygen-isotope and solute analysis, the water was found to have originated as basal melt water. It contained a high total solute load with a dominant enrichment in alkalis, indicting that it had been squeezed through subglacial sediments for an extensive time period. Evidence from the subglacial topography, basal ice exposures, and the sedimentology of nearby supraglacial moraines supports the presence of an ice-marginal subglacial water reservoir as the jökulhlaup source.
Effects of Climatic Perturbations on the Surface-Ablation Regime of the Greenland Ice Sheet, West Greenland
Authors: Ambach W.
Published: September 2017

The shift of the equilibrium-line altitude by climatic perturbations of air temperature δTa, absolute humidity δρv, cloudiness δw and annual accumulation 6c in West Greenland (EGIG profile) is analyzed by heat-balance modelling. The perturbations δTa = +1 K, δρv = +0.25 g m−3, δc = +50 kg m−2 result in a shift of the equilibrium-line altitude of 87.5, 9.8, and −24.3 m, respectively, while perturbations in cloudiness are negligible. The most important influence originates from changing air temperature, as air temperature affects daily heat-flux density of melt and duration of the ablation period. In regimes with negative values of the gradient of annual accumulation, the shift of the equilibrium line is enhanced.
Surface Roughness and Bulk Heat Transfer on a Glacier: Comparison with Eddy Correlation
Authors: Munro D. Scott
Published: September 2017

More than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice. The results proved to be extremely sensitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness lengths were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.
Estimates of Peak Discharge from the Drainage of Ice-Dammed Ape Lake, British Columbia, Canada
Authors: Desloges Joseph R. , Jones David P. , Ricker Karl E.
Published: September 2017

The first known occurrence of outburst flooding at Ape Lake, British Columbia, was in October 1984 following the formation of a subglacial tunnel in an ice dam created by Fyles Glacier. Following tunnel closure, the lake refilled in 150 d and then a second outburst flood occurred in August 1986. During both events, 55% of the Apc Lake volume or 46 × 106m3was released in less than 24 h into the 50 km long, ungauged Noeick River, producing an average discharge of 540 m3s−1. Channel and flood-plain erosion, damage to access roads, bridges, a logging camp, and an airstrip were related to the peak or maximum instantaneous discharge. In the absence of direct measurements, and to facilitate planning for future flood events, several independent methods were employed to estimate peak discharge. A modified version of the Clague-Mathews formula and the slope-area method yield consistent estimates which approach 1600 m3s−1near the ice-dam outlet. Attenuation of the flood peak in Noeick River is as high as 25% in the upper 12 km due to channel and flood-plain storage. Results using Clarke’s (1982) physical-based model suggest lower discharges and may be related to the irregular morphology of Ape Lake. Since Fyles Glacier is in continuous retreat, drainage around the margin of the ice dam which began in the summer of 1987 is expected to continue and no further outburst floods are anticipated.
Distribution of Net Mass Balance in the Vicinity of Crary Ice Rise, Antarctica
Authors: Bindschadler Robert A. , Roberts Eric P. , MacAyeal Douglas R.
Published: September 2017

Calculations of the regional variation of net mass balance around Crary Ice Rise, Antarctica, show significant rates of thickening up-stream of the ice rise and significant thinning down-stream (assuming zero basal melting or freezing). Thickening also is occurring on the south-west side of the ice rise nearest the Transantarctic Mountains. These imbalances imply migration of the rise and help explain its current non-equilibrium shape. The pattern of a suture line down-stream of the rise indicates a quasi-periodic mechanism of rift formation.
The Effect of the Specimen–Platen Interface on Internal Cracking and Brittle Fracture of Ice Under Compression: High-Speed Photography
Authors: Schulson E.M. , Gies M.C. , Lasonde G.J. , Nixon W.A.
Published: September 2017

Uniaxial compression experiments at –10°C at 10−3s−1 on fresh-water, granular ice have established through the use of high-speed photography that internal cracks nucleate preferentially away from the ice/platen (i/p) interface under conditions of i/p contraint, but near the interface under conditions of i/p expansion. Under conditions of little i/p interaction, cracks nucleate more or less randomly throughout the specimen. Correspondingly, the brittle-fracture strength decreases as the i/p interaction changes from compressive to tensile. These effects are explained in terms of the spatial variation of the maximum shear stress and the crack density.
Crystalline Texture of the 2083 m Ice Core at Vostok Station, Antarctica
Authors: Lipenkov V.Ya. , Barkov N.I. , Duval P. , Pimienta P.
Published: September 2017

Crystalline texture and c-axis orientation of the 2083 m ice core at Vostok Station, covering more than 150kyear, reveal the existence of strong anisotropics. Changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries. A smaller growth rate appears to be associated with cold periods. A gradual increase in the horizontal elongation of grains was observed between 350 and 680 m. But, the mean value of the coefficient of the linear dimensional orientation of grains does not change below 700 m.

