bluuebunny/crossref_metadata_2025 huggingface dataset:
Radio and Electrical Measurements on Glacial Streams
Authors: Walford M. E. R.
Published: September 2017

We discuss the suggestion that small underwater transmitters might be used to illuminate the interior of major englacial water channels with radio waves. Once launched, the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss. Receivers placed within the channels or at the glacier surface could be used to detect the signals. They would provide valuable information about the connectivity of the water system. The electrical conductivity of the water is of crucial importance. A surface stream on Storglaciären, in Sweden, was found, using a low-frequency technique, to have a conductivity of approximately 4 × 10−4 S m−1. Although this is several hundred times higher than the conductivity of the surrounding glacier ice, the contrast is not sufficient to permit us simply to use electrical conductivity measurements to establish the connectivity of englacial water channels. However, the water conductivity is sufficiently small that, under favourable circumstances, radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel. In a preliminary field experiment, we demonstrated semi quantitatively that radio waves do indeed propagate as expected, at least in surface streams. We conclude that under-water radio transmitters could be of real practical value in the study of the englacial water system, provided that sufficiently robust devices can be constructed. In a subglacial channel, however, we expect the radio range would be much smaller, the environment much harsher, and the technique of less practical value.
A Digital Technique to Estimate Polynya Characteristics from Synthetic Aperture Radar Sea-Ice Data
Authors: Lyden James D. , Shuchman Robert A.
Published: September 2017

A new technique has been developed to estimate digitally the concentration and structure of open-water leads (polynyas) in synthetic aperture radar (SAR) sea-ice data. This procedure consists of smoothing the original SAR sea-ice data to reduce speckle effects, level slicing this smoothed image to produce a binary image consisting of ice and open water, generating the autocorrelation function of this image, and interpreting the autocorrelation function for lead information. Preliminary results indicate that this technique yields useful estimates of lead characteristics, but that additional research is required to evaluate fully its performance.
Sliding with Cavity Formation
Authors: Fowler A. C.
Published: September 2017

We present a model for the determination of a sliding law in the presence of subglacial cavitation. This law determines the basal stress at a clean ice‒bedrock interface in terms of the velocity and effective pressure. The method is based on an exact solution of the Nye—Kamb (linearly viscous) sliding problem with cavities, and uses ideas of Lliboutry (1979) to construct, via renormalization methods, an approximate law for general bedrock form. We show that, for a bedrock whose spectrum has a power‒law behaviour, one obtains a sliding law which gives the basal shear stress proportional to a power of the velocity, and to a power of the effective pressure.

The effect of subglacial cavitation on the drainage system is examined, using recent ideas of Kamb. For sufficiently high velocities, drainage through a Röthlisberger tunnel system is unstable, and drainage takes place through the linked system of cavities. This leads to a reduction of the effective pressure, and by taking account of this, one can rewrite the sliding law in terms of stress and velocity only.

This sliding law can be multi‒valued, and it is suggested that this underlies the dynamic phenomenon of surges.
On the Significance of Normal Stress Effects in the Flow of Glaciers
Authors: Man Chi-Sing , Sun Quan-Xin
Published: September 2017

McTigue and others (1985) identified a possible problem in the type of constitutive equation usually used for modeling the creep behaviour of polycrystalline ice. They pointed out that Glen’s flow law necessarily excludes the consideration of normal stress effects, which are of great significance in other disciplines that consider non-Newtonian fluids. Using the second-order fluid (with material parameters evaluated from laboratory data) as a tentative model for ice, they reached the conclusion that normal stress effects may be discernible in natural glacier flow. But, as noted by McTigue and others, the second-order fluid “fails to represent the non-linear rate dependence of ice in shear”; therefore it is in fact not a suitable constitutive model for glacier ice in shearing flow. In this note, parallel to what McTigue and others did for the second-order fluid, we present a similar analysis for (I) the modified second-order fluid and (II) the power-law fluid of grade 2, both of which are constitutive models recently proposed by Man as a tentative generalization of Glen’s flow law. Both models (I) and (II) can represent normal stress effects, and both agree with Glen’s flow law in the prediction of the depth profile of velocity in the steady laminar flow of glaciers. For ease of comparison, the same creep data of McTigue and others are used in quantifying the material parameters in these two models. Both models (I) and (II) predict far less pronounced normal stress effects in glaciers than those estimated by McTigue and others (whose data analysis in fact suffered from inconsistencies and over-parameterization).
Glacier Flow in a Curving Channel
Authors: Echelmeyer Keith , Barclay Kamb
Published: September 2017

