bluuebunny/crossref_metadata_2025 huggingface dataset:
Snow-creep forces on masts
Authors: Larsen Jan Otto
Published: September 2017

Since 1975, the Norwegian Geotechnical Institute has performed field investigations of snow-creep forces on masts at the research site in Grasdalen, Stryn mountains in Norway. Two poles, with diameters of 419 and 219 mm, respectively, were erected at the site together with a retaining structure. On both poles, strain gauges were mounted in pairs every 0.5 m to find the axial stresses and the moments in different sections. In the middle section of the retaining structure, the beams and supporters were instrumented to obtain measurements of the strains and stresses. Snow glide was controlled by glide shoes mounted at the rock surface above the structures.

During the winter, snow profiles were made systematically; these included measurements of snow depth, density and temperature, and observations of snow type and moisture content. By relating the measured stresses and moments in the structures to the snow depth, it was possible to find the snow-pressure distribution. A comparison of the snow pressures with the “Body force index” (product of snow depth h, density ρ and acceleration due to gravity g), show a close relationship for the wall element. For the pole elements, the snow temperature during the winter is an added factor of high importance and the highest pressures on these elements occur in winters with long periods of 0°C isothermal snowpack.
Daytime preservation of surface-hoar crystals
Authors: Hachikubo Akihiro , Akitaya Eizi
Published: September 2017

Surface hoar growing for several clear and humid days were observed. During daytime, air and snow-surface temperature increased and relative humidity decreased, hence evaporation (sublimation) occurred at the snow surface. The amount of evaporation calculated using a bulk-transfer method suggests that the surface-hoar crystals which grew during the previous night should have disappeared but they were observed to survive on the snow surface even during the daytime. During the following night, new surface-hoar crystals formed on top of the older ones and grew even larger. This result indicates that, although the surface-hoar crystals evaporated into the air during the daytime, snow grains beneath the surface were warmed by solar radiation and evaporated to the air. They may partially condense into the surface-hoar crystals and make up for the reduction in size. Depth-hoar crystals formed beneath the snow surface for several days and the surface layer, composed of both types of hoar crystal, showed a very weak shear strength.
Statistical prediction of maximum avalanche run-out distances from topographic data in the western Catalan Pyrenees (northeast Spain)
Authors: Furdada Glòria , Vilaplana Joan Manuel
Published: September 2017

We present regression models to estimate maximum avalanche run-out distances in the western Catalan Pyrenees (northeast Spain). The regression equations have been calculated from topographic parameters of 216 well-known avalanche paths, mapped on avalanche location maps at a scale of 1: 50 000. Historical information about avalanche maximum run-out zones has been available for some avalanche paths hut most of them have been delimited by vegetation and geomorphological indices.

The avalanche profiles, which are representative of avalanche paths, have been classified on the basis of avalanche run-out zone morphology, because this has a considerable influence on avalanche behaviour and run-out. Three classes have been defined and regression equations obtained for each class and also for the total. Finally, some examples have been calculated in order to appreciate the applicability of the models to improving avalanche mapping.
Physical and numerical analysis of the front of a gravity current on a horizontal bottom
Authors: Naaim Mohamed , Pellarin Thierry
Published: September 2017

In this paper, numerical and experimental approaches are applied to analyse the dynamics of the front of a gravity current. This study focused on two parameters: internal density and velocity fields. The salt concentration was determined by a potentiometric process. The internal velocities were determined using an optical device and an image-processing system. The structure of the head of the gravity current was analysed. Its density was measured and two stages of evolution were observed. This analysis allows us to coufirm the existence of two important stages. For xf < xs, where the dynamics depend on the initial condition, the flow consists of a head and body and the front density is constant. For xf > xs, we show that the density of the front decreases and evolves towards the Hallworth and others (1993) law. From a comparison between the experiments and the numerical model, we show that the numerical model, which is based on Navier–Stokes equations and on the k−L turbulence model (where L is the height of the gravity current), can predict well flow in the slump regime and in the inertia–buoyancy regime with smoothed results in the transition from the head to the body of the gravity current.
Probabilistic evaluation of snow-slab stability on mountain slopes
Authors: Chernouss P. A. , Fedorenko Yu.V.
Published: September 2017