The c-axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains, forming a vertical girdle pattern. This characteristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longitudinal tension. The rotation of grains was calculated with respect to the total strain, simulating the formation of the girdle fabric pattern. The fabric-enhancement factor was calculated at various depths. It appears that Vostok ice hardens gradually with depth when considering the transverse convergent flow. No significant variation of the enhancement factor was observed with changes in climate and impurity content.
The Age-Depth Profile in the Upper Part of a Steady-State Ice Sheet
Authors: Reeh Niels
Published: September 2017

Simple analytical models are developed in order to study how up-stream variations in accumulation rate and ice thickness, and horizontal convergence/ divergence of the flow influence the age and annual layer-thickness profiles in a steady-state ice sheet. Generally, a decrease/increase of the accumulation rate and an increase/decrease of the ice thickness in the up-stream direction (i.e. opposite to the flow direction) results in older/younger ice at a given depth in the ice sheet than would result if the up-stream accumulation rate and ice thickness were constant along the flow line.

Convergence/divergence of the up-stream flow will decrease/increase the effect of the accumulation-rate and ice-thickness gradients, whereas convergence/divergence has no influence at all on the age and layer-thickness profiles if the up-stream accumulation rate and ice thickness are constant along the flow line.

A modified column-flow model, i.e. a model for which the strain-rate profile (or, equivalently, the horizontal velocity profile) is constant down to the depth corresponding to the Holocene/Wisconsinan transition 10 750 year BP., seems to work well for dating the ice back to 10 000–11 000 year B P. at sites in the slope regions of the Greenland ice sheet. For example, the model predicts the experimentally determined age profile at Dye 3 on the south Greenland ice sheet with a relative root-mean-square error of only 3% back to c. 10 700 year B.P. As illustrated by the Milcent location on the western slope of the central Greenland ice sheet, neglecting up-stream accumulation-rate and ice-thickness gradients, may lead to dating errors as large as 3000–000 years for c. 10 000 year old ice.

However, even if these gradients are taken into account, the simple model fails to give acceptable ages for 10 000 year old ice at locations on slightly sloping ice ridges with strongly divergent flow, as for example the Camp Century location. The main reason for this failure is that the site of origin of the ice cannot be determined accurately enough by the simple models, if the flow is strongly divergent.

With this exception, the simple models are well suited for dating the ice at locations where the available data or the required accuracy do not justify application of elaborate numerical models. The formulae derived for the age-depth profiles can easily be worked out on a pocket calculator, and in many cases will be a sensible alternative to using numerical flow models.
Two Models for Estimating Climate‒Glacier Relationships in the North Cascades, Washington, U.S.A.
Authors: Tangborn Wendell
Published: September 2017

Two models based on standard observations of precipitation, temperature, and run-off at low-altitude weather and gaging stations have been devised to calculate annual glacier balances in the North Cascades of Washington. The predicted glacier balances of the Thunder Creek basin glaciers, determined by a run-off–precipitation (RP) model during the 1920–74 period, are compared with balances predicted by a precipitation–temperature (PT) model for the same period. Annual balances determined by the PT model are also compared with balances measured by field techniques at South Cascade Glacier since 1958. In the PT model, winter snow accumulation (winter balance) is determined by winter (October–April) precipitation observed at the Snoqualmie Falls weather station. Summer (May–September) ablation (summer balance) on the glaciers is estimated by a technique which utilizes maximum and minimum air temperatures, also observed at Snoqualmie Falls. Ablation calculations incorporate summer cloud cover as a variable by using a relationship between cloud cover and the range in daily maximum and minimum air temperatures.

Annual mass changes for the 1884–1974 period in both South Cascade Glacier and the Thunder Creek glaciers were reconstructed by utilizing the PT model. The fluctuations in glacier mass during this period generally agree with historical observations and show that a definite change in glacier activity from marked recession to stability or an advancing state occurred about 1945. During the 1900–45 period, South Cascade Glacier lost mass at a rate of 1.4 m per year and the Thunder Creek glaciers (which are at a higher altitude) at 1.1 m per year.