The flow of a glacier along a channel of constant longitudinal curvature is analyzed using analytical and finite-element methods. Channels of various cross–sectional shape are investigated, ranging from a simple rectangular form with zero shear traction along the bed to realistic profiles taken from Blue Glacier, Washington. Terms in the equilibrium and rate-of-deformation equations which are inversely dependent on radius and a body force which varies transversely across the glacier introduce several characteristic features into the stress and velocity fields of the curving glacier. The stress center line is shifted toward the inside of the bend, causing an asymmetric crevasse pattern and non‒zero stress magnitude at the surface on the geometric center line of the channel. The stress field is dependent on the stress exponent in the flow law and is non-linear across the surface. The surface–velocity pattern shows a “tilting” of the usual high‒order parabolic form, being skewed toward the inside of the bend. There is a shift in the velocity maximum from the deepest part of the channel. All of these curvature‒induced features are dependent on the radius of curvature, actual channel geometry, and stress exponent in the flow law. Model results show excellent agreement with the velocity and crevasse patterns on the curving Blue Glacier.
Stable Isotopes and Debris in Basal Glacier Ice, South Georgia, Southern Ocean
Authors: Sugden David E. , Clapperton Chalmers M. , Campbell Gemmell J. , Knight Peter G.
Published: September 2017

This paper combines a study of the rock debris and δD/δ18O isotopic characteristics of basal ice sequences in three representative glaciers in South Georgia and concludes that the debris and ice has been entrained mainly by basal freezing. The size distribution of the rock debris is typical of crushing and abrasion, and reflects transport at the ice–rock interface. The δD/δ18O relationships show that clear ice associated with the debris has accreted through freezing. The white bubbly glacier ice has δD/δ18O relationships typical of precipitation which demonstrates an altitudinal effect between glaciers.
A Stress–Strain Relation for Dry Snow in Greenland and Antarctica
Authors: Ling Chi-Hai , Rasmussen L.A. , Benson Carl S.
Published: September 2017

A stress–strain relation for dry snow in Greenland and Antarctica was derived. When this relation is integrated, it gives snow density as a function of time. For given surface density, temperature, and accumulation, the age of snow layers can be obtained as a function of depth in the snow-pack. Calculations compare well with observations. With some knowledge of the temperature range in the upper layer of the snow-pack, calculation for density versus depth can also be improved over the results where such temperature information was not used.
Intensity of Satellite Radar-Altimeter Return Power Over Continental Ice: A Potential Measurement of Katabatic Wind Intensity
Authors: Remy F. , Brossier C. , Minster J.F.
Published: September 2017

We analyse, above continental ice, the various factors which affect the power return of the Seasat radar altimeter as measured by its Automatic Gain Control (AGC). Corrections of effects due to the AGC loop control are first applied. AGC is then normalized by positioning the half-power point at the middle of the instrument receiving window. This operation is valid for both surface and volume scattering. Over a part of Antarctica between long. 90° and 150°E., the remaining variations of AGC are of the order of 15 dB. Most of these variations occur on a large scale (>100km) and are correlated with the katabatic wind intensity. This indicates that AGC measures either surface roughness of the ice, which is related to wind intensity, or grain-size which could also be dependent on the wind. In-situ measurements support the evidence that the radar altimeter is more sensitive to surface scattering. These data could therefore provide a measurement of the intensity of katabatic winds over the continental ice.
A Surge of Bualtar Glacier, Karakoram Range, Pakistan: A Possible Landslide Trigger
Authors: Gardner James S. , Hewitt Kenneth
Published: September 2017

Bualtar Glacier, Karakoram Range, northern Pakistan, surged during the spring and early summer of 1987. This followed a major episode of three landslides which impacted part of the glacier ablation zone on 30–31 July 1986. In May 1987, surface velocities of 7 m d−1 were measured at one profile down-glacier from the landslide deposits, where in 1986 velocities were an order of magnitude less. Surface and hydrological characteristics of the glacier in and down-glacier from the landslide deposit were also indicative of surge-like behavior in 1987, and a return to pre-surge conditions by 1988.
The Potential for Basal Melting Under Summit, Greenland
Authors: Firestone John , Waddington ED. , Cunningham James
Published: September 2017

The deep-drilling projects at the Summit ice divide will require thermal models to help interpret the paleoclimatic signals in their cores. An analytic, steady-state model predicts basal temperatures within 1 °C of the ice melting-point and basal ice no older than 100–400 kyear should melting occur. A two-dimensional, time-dependent temperature model includes the effects of realistic two-dimensional ice flow and the temperature and mass-balance patterns of the last two glacial cycles. The model relaxes some assumptions made in one-dimensional studies and produces lower basal temperatures. The basal temperatures are most sensitive to the value of the geothermal heat flux and the mass-balance pattern. If the flux is less than 56 mW m−2, the bed has likely been frozen throughout the last glacial cycle. The decoupling of the energy and mass-conservation equations is a significant source of error which can be eliminated only by a fully coupled ice-flow/ heat-flow model.
A Theoretical Determination of the Characteristic Equation of Snow in the Pendular Regime
Authors: Morris E.M. , Kelly R.J.
Published: September 2017