The results from a numerical- probabilistic experiment aimed at evaluating avalanche-release probabilities are presented in order to show the problems and the possibilities of such an approach. A snow slab on a mountain slope is modeled as a thin elastic non-moment shell resting on a three-dimensional hard underlying surface. The thickness of snow is considered as an inhomogeneous Gaussian spatial random field with a predetermined covariance that was obtained previously by field measurements. The stress distribution σ(x, y) is calculated by solving the equations of equilibrium using a finite-difference method with a mesh of lines of curvature on a mountain slope. As a criterion of avalanche release, exceeding some threshold value of stress σthres; by the calculated value σ(x, y) is applied. The field P(σ(x, y) > σthres; x, y) derived, using the Monte-Carlo method, is regarded as a measure of the spatial distribution of avalanche-release probability. This simulation scheme at present has no claim to forecast avalanche release but may be used to pinpoint the importance of snow distribution on a slope.
Study of avalanche dynamics by seismic methods, image-processing techniques and numerical models
Authors: Sabot F. , Naaim M. , Granada F. , Suriñach E. , Planet P. , Furdada G.
Published: September 2017

Seismic signals of avalanches, related video images and numerical models were compared to improve the characterization of avalanche phenomena. Seismic data and video images from two artificially released avalanches were analysed to obtain more information about the origin of the signals. Image processing was used to compare the evolution of one avalanche front and the corresponding seismic signals. A numerical model was also used to simulate an avalanche flow in order to obtain mean- and maximum-velocity profiles. Prior to this, the simulated avalanche was verified using video images. The results indicate that the seismic signals recorded correspond to changes in avalanche type and path slope, interaction with obstacles and to phenomena associated with the stopping stage of the avalanche, suggesting that only part of the avalanche was recorded. These results account for the seismic signals previously obtained automatically in a wide avalanche area.
Slushflow hazard — where, why and when? 25 years of experience with slushflow consulting and research
Authors: Hestnes Erik
Published: September 2017

Slushflows — flowing mixtures of water and snow — are a major natural hazard in Norway. Knowledge gathered by the Norwegian Geotechnical Institute during 25 years of slushflow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushflow release, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushflow release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute-hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushflows occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity.
Atmospheric and hydrological boundary conditions for slushflow initiation due to snowmelt
Authors: Scherer Dieter , Gude Martin , Gempeler Markus , Parlow Eberhard
Published: September 2017

Slush-flows of a large variety of magnitudes were observed during three field campaigns to Liefdefjorden, northwestern Spitsbergen, and one campaign to Kärke-vagge, northern Sweden. In the latter campaign, the release and movement of a slush torrent was documented on video and in photographs. Meteorological and snow-hydrological measurements carried out during these campaigns were analysed with respect to slushflow initiation due to snow-melt.

Since slushflows are quite common in polar and sub-polar drainage basins (although they are not restricted to these regions), specific atmospheric and hydrological boundary condittons must be fulfilled for slushflow initiation due to snowmelt. Radiative fluxes, air temperatures and wind velocities are the most important atmospheric variables, while snow depth, depth of the water-saturated layer, hydraulic conductivity and snow structure are the primary snow variables of interest.

It has been shown that slushflows can be released due to energy input in the snow cover by net radiation and sensible heat within the ordinary range of the high-latitudinal snow melt period. Slush torrent initiation is intensified by a superpositton of both energy fluxes. Infiltration losses were not significant even when permafrost was not present. Crucial for slushflow initiation due to snowmelt is the timing of energy input and meltwater flow through the snowpack.
Snowmelt and slushflows: hydrological and hazard implications
Authors: Gude Martin , Scherer Dieter
Published: September 2017

In many high-latitude areas, slushflows occur frequently during the snowmelt period but information on the initiation mechanism is rare. Field observations and measurements of slushflows in northwestern Spitsbergen and in northern Sweden demonstrate the role of meltwater accumulation and the hydraulic pressure gradient in the release process. Snow metamorphism is revealed to be of minor importance in the observed events. The monitoring of water-pressure development in a saturated snow cover demonstrates that preferred release areas are within low-gradient valley sections, where meltwater inflow is higher than outflow.

Slushflows consist of mudflow-like flowage of water-saturated snow along stream courses. They represent transitional processes between fluvial floods and avalanches. On the other hand, they possess unique characteristics concerning release and movement. The comparative evaluation of definition items for fluvial floods, slushflows and avalanches offers hasic data suitable for a risk assessment.
Irreducible water saturation in snow: experimental results in a cold laboratory
Authors: Coléou Cécile , Lesaffre Bernard
Published: September 2017