These models suggest that the relationship of glacier mass balance to precipitation and temperature is a very sensitive one. It appears from these studies that a decrease in summer air temperature of just over 0.5 deg or an increase in winter accumulation of slightly more than 10% (350 mm) from the 1920–74 average would cause these glaciers to grow continuously.
A Thermohydrodynamic Model of an Ice Sheet
Authors: Verbitsky M. Ya. , Chalikov D. V.
Published: September 2017

The purpose of this paper is to consider an ice-sheet model based on joint solution to the dynamic equations and equations of heat conductivity in which the surface relief is one of the unknown functions. The proposed model is applicable to calculations of the Antarctic ice sheet. Results of a numerical experiment for present values of the temperature of the ice surface and precipitation as well as for their separate and simultaneous increase by 2, 4, or 6 deg and 10, 20, or 30% are given.
The Pendular-Funicular Liquid Transition in Snow
Authors: Denoth A.
Published: September 2017

The way free water is distributed around contact points of ice grains is recorded by measuring the dielectric constant of the porous system which constitutes snow. Within the saturation range of 11% to 15% of the pore volume, a transitional range from the “pendular” to the “funicular” mode of distribution of free water occurs. By measuring the drainage-flow of free water through snow, additional information as to the upper limit of the pendular distribution is obtained. This upper limit is reached at a saturation of approximately 14% of the pore volume.
Dynamic Behaviour of Dislocations in HF-Doped Ice Ih
Authors: Perez J. , Maï C. , Tatibouët J. , Vassoille R.
Published: September 2017

A model of dislocation glide in ice Ih was recently proposed. This model was developed on certain assumptions, namely that transitions occur through cooperative movements of H2O molecules in the non-crystalline core of dislocations. A relation between the velocity vd of linear defects and shear stress τ or temperature T is obtained. This relation shows that vd varies linearly with τ at low values of τ and (or) T but varies more rapidly at higher stresses; this non-linearity is more pronounced the higher the temperature. Such an analysis is extended in order to take into account doping effects. The case of HF-doped ice is considered: it is shown that there is a strong accumulation effect of HF molecules in the dislocation cores, which induces an increase of the rate of transitions. The results are in agreement with experimental data concerning both the velocity of dislocations and high-temperature internal friction in HF-doped ice.
Bottom Crevasses
Authors: Weertman J.
Published: September 2017

An approximate calculation is made of the rate at which a bottom crevasse in a cold ice shelf or tabular iceberg can close shut by freezing of water and can creep open through the creep deformation of ice. In all but the thickest ice shelves and icebergs, those with a thickness greater than about 400 m, the freezing process is the more important mechanism if the ice is cold (< – 10°C). Consequently in a cold iceberg or ice shelf a bottom crevasse, once formed, will freeze shut.
Frequency of Major Avalanche Winters
Authors: Fitzharris B.B. , Schaerer P. A.
Published: September 2017

A 70-Year record has been compiled for avalanches affecting the Canadian Pacific Railway at Rogers Pass, British Columbia. Time series are presented for avalanche frequency, avalanche mass, and length of avalanche debris on the rail line for 26 avalanche paths as well as for winter snow-fall. Winters with the heaviest avalanche activity were 1971-72, 1934-35, 1919-20, 1932-33, and 1953-54. Time-series analysis indicates that the size of avalanches has decreased in recent decades. Spectral analysis shows avalanche activity to the similar to white noise but with a weak periodicity of about 18 years. An examination of the climatology of big avalanche winters reveals two distinct circulation patterns: a strong zonal flow with frequent Pacific storms and heavy snow-fall; or a pronounced meridional flow, Arctic air outbreaks, and catastrophic avalanching released by rapid advection of warm moist Pacific air. Major avalanche winters need not be big snow-fall winters.
The Fundamental Processes in Conventional Alavalanche Forecasting
Authors: LaChapelle Edward R.
Published: September 2017

Conventional avalanche forecasting is practiced as a mix of deterministic treatment for snow and weather parameters and inductive logic to reach actual forecast decisions. Inductive logic of the scientific method dominates, making frequent use of iteration and redundancy to minimize decision uncertainties. The mental processes involved are holistic rather than analytical. Elementary information theory can be used rationally to sort data categories for minimum entropy and optimize inductive reasoning. Recognizing these principles affords a chance to improve the practice and teaching of conventional forecasting techniques.
Snow-Slab Studies at Whistler Mountain, British Columbia, Canada
Authors: Stethem C. , Perla R.
Published: September 2017