Recent mathematical models treat a natural snow-pack as a mixture body consisting of solid ice grains, liquid water, and a gas made up of air and water vapour. Such a model requires two independent constitutive equations for the two independent volume fractions. However, so far only one equation, a power law relating the liquid-water content to capillary pressure, has been suggested, by analogy with the so-called “characteristic” equation for liquid water in soils. Experimental data from drainage tests on snow columns may be used to determine the characteristic equation for snow for relatively high water contents. However, the experimental method is not valid when water exists in isolated inclusions in the snow, i.e. in the pendular regime. In this paper a theoretical method is used to derive two independent volume-fraction laws for snow in the pendular regime.
A Model for Scaling Avalanche Speeds
Authors: Mcclung D.M.
Published: September 2017

Snow-avalanche speeds, run-out distances, and the concepts from dense granular flows are combined in a model for prediction of speeds along the incline. Field measurements indicate that speeds and run-out distances are nearly independent of path steepness once a length is chosen to scale them. Application of granular-flow concepts explains these results. The most important feature of the model (and the speed data) is the steep gradient of speeds in the run-out zone. These results emphasize the need for high precision in run-out prediction when construction or defences are contemplated.
On the Temperature Distribution of Glaciers in China
Authors: Maohuan Huang
Published: September 2017

To date, the temperatures of 22 glaciers in China have been measured. It is suggested that the minimum temperature at the base of the active layer in the upper part of the ablation area (Tmin) be used as a characteristic temperature and compared with mean annual air temperature (Ta). The temperature distribution is discussed for various glaciers. Polar-type glaciers are characterized by low temperatures with Tmin < −10°C, Tmin close to Tv and a cold base in general; sub-polar-type glaciers with −10°C < Tmin < −1.0°C, Tmin higher than Tv and a melting base are usually located beneath the middle of the ablation area; and temperate-type glaciers with Tmin < −1.0°C, certainly higher than Ta and a sub-freezing near-surface layer in the ablation area all the year round, because the snow cover is thinner in winter.
Response of the Energy Balance on the Margin of the Greenland Ice Sheet to Temperature Changes
Authors: Braithwaite Roger J. , Olesen Ole B.
Published: September 2017

Daily ice ablation on two outlet glaciers from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), is related to air temperature by a linear regression equation. Analysis of this ablation-temperature equation with the help of a simple energy-balance model shows that sensible-heat flux has the greatest temperature response and accounts for about one-half of the temperature response of ablation. Net radiation accounts for about one-quarter of the temperature response of ablation, and latent-heat flux and errors account for the remainder. The temperature response of sensible-heat flux at QQamanârssûp sermia is greater than at Nordbogletscher mainly due to higher average wind speeds. The association of high winds with high temperatures during Föhn events further increases sensible-heat flux. The energy-balance model shows that ablation from a snow surface is only about half that from an ice surface at the same air temperature.
A Simple Energy-Balance Model to Calculate Ice Ablation at the Margin of the Greenland Ice Sheet
Authors: Braithwaite Roger J. , Olesen Ole Β.
Published: September 2017

Data for daily ice ablation on two outlets from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), are used to test a simple energy-balance model which calculates ablation from climate data. The mean errors of the model are only −1.1 and −1.3 mm water d−1 for Nordbogletscher (14 months) and Qamanârssûp sermia (21 months), respectively, with standard deviations of ±13.6 and ±18.9 mm water d−1 for calculating daily ablation. The larger error for Qamanârssûp sermia may be due to variations in ice albedo but the model also underestimates ablation during Föhn events.

According to the model, radiation accounts for about two-thirds of mean ablation for June-August at the two sites, while turbulent fluxes account for about one-third. The average ablation rate is higher at Qamanârssûp sermia than at Nordbogletscher because both sensible-heat flux and short-wave radiation are higher.
Numerical Simulation of Powder-Snow Avalanches
Authors: Fukushima Yusuke , Parker Gary
Published: September 2017

Appropriate expressions describing the motion of powder-snow avalanches are derived. The model consists of four equations, i.e. the conservation equations of fluid mass, snow-particle mass, momentum of the cloud, and kinetic energy of the turbulence. Insofar as the density difference between the avalanche and the ambient air becomes rather large compared with the density of the ambient air, the Boussinesq approximation, which is typically used to analyze density currents, cannot be adopted in the present case. As opposed to previous models, the total buoyancy of a powder-snow avalanche is allowed to change freely via erosion from and deposition on to a static snow layer on a slope. In the model, the snow-particle entrainment rate from the slope is directly linked to the level of turbulence.