The porosity of wet snow is often about 50%; however, liquid water generally fills less than 10% of this pore volume. In order to relate the irreducible water content trapped in snow to its characteristics, we have conducted experiments in a cold laboratory. The results show that irreducible water content, expressed as per cent of mass, depends only on porosity. Experimental studies were restricted to homogeneous wet snow samples. Therefore, we can only achieve a valid result in natural snowpacks when applying to an homogeneous layer of wet snow. Nevertheless, the results may be incorporated into snow-cover energy-balance models to improve the retention and percolation predictions. The thickness of the water-saturated layer observed at the base of the sample in our experiments, was related to the ratio of the mean convex radius of curvature to dry density.
Measurement of density and wetness in snow using time-domain reflectometry
Authors: Schneebeli Martin , Coléou Cécile , Touvier François , Lesaffre Bernard
Published: September 2017

Time-domain reflectometry (TDR) is widely used in soil physics to determine water content. Existing equipment and methods ran be adapted to measurements of snow wetness. The main advantages compared to other methods are flexibility in constructing sensors, minimal influence on snow cover during measurements and sensors can be multiplexed. We developed sensors suitable for continuous and non-continuous measurements of snow wetness and density, measured the apparent permittivity in different snow densities and snow types, and compared the measurements to existing mixing formulas for mixtures of snow and air. In dry snow, density was measured from 110 to 470 kg m−3. The residual error is 14 kg m −3 and the 95% confidence interval of our model is 3 kg m−3. To measure snow density and wetness continuously suitable sensors have been constructed. Their small size and high surface area to weight ratio minimizes their movement in the snowpack, except when they are exposed to intense solar radiation. Results show that changes in dry-snow density of less than 5 kgm−3 can be detected. Infiltration of even small amounts of water clearly shows up in the permittivity. At the surface of the snowpack, problems occur due to the formation of air pockets around the sensors during long-term measurements.
Acoustic impedance measurement of snow density
Authors: Marco O. , Buser O. , Villemain P. , Touvier F. , Revol Ph.
Published: September 2017

Today, it is possible to estimate the density of snow in many different ways (gravimetry, attenuation of gamma rays and velocity of electromagnetic waves). In this paper, we suggest using the acoustic properties of snow. First, we recall the main studies on the acoustic properties of snow. Then, we show, from laboratory measurements, the correlation between density and the acoustic parameters of snow. We found a very good correlation between density and the modulus of the normalized characteristic impedance. We also show that use ofa three-parameter model simulating the propagation of an acoustic wave in porous media allows one to calculate the density of snow from its acoustic porosity.
Accumulation-rate variations around Summit, Greenland
Authors: Bolzan John F. , Strobel Michael
Published: September 2017

Shallow cores to about 17 m depth were recovered at nine sites distributed on a 150 km × 150 km survey grid centered Summit in central Greenland. Measurements of the stable oxygen-isotope ratio and the gross β activity as a function of depth enable annual summer horizons to be identified and dated. From these data, average accumulation rates were computed with an uncertainty of about 5–8%. The contours of constant accumulation rate in the region suggest a primary moisture flux from the southwest of the grid. Similarly, contours of the average oxygen-isotope ratio are consistent with the progressive isotopic depletion of a precipitating air mass moving from the southwest, and automatic weather-station data indicate that the moisture flux tends to be largest from the southwest quadrant. The annual variation in the total accumulation over the grid shows no persistent trend over the interval 1964–87 common to all cores.
Distribution of stable isotopes in surface snow along the route of the 1990 International Trans-Antarctica Expedition
Authors: Dahe Qin , Petit J.R. , Jouzel J. , Stievenard M.
Published: September 2017

This paper presents the distribution of average δD andδ18O values for the top 1 m of surface snow for a large area of Antarctica. The samples were collected on the 1990 International Trans-Antarctica Expedition which crossed the continent from the northern tip of the Antarctic Peninsula to Mirny Station. The empirical relationships between the isotopes, temperature and elevation are computed. The slopes of δD with respect to the surface temperature for the segments west (Patriot Hills-Vostok) and east of Vostok (Komsomolskaya-Mirny) are not significantly different to that observed between Dumont d’Urville and Dome C (Lorius and Merlivat, 1977) which are often used to interpret deep ice-core isotopic profiles. There is, however, a noticeable shift between the two regression lines with, for a given temperature, higher isotopic values west of Vostok. The deuterium excess values increase sharply at 3000 m.a.s.l. on the plateau, confirming the results of Petit and others (1991).
Internal melt figures in ice by rapid adiabatic compression
Authors: Gagnon R.E. , Tulk C. , Kiefte H.
Published: September 2017