A study of 30 slab avalanches at Whistler Mountain ski area, British Columbia, indicates that slab instability initiates with highest frequency on 40° slopes, that the temperature at the slab bed surface is about –5°C averaged for the 30 cases, and that on the average the slabs have a snow density of about 220 kg/m3. These results agree well with results from earlier studies. A rich variety of crystals appear in photomicrographs of samples extracted from the bed surfaces of the 30 slabs. In many cases, crystals extracted from the plane of critical weakness do not differ markedly from crystals extracted from adjacent strata.
Avalanche Education for Skiers
Authors: Valla François
Published: September 2017

The numbers of people rambling in the mountains is increasing every day. Consequently, the number of avalanche accidents is very significant. In France, the main mountain users organizations, headed by ANENA, work for a better education of those in the mountains. Various aspects of training courses and public information services are discussed.
A Fragment–Flow Model of Dry–Snow Avalanches
Authors: Mears Arthur I.
Published: September 2017

Field data on dry–slab avalanches obtained during the period 1975–79 from several snow climates suggest the following: (1) most of the mass of the typical avalanche studied consisted of fragments with lengths greater than 5 cm, (2) transverse and longitudinal shear planes formed during deceleration in the avalanche run–out zone, and (3) the flow height exceeded the slab height in most cases. No correlation was found between the run–out distance and the track or run–out zone slope, or between the run–out distance and the released slab height.

The field data suggest that avalanche motion is best described as a flow of fragments in which boundary shearing stresses are sensitive to fragment size distributions and volumetric solids concentrations. These factors may be more important than the roughness of the avalanche boundary in determining maximum velocity and run–out distance.
Seismic and Impact–Pressure Monitoring of Flowing Avalanches
Authors: Schaerer P. A. , Salway A. A.
Published: September 2017

Continuous records have been made during the passage of dry–snow avalanches of both seismic signals, which allows the avalanche speed to be estimated, and impact pressures on load cells with surface areas of 645 and 6 450 mm2. The impact pressure recordings show an initial peak followed by a base pressure. The observed initial and base pressures vary strongly within avalanches and from one avalanche to another, but, on average, they can be correlated with the frontal speed and the density of the deposited avalanche snow. It is concluded that well–developed dry–snow avalanches have an unsteady wave motion similar to the slug flow observed in ultra–rapid flow of water, and that they consist of three stratified components: dense flowing snow at the bottom, light flowing snow, and powder snow.
A Two–Parameter Model of Snow–Avalanche Motion
Authors: Perla R. , Cheng T. T. , McClung D.M.
Published: September 2017

Voellmy’s (1955) method for computing the run-out distance of a snow avalanche includes an unsatisfactory feature: the a priori selection of a midslope reference where the avalanche is assumed to begin decelerating from a computed steady velocity. There is no objective criterion for selecting this reference, and yet the choice critically determines the computed stopping position of the avalanche. As an alternative, a differential equation is derived in this paper on the premise that the only logical reference is the starting position of the avalanche. The equation is solved numerically for paths of complex geometry. Solutions are based on two parameters: a coefficient of friction μ; and a ratio of avalanche mass–to–drag, M⁄D. These are analogous to the two parameters in Voellmy’s model, μ and ξH. Velocity and run-out distance data are needed to estimate μ and M⁄D to useful precision. The mathematical properties of two–parameter models are explored, and it is shown that some difficulties arise since similar results are predicted by dissimilar pairs of μ and M⁄D.
An analysis of compressive strain in adjacent temperature-gradient and equi-temperature layers in a natural snow cover
Authors: Armstrong Richard L.
Published: September 2017

Compressive strain-rates in discrete layers of a sub-alpine snow cover are analyzed. Individual layers are identified according to density and the dominant type of metamorphism which contributed to their formation. Data were collected during four winter seasons at the Institute of Arctic and Alpine Research (INSTAAR) snow-study site (3 400 m), Red Mountain Pass, south-western Colorado, U.S.A. At average densities of less than 250 kg m₋3 the influence of metamorphism on strain-rate is not apparent. However, at densities greater than 250 kg m₋3, two separate relationships emerge for strain as a function of crystal type and density. While two adjacent layers may exhibit comparable densities, a layer of sintered, fine grained (ET) snow indicates a strain-rate approximately one order of magnitude greater than an adjacent layer of cohesionless, coarse-grained (TG) snow.
Thermodynamics of snow metamorphism due to variations in curvature
Authors: Colbeck S. C.
Published: September 2017