A discontinuous, large-scale powder-snow avalanche occurred on 26 January 1986 near Maseguchi, Niigata Prefecture, Japan. The avalanche appears to have had a dense core at its base. The present model is employed to simulate that part of the avalanche above any dense core. The depth of the layer of fresh snow is considered to be an important parameter in the model. The larger the depth of fresh snow, the larger is the concentration of snow attained in the avalanche, and the faster its speed. It is seen that the model provides a reasonable description of the powder-snow avalanche generated near Maseguchi. In particular, the model prediction that a powder-snow avalanche strong enough to reach Maseguchi requires a depth of fresh snow of at least 2 m is in agreement with the observed depth just before the event.
Analysis and Modeling of Melt-Water Refreezing in Dry Snow
Authors: Tad Pfeffer W. , Illangasekare Tissa H. , Meier Mark F.
Published: September 2017

A dynamic zone of thermal disequilibrium is described which separates wet snow at 0 ° C from dry, sub-freezing snow. The dynamic zone tends to be eliminated by thermal equilibrium through freezing, but is sustained and propagated into the sub-freezing snow by water flow from the wet snow. The width of the dynamic zone is controlled by the rate of water inflow, and by the rate of freezing of water on to sub-freezing ice grains, which is in turn controlled by the ice/water geometry. Two ice/water geometries are investigated: isolated ice spheres and capillary tubes of ice into which water is pulled by capillary suction. The rate of freezing of water is calculated for the two models for various initial dimensions and temperatures. Equilibrium times are short (typically about 0.5 s), but depend on the assumed geometry, which is poorly constrained by existing data. Equilibration times and freeze-on mass fluxes are calculated for a variety of general conditions. These results can be used in numerical models of wetting-front propagation into cold snow.
A PC-Based Portable Ice-Radar Receiver
Authors: Hammond W.R. , Sprenke K.F.
Published: September 2017

We have assembled a low-cost portable ice-radar receiver that is based on a personal computer (PC). The unit consists of a digital storage oscilloscope controlled by a lap-top PC. The total weight is 22 kg. The radar wave forms are digitized by the oscilloscope, displayed on the computer screen, and stored on a floppy diskette. All components are commercially available at a cost below $2000 U.S. The radar receiver has proved to be very versatile because the computing capabilities of an IBM-compatible PC are available in the field to control signal acquisition, to display radar wave forms in near-real time, and to perform sophisticated signal processing as measurements are taken. The PC-based ice-radar receiver was used for ice-thickness and bedrock power-reflection coefficient surveys of Mount Estelle glacier in the Alaska Range, Alaska, in 1988.
Ice deformation very close to the ice-sheet margin in West Greenland
Authors: Knight Peter G.
Published: September 2017

This paper describes fine-resolution measurements of glacier surface strain rates very close to the margin of Russell Glacier, West Greenland. Measurements at a small scale make possible detailed analysis of strain patterns close to the glacier margin, and suggest that strain rates vary over small areas. The strain pattern is determined by ice flexure over subglacial obstacles as well as by seasonally variable marginal retardation and by the orientation of the ice margin relative to the flow direction.
Temperature compensation of electrical conductivity in glacial meltwaters
Authors: Smart C. C.
Published: September 2017

Temperature compensation built into many conductivity meters becomes inaccurate in low-temperature waters typical of glacial melt streams. Experiments using simulated glacial waters show a linear dependence of electrical conductivity on temperature from 0.3° to 25°C. The slope of the temperature–conductivity relation is linearly dependent on the conductivity of the solution, allowing a numerical or analytical temperature correction to be made. To minimize error introduced by temperature compensation, measurements of electrical conductivity in glacial streams should be corrected to a low standard temperature, and 0°C is suggested.
A numerical model to simulate snow-cover stratigraphy for operational avalanche forecasting
Authors: Brun E. , David P. , Sudul M. , Brunot G.
Published: September 2017

Laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature, density and liquid-water profiles of snow cover as a function of weather conditions.

To establish these laws, the authors have summarized previous studies on temperature gradient and on wet-snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh-snow samples. An original formalism was developed to allow a description of snow with parameters evolving continuously throughout time.

The introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow-covered albedo, which depend on the simulated stratigraphy, i.e. the type and size of snow grains of different layers of the snow cover.