Single crystals and bicrystals of water ice have been adiabatically pressurized to produce, and clearly illustrate, two types of internal melt figures: (1) dendritic figures that grow from nucleation imperfections on the specimen’s surface, or from air bubbles at grain boundaries, into the ice as pressure is elevated; and (2) compression melt fractures, flat liquid-filled disks, that nucleate at imperfections in the crystal and grow with the application of pressure eventually to sprout dendritic fingers at the periphery. The transparency of the ice permitted visualization of the growth and behavior of the figures, and this could be an important tool in understanding the role of phase transformations in deep-focus earthquakes. Correlation between figure size and pressure is noted for the first time.
A Finite-element Model of Antarctica: sensitivity test for meteorological mass-balance relationship
Authors: Fastook James L. , Mike Prentice
Published: September 2017

A finite-element solution of the time-dependent mass-continuity equation for column-averaged ice-sheet flow and sliding is applied to the Antarctic ice sheet. First, a calibration of the model to the steady-state present ice-sheet configuration is presented. With fitted values of the parameters describing the regions of sliding, the degree of bed coupling and the ice hardness, a change in the mean annual sea-level temperature is used to simulate variation of the climatic conditions over Antarctica for both warming and cooling of the climate. Paradoxically, a climate warming of up to 9 deg leads to an increase in ice volume, while cooling leads to decreasing ice volume as long as the present margins of Antarctica are maintained. Some extreme simulations of the Antarctic ice sheet for “maximum over-riding” and “minimum warm climate” are shown for situations where the present bed conditions are altered. Finally, a time-dependent simulation shows the response of the ice-sheet system to cyclical variations in the simulated climate, demonstrating the lag of the ice-sheet response to be approximately 2700 years.
Unusual flood events from an Alpine glacier: observations and deductions on generating mechanisms
Authors: Warburton J. , Fenn C R.
Published: September 2017

Observations are presented on a particularly unusual sequence of flood events witnessed at Bas Glacier d’Arolla, Switzerland, in July 1987. The sequence was triggered by heavy rain storms, and involved a supraglacial “overflow event” (water cascading from moulins over the snout of the glacier) succeeded, following a series of “mini-floods”, by a subglacial “outburst event”. Available hydrological and geomorphological data are used to assess the significance of the floods and to deduce likely explanations for each phase of the flood-event sequence. Bottom-up surcharging of a poorly developed subglacial drainage system is the preferred explanation for the overflow event. The subglacial outburst is explained as an extreme “spring event”. Hydraulic jacking is implicated, but not proven, during both events. Whilst the flood sequence was triggered by an intense storm, englacially stored waters are believed to have contributed most of the flood waters.
Observations of a rift in the Ronne Ice Shelf, Antarctica
Authors: King E.C.
Published: September 2017

During seismic profiling on the northwest Ronne Ice Shelf Antarctica, a rift in the ice shelf was encountered. The rift trends southeast to northwest and is located approximately 30 km inland from the present-day ice front The rift is 340 m wide and the surface elevation of the ice shelf drops by 14.65 m over the axis of the rift. The rift has an asymmetrical base with a near-vertical ice-water interface on its northeast flank and a more gently dipping ice-water interface forming its southeastern flank. The ice shelf thins from a thickness of 350 m away from the rift to a thickness of 225 m at the rift axis. The rift is the probable location of a future major calving event on this section of the Ronne Ice Shelf, an event which would release an iceberg of up to 30 km by 180 km into the Weddell Sea.
On the Formulation of Basal Debris Drag for the Case of Sparse Debris
Authors: Snoemaker E.M.
Published: September 2017

Two models are presented for the formulation of abrasion and basal drag due to rock–rock friction (debris drag) for the case of sparse debris entrained in the basal layers of a temperate glacier resting on a bedrock bed. The first model is formulated in terms of average basal melting rate, va, and the concentration, C, of basal debris fragments which make intermittent bed contact. The second model is formulated in terms of vn the component of ice velocity normal to the bed flowing around rock fragments contacting the bed, and Cc, the concentration of debris actually in contact with the bed. The relationship between the two models is given for the case of a sinusoidal bed. Generalizations are discussed as well as potentially important physical processes which remain to be investigated.
Composition, Internal Structures, and an Hypothesis of Formation for Drumlins, Waukesha County, Wisconsin, U.S.A.
Authors: Richard Whittecar G. , Mickelson David M.
Published: September 2017

Late Wisconsin-age drumlins west of Milwaukee are clustered atop uplands bounded by discrete scarps. Gravel operations within the uplands have exposed drumlin cores of undeformed till and outwash beds which are truncated at the sides of the drumlin. In a few areas, clastic dikes, faults, overturned bedding and shear folds disturb the original layering. The drumlin shapes are blanketed with a basal till 1–3 m thick (“retreat” till) which truncates all internal structures. This till covering cannot be distinguished from the youngest truncated till (“advance” till).