In the absence of imposed temperature gradients, the metamorphism of dry snow is dominated by the slow process of vapor diffusion between surfaces of different radii of curvature. This process is so slow in a seasonal snow cover (where temperatures normally change on the scale of hours or days) that vapor migration is usually dominated by the imposed temperature gradient. Thus radius of curvature contributes to but does not control metamorphism except for short periods in very fresh snow. As opposed to dry snow, liquid-saturated snow (i.e. pore space filled by the melt) is metamorphosed by heat flow arising from relatively large temperature differences among the particles. Grain growth in liquid-saturated snow is rapid because of the large temperature differences at nearly constant liquid pressure. In wet snow with low liquid content (2-5% by volume), grain growth is dominated by vapor diffusion (as in dry snow) so grain growth is much slower than under conditions of liquid saturation.
Avalanche Zoning in France –Regulation and Technical Bases
Authors: Crécy L. de
Published: September 2017

Avalanche zoning in France comprises two main parts:

1. A map of the probable location of avalanches was produced between 1970 and 1976, at a scale of 1 : 20000, and covering nearly 600000 ha. This was prepared by using a novel method based on:

(i)

the photo-interpretation of air photographs: the relief, extent of vegetation, notably forests the structure of deposits and alluvia, the comparison of several areas, thus enabling the zones …. which appear to have been struck by avalanches in the past to be identified;

(ii)

information acquired from inhabitants and the study of archives;

(iii)

a detailed inspection of the ground which can reveal physical or anthropogenic signs not disclosed by photo-interpretation.

This map is only concerned with the past and gives no indication of frequencies.

2. French law places an obligation on the State to define the limits of the zone subject to natural risk betore a building permit can be obtained.

Consequently, since 1974 when France ventured into zoning, plans have been made on a large scale (1 : 2000) showing the zones exposed to avalanches. Plans are made in three colours: white presumed to be without danger, red dangerous and therefore prohibited to constructors, and blue zones, doubtful.

Blue zoning, the most difficult to establish, relics on the evaluation of specialists, supported by the classical calculation of Voellmy, as well as by some first results received from experiments in a water channel for powder-snow avalanches, or from numerical simulations for other avalanches.

The blue zone includes heavy avalanches with a time of return greater than 300 years and slightly more frequent avalanches (return time 30-50 years) but of very little importance.

According to circumstances in every blue zone, several types of measure are recommended: police measures (evacuation or regulation in the home), architectural measures of reinforcement protective structure construction or annual checking by the authorities that natural (forest) or artificial (structures) defences are in a good state.
Snow Avalanche Hazard Zoning in British Columbia, Canada
Authors: Freer G. L. , Schaerer P. A.
Published: September 2017

Many developed areas in British Columbia are exposed to snow-avalanche hazards. Avalanche-hazard zoning has been undertaken by the British Columbia Ministry of Transportation, Communications, and Highways during the past five years. Recommendations from these zoning studies are forwarded to those agencies responsible for land-use zoning and development approval. Existing and possible legislation are described, as well as problems associated with implementation of the legislation. Technical considerations are outlined; interpretation of vegetation is a very important factor in evaluating each avalanche site. Calculation of run-out distances and consideration of other factors serve as a check on the vegetation interpretation. A special safety factor has been developed.

Socio-political considerations with respect to British Columbia are described. Existing developments have the most wide-ranging implications.
Avalanche zoning in alaska, U.S.A.
Authors: Hackett Steve W. , Santeford Henry S.
Published: September 2017

Over 30% of Alaska’s 586 400 squares miles (1 518900 km2) is subject to snow-avalanche activity. For a state-wide avalanche hazard evaluation, Alaska has been divided into six major snow— avalanche regions on the basis of topography, climatological data, dominant snow—pack conditions, and typical avalanche activity. They are: Arctic Slope, Brooks Range, Western, Interior, South—central, and South—east.

Mountainous terrain was studied at scales of 1 : 250 000 and 1 : 1 584000; final compilation was at a scale of 1 : 2 500 000. Regional snow—pack and climatic conditions were cross—correlated with relief zonation of each avalanche region to produce a map of Alaska's provisional snow—avalanche potential.

Most of the mountainous areas in the South—central and South—east regions, because of their northern latitude, closeness to large masses of water, and large orographic and cylonic weather processes, are susceptible to major avalanche activity. For areas near population centers, the potential avalanche terrain has been identified from data on known and suspected avalanche activity through air photographs, terrain analysis, and documented snow—avalanche occurrences compiled at scales of 1 : 250 000 and 1 : 63 360.