The model was tested during a whole winter season without any re-initialization. Comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail. The model proved itself to be very efficient in simulating accurately the evolution of the snow-cover stratigraphy throughout the whole winter season.
Microcracking and the failure of polycrystalline ice under triaxial compression
Authors: Kalifa P. , Ouillon G. , Duval P.
Published: September 2017

Triaxial and uniaxial compression tests have been carried out at –10°C on granular ice in order to study the role of microcracking on failure in the ductile-brittle transition zone. In the triaxial tests, the effect of confining pressure and strain rate on the crack population, as well as on strength and strain at the peak stress, was investigated. In the uniaxial tests, we measured the evolution of elastic and non-elastic components of deformation with the stress-strain history. The concept of effective stress, with a single scalar damage variable, was used to calculate the effect of microcracking on the strain components.
The role of bed separation and friction in sliding over an undeformable bed
Authors: Schweizer Jürg , Iken Almut
Published: September 2017

The classic sliding theories usually assume that the sliding motion occurs frictionlessly. However, basal ice is debris-laden and friction exists between the substratum and rock particles embedded in the basal ice. The influence of debris concentration on the sliding process is investigated. The actual conditions where certain types of friction apply are defined, the effect for the case of bed separation due to a subglacial water pressure is studied and consequences for the sliding law are formulated. The numerical modelling of the sliding of an ice mass over an undulating bed, including the effect of both the subglacial water pressure and the friction, is done by using the finite-clement method. Friction, seen as a reduction of the driving shear stress due to gravity, can be included in existing sliding laws which should contain the critical pressure as an important variable. An approximate functional relationship between the sliding velocity, the effective basal shear stress and the subglacial water pressure is given.
Non-linear acoustic imaging of ice properties
Authors: Guigné J. Y. , Crocker G. Β. , Hunt P.
Published: September 2017

Non-linear acoustic techniques have been used to investigate the properties of a pond-ice cover. The field tests showed that the position of the lower and upper surfaces, as well as some internal bubble layers, could be located with centimetre-scale resolution. These results are presented, along with an outline of parametric array theory and a description of the instrumentation. The data indicate that dynamic modelling of the acoustic response of ice will enable remote estimation of some of the bulk physical properties of the ice such as thickness, roughness and possibly brine volume. It follows that this approach to non-destructive imaging of ice properties may find application in a wide range of ice-engineering problems.
Subglacial floods and the origin of low-relief ice-sheet lobes
Authors: Shoemaker E. M.
Published: September 2017

The likely genesis of low-relief ice-sheet lobes is episodic subglacial floods which occur in the form of water sheets hundreds of kilometers wide. During the few weeks prior to termination, when the flood discharge is large, the average thickness of a water sheet beneath the Lake Michigan lobe likely exceeded 1 m and reached thicknesses in excess of 6 m. The release of a part of the basal shear stress during this period produced an elongation of the lobe of tens of kilometers.
Short-term variations in flow velocity of Glaciar Soler, Patagonia, Chile
Authors: Naruse Renji , Fukami Hiroshi , Aniya Masamu
Published: September 2017

Short-term variations in ice-flow velocity were obtained at intervals of a few hours and a few days in the ablation area of Glaciar Soler, Patagonia, Chile, in November 1985. A maximum flow rate was measured at about four times the minimum value. A good correlation, with a time lag of 7.5 h, was found between the ice-flow velocity in the lower reaches and the amount of water discharge from the glacier terminus. It was concluded, therefore, that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure.
Search for temporal changes in the velocity of Ice Stream B, West Antarctica
Authors: McDonald J. , Whillans I. M.
Published: September 2017

The position of the UpB camp on Ice Stream B, West Antarctica, has been measured 14 times during three field seasons. TRANSIT (doppler) satellite receivers were used. At the resolution of our measurements (2 m), no significant velocity variation was detected over time intervals ranging from 1 d to 2 years.
Theoretical analysis of snow-dam decay
Authors: Xia Zhaojun , Woo Ming-ko
Published: September 2017

Snow dams have been observed in many stream channels in the Arctic and the sub-Arctic, but there is no theoretical analysis of their decay processes. These processes include snowmelt, seepage erosion, down-cutting, snow-slope failure and flotation of the snow dam. Snowmelt can be determined by the energy balance. Seepage of water will cause serious erosion at the point where the stream or pond level in front of the dam intersects the dam face. Erosion by water overflowing the dam is due to down-cutting, under-cutting and thermal erosion. Down-cutting increases with discharge but decreases with the shear strength of the snow. Where a hydraulic jump occurs downstream of the dam, under-cutting can accelerate dam decay. Thermal erosion, depending mainly on water temperature, may be less significant than the previous two processes. Slope failure occurs when the driving forces exceed the resisting forces, and these are affected by snow property and snow load. When the stream or pond level downstream of the dam rises rapidly, the dam is prone to float. As peak flow often occurs during the break-up period, results of the theoretical study of the mechanisms of snow-dam decay will improve flood forecasting for Arctic streams.
Freezing Water and Supercooling: Anchor Ice and Frazil Ice
Authors: Devik Olaf
Published: September 2017