The state—wide regional data compilation and study are initial steps toward avalanche zoning in Alaska. Local land—use planning and detailed investigations are needed to establish effective natural—hazard zoning in municipal areas as related to snow avalanche activity.
Drifting-Snow Similitude—Transport-Rate and Roughness Modeling
Authors: Iversen J. D.
Published: September 2017

This paper reports on results from a series of experiments in a boundary-layer wind tunnel concerning snow-drift control adjacent to grade separations on interstate highways. A new application of similitude principles making use of theoretical relationships involving drifting particulate material is presented. The primary modeling parameters are considered to be a mass-rate parameter and an aerodynamic roughness parameter. They are derived by considerations of mass-transport rate of material in saltation and the equivalent roughness height of material in saltation. The parameters are combined empirically to correlate model snow-drift data successfully as well as to predict equivalent full-scale wind speeds and storm durations. The combined parameter has been used to compare and evaluate a variety of drift-control techniques adjacent to an interstate highway grade-separation crossing.
Geometry and Density of Drifts Formed by Snow Fences
Authors: Tabler Ronald D.
Published: September 2017

This paper presents results from studies of snow-drifts formed by vertical-slat “Canadian” and horizontal-slat “Wyoming” snow fences having 50% porosity and heights H from 0.8 to 3.8 m, on nearly level terrain. Characteristics of equilibrium lee drifts behind the Wyoming fence include cross-sectional area 19.3H 2, length 30H, maximum depth 1.20H. and water-equivalent volume 6.8H 2.18. Up-wind drift dimensions include maximum depth 0.5H and length 12H. Drifts behind Canadian fences are about 25% smaller than for the Wyoming design. Polynomial regression equations are fitted to drift profiles for both fence types. Relationships are presented for the effects of wind orientation and curvature of drifts near fence ends, as well as empirical equations describing pre-equilibrium geometry relative to degree of saturation. Mean density ρ (kg/m3) of drifted snow having depth y (m), is given by ρ = 376+158 log y.
Self-Similarity of Wind Profiles in Blowing Snow Allows Outdoor Modeling
Authors: Tabler Ronald D.
Published: September 2017

Drifts formed by snow fences appear to be scaled in proportion to fence height over a height range of nearly two orders of magnitude. This paper examines natural scaling in terms of commonly accepted similitude criteria. It is suggested that requirements for dynamic similarity of flow fields are satisfied over a period of time because surface roughness heightz0varies approximately as the square of shear velocityu⋆2for saltating flows in air. This is demonstrated by intensive measurements of wind profiles over snow and ice surfaces. Satisfaction of similitude requirements for scaling particle motion is less certain, although natural sorting may effectively scale particles over a restricted range of wind speeds. Natural scaling of drifts suggests snow erosion and deposition can be studied with reduced-scale models on smooth surfaces outdoors. The feasibility of this technique is demonstrated by results from 1 : 30 scale models of 1.8 and 3.8 m snow fences on both level lake ice and irregular terrain constructed from compacted snow.
A Slip-velocity Hypothesis Applied to Hydraulically Smooth Wind Flow Over a Snow cover
Authors: Bergen James D.
Published: September 2017

An hypothesis relating the slip velocity for laminar flow over a porous surface to the specific permeability of the surface proposed by Beavers and Joseph (1967) is applied to the problem of estimating the surface shear stress on an extensive snow surface at low wind speeds. Vertical profiles of wind speed and the air permeability of the surface snow layer were recorded for five periods of neutrally stable, hydraulically smooth flow. The variation of the ratio of the slip velocity to the surface shear stress with the specific permability was examined. The data are compatible with the hypothesis, although they are too sparse to allow valid estimates of the coefficients in the hypothesis.
Threshold Wind-Speeds and Elastic Impact in Snow Transport
Authors: Schmidt R. A.
Published: September 2017

Cohesive forces are added to the analysis of forces on sand and soil particles to show that fluid drag, alone, often cannot initiate movement of a snow surface. The impact force of saltating ice spheres, however, can easily provide the force to break cohesive bonds, according to these calculations. The argument suggests a balance between the distribution of bond strengths of exposed surface particles and the distribution of saltation trajectory heights.
Snow Transport Over Mountain Crests
Authors: Föhn Paul M. B.
Published: September 2017

In order to gain more insight into the mountain snow-transport mechanisms wind and drift flux measurements have been executed on a ridge crest (mainly during snow-storms). Horizontal wind-speed profiles, measured between 0.3 and 6 m above snow surface, show a hump-shaped course especially for strong winds. Theoretical approximations substantiate that the Bernoullian pressure decrease on the crest may be the main cause for this type of wind profile. Roughness parameters (Z0, u⋆) are determined with the aid of the wind profiles and compared with those reported in the literature. Corresponding drift density profiles coincide with steady-state drift theories as long as wind speeds are low (u1≤ 7-10 m s-1), at greater wind speeds snow plumes of 1 to 1.5 m thickness develop immediately above snow surface. Areal measurements on snow mass-balance differences between windward and lee slopes are used to approximate the total transport over the ridge crest and to derive a quantitative relationship between crest winds and drift-snow deposition on lee slopes.
The Energy-Line Method in the Mechanics of avalanches
Authors: Körner H. J.
Published: September 2017

The energy-line method results from the graphical representation of the energy law as applied in hydraulics. It makes it easier to understand the entire process of the movement of an avalanche from where it breaks away to where it is deposited. The technique, the energy lines, and the average slope of avalanches, as well as the theoretical energy lines of the one-coefficient and two-coefficient models of avalanche dynamics, are described. The method is explained by means of an example.
Snow–Pack Structure: Stability Analyzed by Pattern–Recognition Techniques
Authors: LaChapelle Edward R. , Ferguson Sue A.
Published: September 2017

Internal snow–cover structure depicted by conventional snow profiles is commonly held to be important for avalanche forecasting but it is largely omitted from numerical forecasting schemes owing to quantification difficulties. A subjective test given to practising forecasters illustrated the complex roles of measured profile parameters in describing instability. A clustering technique of pattern recognition, after introducing a snow–profile training set, has demonstrated an objective ability to sort correctly 86% of the layer boundaries associated with slab–avalanche bed surfaces or lubricating layers. Further improvement in stability recognition comes from a newly devised shear test driven by a wedge which quickly locates failure planes within the snow cover. The cluster analysis is then able to sort with similar accuracy between stable and unstable (avalanching) failure planes so located.
The Avalanches of December 1966 in Western T’ien-shan, China
Authors: Jiaqi Qiu , Ruji Hu
Published: September 2017

The exceptional avalanches of December 1966 in the basins of the Gunes and Kashi Rivers caused much damage and blocked the highway for several months. The general avalanche conditions in this area and the exceptional weather which caused the exceptional avalanches are described.
Recent Progress and New Applications of the Dynamics of Avalanches
Authors: Brugnot Gerard
Published: September 2017

This paper reports the present stage in our research programme. We have used two very different models : (i) A numerical model treating the avalanche as a Newtonian liquid with a free surface; this model describes qualitatively the velocity fluctuations both of avalanche particles and of the front and gives some quantitative predictions, but much experimentation is needed to determine the large number of parameters involved. (ii) An analogue model in which powder avalanches have been simulated in an underground tunnel, taking account of the densimetric Froude number; this model reproduces the pressure rise which precedes the visible front, and also the pressure wave as the front passes which causes so much damage to engineering works—and human beings. These models have been applied to two cases—a bridge and a snow shed.

The interplay between models and experimentation is discussed and the need for improved data on the mass output of an avalanche, of its detailed velocity history, and of the force on large objects is emphasized. Methods being used to try to supply this information are discussed ; gamma-ray measurements for specific mass, high-speed stereophotogrammetry for velocity, and various pressure sensors for the force. The possibility of releasing real powder avalanches to enable such measurements to be made more reliably is being investigated.
Topographical effects of Snow Deposition on Restructured Land
Authors: Chaco E. , Molnau M.
Published: September 2017

The measurement of snow accumulation and distribution is one of the primary objectives of a study on the melt of snow-drifts and erosion in the phosphate mining region of south-eastern Idaho. The study area is located in an active phosphate mine and is limited to the sites of waste dumps, a product of the surface mining technique used in this area. Four sites are included in the overall study with one dump selected for intensive snow measurement. Snow deposition data have been collected for one winter season (November 1977—June 1978) on a grid pattern over this dump. The area of the study site has been expanded and similar measurements are planned for the coming snow season.

The snow measurements were made monthly on a pre-established 23 m (75 ft) square grid overlaid on the dump. The analysis of the snow data consists of contour mapping of any one or all the snow properties measured—snow depth, density, or water equivalent. In addition, since the measurements are made on the same grid each month, mathematical manipulation of grid data allows contour maps of the residual of the monthly snow properties to be plotted. A similar analysis of terrain properties collected on the same grid results in contour maps displaying ground slope, concavity-convexity of the surface, aspect, or distance from snow- deposition obstacles.