The supercooling of water in nature occurs more frequently than is generallyknown. It always takes place when still water is in process of being covered with thefirst ice needles. It is of even greater importance when ice formation takes place in running and turbulent water, in which case it represents the necessary conditions for the formation of frazil and anchor ice. The supercooling may be observed by a sensitive thermometer when the bulb is heated before being immersed in the water. The degree of supercooling of still water may be more than 1° C. in a thin surface layer as the author has demonstrated by measuring the temperature by a recording thermopile exposed to radiation from the surface. It is emphasized that the state of supercooling in water is a stable one, the formation of ice being dependent upon the existence of nuclei or solid boundary surfaces from which crystallization will start and from which liberated heat of solidification will flow. This process of thermal conduction needs time.
Ice Nuclei in the Ultramicroscope and the Atmosphere
Authors: Fournier d’Albe E. M.
Published: September 2017

Various attempts have been made in recent years to overcome the difficulties inherent in the study of clouds by reproducing them on a small scale in the laboratory. The present article briefly reviews some of these experiments, particularly those relating to the formation of ice crystals, and discusses the extent to which the laboratory results accord with what is known of natural clouds. Recent experiments on the artificial stimulation of rainfall are also examined for the light they throw on the part played by ice nuclei in the formation of rain.
A Contribution to the Study of the Glacier Grain
Authors: Renaud André
Published: September 2017

The melting of glacier ice always begins at the surface of the glacier grains. A mass of glacier ice at a temperature near its melting point is therefore an aggregate of crystals separated by a film of liquid. The electrical conductivity of ice subjected to differential melting differs considerably according to whether the fractions come from the grain surfaces or from the crystal centres, being much the higher in the former case. It is concluded therefore that the glacier grain consists of a crystal of pure ice with a surrounding film of brine, thus verifying the hypotheses of Buchanan and of Quincke on the formation of natural and artificial ice.

The growth of the grain is facilitated by the elimination of the saline skin between neighbouring crystals, the resulting coalescence having the character of autogenous welding. On the other hand, the intergranular film of liquid may act as a lubricant in the as yet inadequately explained mechanism of glacier flow.
Pollen Analysis of Glaciers in Special Relation to the Formation of Various Types of Glacier Bands
Authors: Godwin H.
Published: September 2017

The author describes the work of Dr. V. Vareschi on the pollen content of glacier ice. A general account of the method of analysis is given. The results of statistical evidence of the analyses on several alpine glaciers are discussed, particularly in regard to the general nature of glacier flow in different parts of the glaciers. Vareschi’s suggestions as to the modes of origin of a certain type of ogive banding and of parallel banding (Pflugfurcheneis) are dealt with in the light of his findings. It is pointed out that what appears to be a valuable new approach to the solution of glacier flow problems needs elaboration before it can be accepted in all its bearings.
Dynamics and Structure of Griesgletscher, Switzerland
Authors: Hambrey M. J. , Milnes A. G. , Siegenthaler H.
Published: September 2017

A detailed investigation has been carried out on the dynamics of an Alpine valley glacier of relatively simple shape and the results are considered in relation to the development of secondary structures. Ice velocity reaches a maximum near the top of a small ice fall (40 m a−1) which also coincides approximately with the equilibrium line. Flow lines converge in the accumulation area but are roughly parallel in the ablation area. The “regional” strain-rate pattern is rather complex. Approximate longitudinal extension is evident in the accumulation area and strain-rates reach high values at the south margin and in the ice fall (up to 0.12 a−1). In the ablation area, strain-rates are comparatively small and in general indicate longitudinal compression. “Local” deformation rates obtained in the area beneath the ice fall and along a flow line near one of the margins reveal complex patterns of deformation within small areas.

There is no clear relationship between foliation and strain-rates (and by analogy stresses), except in the case of longitudinal foliation in marginal areas which, if actively developing, lies approximately parallel to a direction of maximum shear strain-rate. It is more important to consider the relationship of this structure to strain history. Results from this study indicate that, regardless of the initial orientation of the foliation in relation to the strain ellipse, it attains approximate parallelism with the long axis of the ellipse as deformation progresses.

It is also shown that many foliations originate from pre-existing layered structures such as stratification or crevasse traces. This problem is discussed particularly with reference to an arcuate foliation which originates in the ice fall and is believed to represent tensional veins, subsequently subjected to compressive strain within and below the ice fall.
An Incremental Formulation of Constitutive Equations for Deposited Snow
Authors: Desrues J. , Darve F. , Flavigny E. , Navarre J.P. , Taillefer A.
Published: September 2017

The behaviour of a snow mass under natural loadings (gravity forces, boundary conditions) can be computed by the finite-element method, in so far as a convenient formulation of the stress–strain relationship for snow is available. This paper deals with such a formulation given in incremental form.

Experiments have been performed, which show that deposited snow can be considered as a non-linear visco-elastic material with memory effect. The proposed theoretical formulation takes into account these properties. The elastic part of the deformation is assumed to be isotropic and non-linear; the viscous part is expressed in terms of a creep-rate, which results from a superposition of elementary creep-rates according to Boltzmann’s principle.