The aim of the analysis using these types of data is to arrive at a model which will compute patterns of snow accumulation and distribution on the ground surface given a description of terrain type and probable meteorological properties of the region. A preliminary comparison of the maps shows a similar pattern of snow deposition occurring each month with the exposed areas of the dump swept clean and the greatest snow depth occurring in the sheltered concavities.
A Preliminary System to Predict Snow Instability using Acoustic Emissions
Authors: Sommerfeld R. A.
Published: September 2017

Results From the last four winters’ studies on acoustic emissions from snow slopes have shown that periods of higher noise in the frequency band 5 to 125 Hz are associated with periods of instability, but that the phenomenon of acoustic emissions from unstable snow is very weak. Interference with the acoustic emissions from extraneous sources such as chairlifts, trucks, and airplanes causes ambiguities in the data which interfere with the straightforward prediction of instability.

Spectra of the noises were examined, with the idea that filters might improve the signal-to-noise ratio. It was found that the noise generated by unstable snow can occur over a fairly wide range of frequencies and that there is no band of frequencies which is unique to unstable snow. It was found that the noise from the chairlift had a very stable spectrum and that it had a band from 50 to 65 Hz which was pronounced and in which the snow noise was fairly low. The r.m.s. voltage in the band 5 to 125 Hz can therefore be reduced by subtracting a proportion of the r.m.s. output of a narrow-band 55 Hz filter. By adjusting the constant of proportionality, it was possible to eliminate interference from the chairlift almost entirely, and this will be used.

Spectral analyses have also shown that ambiguities are generated by variations in the 60 Hz power-line noise. It is possible to suppress this with the use of filters, but without complex digital data manipulation, it is not possible to eliminate it.

The fact that the snow noise does not transmit over large distances means that events of interest should not occur simultaneously on two, widely spaced geophones. The system will include a geophone in an unstressed region whose r.m.s. voltage will be subtracted from that of the geophone in the stressed region to eliminate signals which are common to both. It is hoped that this technique will eliminate ambiguities caused by extraneous sources such as trucks and airplanes.
Prevention of Avalanches in the Gunes Valley in T’ien-Shan, China
Authors: Yanlong Wang , Zichu Xie , Zhizhong Zhang
Published: September 2017

A section of the highway through the Gunes valley can be seriously interrupted by avalanching; in 1966-67 traffic was interrupted for four months. About 86 places are threatened by avalanches, most of which are channelled avalanches that do not reach the highway every year.

A comprehensive programme to study the avalanches was begun in 1967 on the basis of which avalanche protective works were undertaken in 1974-75 and their effectiveness analysed in 1976-77. Most of these depend on local material; the main rock deposits available are andesite, which has good permeability and is very suitable for earthworks.

The most common type of defence used is the building of mounds, 4-6 m high, 10-12 m wide, and 20-30 m long with a ditch dug in front. Such mounds have the effect of braking the avalanche flow and also of capturing snow on the uphill side. A second system is the terracing of slopes; beginning from the avalanche fracture line, earth is dug parallel to the contours. In two places dykes have been built to guide the snow, and in a few places avalanche sheds have been constructed, though because of expense these have been kept to a minimum. As the soil and climatic conditions are very suitable, tree planting around structures is a successful way of increasing avalanche protection.

During the analysis of effectiveness snow-fall as recorded was heavy, but the defences were effective and avalanches did not seriously interrupt the highway.
Tectonic processes in Svalbard tide-water glacier surges: evidence from structural glaciology
Authors: Richard Hodgkins , Dowdeswell Julian A.
Published: September 2017

The tectonic effects of a glacier surge differ from those of steady state because flow is driven by longitudinal stresses rather than shear stresses. The orientations of recently formed crevasses, indicating the directions of the principal stresses, have been used to investigate tectonic processes in glacier surges recorded by repeat aerial photography. Long-term, large-magnitude shifts in stress regime are demonstrated, as are short-term propagation features. Two types of tide-water glacier advance are identified, depending on the position of the surge front relative to a low effective-pressure zone at the glacier terminus.
Ice Flow along the Byrd Station Strain Network, Antarctica
Authors: Whillans I. M.
Published: September 2017

The flow of the Antarctic ice sheet near Byrd Station is modeled using surface net accumulation-rate data, surface strain-rate data, and core-hole tilting results. The model empirically allows for the progressive development of ice fabric and for values of the vertical strain-rate nearer to zero at depth, and adjusts the strain-rates according to the effect of the climatic warming at the beginning of the Holocene.

The validity of the model is supported by the agreements between calculated bed form and that measured by radar sounding, and between calculated and measured present-day ice-sheet thinning-rates. The ice was about 200 m thicker before thinning.

The depth-age relationship for the Byrd Station ice core shows that the climatic change represented by the oxygen isotopic ratio of the ice began some 5000 years sooner than in north Greenland (Hammer and others 1978), but ended at about the same time.