The values of parameters can be obtained from isotropic creep experiments. The experimental data and the resulting parameters are reported.

Since the parameters were determined, the formulation of the rheological law was then tested by integration on “stress–strain paths" corresponding to other experiments of a different type, performed on the same snow. The experiments are triaxial tests at constant axial strain-rate, with a preliminary stage of isotropic compression. Experimental data are compared to theoretical curves obtained by integration of the rheological law. The calculated behaviour is consistent with the experimental results.
A Comparison of Observed and Calculated Avalanche Velocities
Authors: La Chapelle Edward R. , Lang Theodore E.
Published: September 2017

Velocities have been derived from motion-picture film of two different avalanches falling in known terrain. These data are used to calculate avalanche behavior according to the method of Voellmy and the method of Lang and others. Results suggest that Voellmy’s coefficient of turbulent flow may be related to snow density and temperature as much as it is to terrain roughness. For avalanche flow modelled as a transient, viscous process, specification of friction coefficient and kinetic viscosity over a limited range of values successfully predicts a wide range of avalanche behavior.
Recent Developments of Avalanche Forecasting by Discriminant Analysis Techniques: A Methodological Review and Some Applications to the Parsenn Area (Davos, Switzerland)
Authors: Obled Charles , Good Walter
Published: September 2017

Different statistical methods have been tested to answer the challenging problem of forecasting avalanche activity. For each approach, the theoretical background is briefly described, and the main advantages and drawbacks are discussed. The first method consists of a simple discriminant analysis applied to a sample of avalanche days against a sample of non-avalanche days. The second approach tries to take into account different types of avalanche phenomena associated with different types of snow and weather situations. It requires the development of an avalanche typology compatible with the available variables, and leads to a two-stage decision model. A given day is first allocated to a weather type, within which the proper model avalanche-non-avalanche is then processed. A third method, a local non-parametric one, consists of drawing, for the day under study and in an appropriate predictor space, its nearest neighbours from the sample file in order to get an estimate of the probability of avalanche occurrence. For each approach, the explanatory variables may be processed directly as quantitative continuous data or as qualitative categorized data. This removes the problems associated with the very asymmetric distribution of half of them, at the cost of a moderate loss of information. As a rule, the methods were calibrated and then applied to the winters 1972–73 and 1973–74 used as a test sample, thus allowing comparison of their respective potentials in operational forecast.
The Effect of Longitudinal Strain on the Shear Stress of an Ice Sheet: In Defence of Using Stretched Coordinates
Authors: Hutter Kolumban
Published: September 2017

Thickness changes of ice sheets are, except perhaps at the snout region, small as compared to unity. This suggests using a coordinate stretching so as to make the surface changes in the new coordinates of order one. The explicit occurrence of the smallness parameter in the governing equations then allows us to search for perturbation solutions in various problems. Here, it is shown that the classical formula for the basal shear stress follows easily from such a perturbation procedure. Furthermore it can be improved to account for longitudinal strain effects. As compared to previous work in this area, these formulae are explicit and allow us to take vertical variations of material properties into account in a straightforward manner.
Radiation Transmittance through lake ice in the 400–700 nm Range
Authors: Bolsenga S. J.
Published: September 2017

Significant new information on radiation transmittance through ice in the photosynthetically active range (400–700 nm) has been collected at an inland lake near Ann Arbor, Michigan, U.S.A., and at one site on the Great Lakes (lat. 46° 46´ N., long. 84° 57´ W.). Radiation transmittance through clear, refrozen slush, and brash ice varied according to snow cover, ice type, atmospheric conditions, and solar altitude.

Snow cover caused the greatest diminution of radiation. During periods of snow melt, radiation transmittance through snow-covered ice surfaces increased slightly. Moderate diurnal variations of radiation transmittance (about 5%) are attributed to solar altitude changes and associated changes in the direct- diffuse balance of solar radiation combined with the type of ice surface studied. Variations in radiation transmittance of nearly 20% over short periods of time are attributed to abrupt changes from a clear to a cloudy atmosphere.

A two-layer reflectance–transmittance model illustrates the interaction of layers in an ice cover such as snow or frost overlying clear ice. Upper layers of high reflectance have considerable control on the overall transmittance and reflectance of an ice cover.
Numerical Simulation Study of Avalanches
Authors: Brugnot G. , Pochat R.
Published: September 2017

To provide engineers with a better tool, we have developed a program for avalanche computation. After a brief description of the mathematical model and the assumptions, we describe influence of physical and numerical parameters, which allows a better understanding of the physical phenomenon which we call an avalanche. The satisfactory agreement between computations and observations allows us to assume that the model is well founded; further experiments will allow us to improve this simulation tool.
Some Mechanisms of Controlled Moraine Development, Antarctica
Authors: Rains R. B. , Shaw J.
Published: September 2017

Contemporary processes of moraine development at the margins of polar glaciers encompass a wide range of subtly different mechanisms. Two types of “controlled” moraine evolution, applicable to hummocks and transverse moraine ridges, are identified from Wright Lower Glacier and Webb Glacier, southern Victoria Land, Antarctica. Type 1 moraine complexes involve a relatively abundant supply of supraglacial debris, the development of transverse thrust blocks in the ablation-zone ice and the subsequent re-arrangement of ablation debris in ablation cusps and on inactive thrust blocks. Relict landform suites, apparently formed in this manner, reveal large coarse-grained hummocks inset behind moraine ridge remnants.

Type 2 moraines may develop where the supply of supraglacial debris is meagre but the growth of ablation cusps concentrates primarily englacial debris into small irregular hummocks. The gravel component of this debris is usually of finer texture than for type 1 deposits, reflecting abrasion/attrition effects of prior englacial transportation. Transverse moraine ridges may or may not be associated with type 2 hummocks, depending on local variations of ice motion, ice decay, and debris supply.
An Inexpensive Remote Snow-Depth Gauge based on Ultrasonic Wave Reflection from the Snow Surface
Authors: Gubler H.
Published: September 2017

Total snow depth is determined by measuring the time of flight of an ultrasonic wave packet emitted from a sonic transmitter above the snow surface and reflected from the snow surface back to the receiver/transmitter system. The light-weight system is battery powered (operating time without battery change at least 8 months) and can be fixed to any post above the snow surface. The absolute precision is better than ±0.03 m. Data and commands are transmitted by a single two-wire system up to several kilometres.
An Electronic Remote Snow-Drift Gauge
Authors: Gubler H.
Published: September 2017

Snow transportation by wind in potential avalanche fracture zones is a very important parameter for avalanche forecasts. A special battery-powered photoelectric sensor has been developed by the Eidg. Institut für Schnee- und Lawinenforschung, Weissfluhjoch/Davos. The output pulse rate is proportional to the mass flux (units of kg m–2 s–1). Drift particles larger than 50 μm in diameter are classified according to their volumes in five classes. The accuracy of the flux measurement is ±50% and is limited by physical factors and not by the apparatus.
Flutes on Bare Bedrock
Authors: Karlén Wibjörn
Published: September 2017

Flutes, up to about 500 m long, were observed on bare glacially polished bedrock at the margin of the glacier Svartisen in northern Norway. Since these ridges were lying directly on bedrock that had no till cover, they can hardly have been formed by post-depositional deformation of pre-existing materials, a mechanism for formation favoured by Boulton.
Systems for Measuring Thickness of Temperate and Polar Ice from the Ground or from the Air
Authors: Watts Raymond D. , Wright David L.
Published: September 2017

Equipment has been designed and tested for ground-based and airborne sounding of temperate glaciers. The transmitter is a free-running pulse generator that uses avalanche-mode transistor breakdown to create high-voltage pulses. The transmit and receive antennas are resistively loaded dipoles; for the airborne system, a twin-lead transmit element and a three-layer coaxial receive element are used on the inboard end of the respective antennas. The sounders are broadband systems; oscilloscopes are used for receivers. The oscilloscope trace is recorded photographically in the ground-based systems. A sampling oscilloscope is used in the airborne system—the sampling process strobes the waveform to audio frequencies so that it can be recorded on magnetic tape. Echoes have been obtained from ice depths of 550 m using the airborne system and about 1 000 m using the ground-based system.
A Visible and Near-Infrared Scanning Photometer for Field Measurements of Spectral Albedo and Irradiance under Polar Conditions
Authors: Grenfell T. C.
Published: September 2017

The design and operating characteristics are presented for a visible and near-infrared scanning photometer which can measure incident and reflected spectral irradiance from 400 nm to 2 450 nm. The instrument is designed to record over 98% of the solar radiation incident upon and reflected from the Earth’s surface using a turret-type cosine collector and a circular variable interference filter. The apparatus has been tested successfully on Arctic sea ice at temperatures down to –20°C. It is self-contained and easily portable, and its mass is less than 16 kg. Some preliminary results are presented.
Evidence for a Former Large Ice Sheet in the Orville Coast–Ronne Ice Shelf Area, Antarctica
Authors: Carrara Paul
Published: September 2017

The Orville Coast area of the Antarctic Peninsula was extensively glacierized in the past. Striations, polished rock surfaces, and erratics on nunatak summits indicate that this area was covered by a broad regional ice sheet whose grounded ice margin was on the continental shelf, in the present-day Ronne Ice Shelf area. If the glacial history of Antarctica has been controlled by eustatic sea-level changes, the destruction of this ice sheet would have been contemporaneous with that of the Ross Sea ice sheet due to the world-wide rise of eustatic sea-level at the end of the Wisconsin glaciation.