Truncation of all of these structures shows that these drumlins are erosional forms carved from pre-existing drift. Apparently, during erosion under compressive flow, some beds became unstable and initiated large-scale movements of material into the drumlin from beneath the drumlin form. Failure and mobilization of the finer-grained beds may have been due to increased pore pressures, differing stages of dilatancy, or differing bulk densities. A growth relationship for drumlins may exist that is based upon the rates of material moving into the drumlin from below and rates of erosion of the drumlin form.
Mercury-in-Glass Thermometers for Precise Temperature Measurements Near 0°C
Authors: Osterkamp T. E.
Published: September 2017

Experience with the calibration and field use of mercury-in-glass calorimeter thermometers provides an indication of the accuracy attainable and the necessary corrections to obtain that accuracy. Secular changes as large as 57 mK have been observed during the first three years of thermometer use. Light physical tapping is found to reduce the thermometer readings by 3–6 mK. Corrections for variations in the external and internal bulb pressure and care to avoid parallax are necessary to obtain the best accuracy in field measurements. The best accuracy obtainable with these thermometers for temperature measurements near 0°C is approximately ±4 mK for laboratory measurements and ±5 mK for field measurements.
Structural characteristics of congelation and platelet ice and their role in the development of antarctic land-fast sea ice
Authors: Jeffries M. O. , Weeks W. F. , Shaw R. , Morris K.
Published: September 2017

Ice cores were obtained in January 1990 from the land-fast ice in McMurdo Sound for a study of variations in texture, fabric, sub-structure, composition and development. Two primary ice types were observed, congelation and platelet, with a minor amount of frazil ice. Congelation ice growth precedes platelet-ice accretion. Congelation-ice fabrics show frequent moderate to strong alignments, a phenomenon believed to be due to water-current control of selective ice-crystal growth. Platelet ice originates at the base of the congelation ice, initially as a porous latticework of tabular ice crystals which subsequently consolidate by congelation of the interstitial water. Interstitial congelation-ice fabrics generally have little or no alignment, indicating the reduced effect of currents within the platelet latticework prior to solidification. Platelet-crystal textures range from small, wavy-edged forms to large, blade-like forms. Platelet-crystal fabrics indicate that, in addition to being randomly oriented, the platelet latticeworks commonly include many crystals with their flat (0001) faces oriented both parallel and normal to the base of the overlying ice. Plate-width data suggest that the interstitial congelation ice-growth rates remain similar to those of the overlying congelation ice. This effective increase in growth rates probably happens because the latticework of accumulating platelets ahead of the freezing interface ensures that the water within the platelet layer is at the freezing point and less heat has to be removed from platelet-rich water than from platelet-free water for a given thickness of congelation ice to grow. The negative oceanic heat flux associated with platelet-ice formation in McMurdo Sound explains why McMurdo Sound fast ice is thicker than Ross Sea pack ice, and also why it reaches a greater thickness than Arctic fast ice grown in a similar polar marine climate. Plate widths in the McMurdo Sound congelation ice suggest, however, that it grows no faster than Arctic congelation ice.
Airborne particles in snow
Authors: Heintzenberg Jost , Rummukainen Markku
Published: September 2017

In a pilot experiment, airborne particles were shown to exist in snow. In newly deposited snow they could be traced down to 17 cm below the surface. With our particle sensor, the snow was ventilated on the level of expected natural ventilation velocities. We show with a simple deposition model that air/snow exchange of airborne particles must be considered in the interpretation of impurities in snow and glacier ice. However, the relative magnitude of ventilation velocity compared to dry-deposition velocities at the surface is of crucial importance for determining total deposition. In particular, in ice sheets with high ventilation velocities, seasonal variations in atmospheric concentrations can be dampened and age distributions of deposited particles need to be considered similarly to the occlusion of gases.
High-resolution dielectric profiling of ice cores
Authors: Moore J. C.
Published: September 2017

A new method for high-resolution (3 mm) dielectric profiling of ice cores is described. The method measures the capacitance and conductance of the ice at a single frequency (chosen to be 50 kHz in this case). The technique requires only a few minutes per metre of core, and no sophisticated data analysis. The system is designed to operate on ice cores that have been cut longitudinally, providing one flat and one curved surface. The 50 kHz conductance is dependent on the acid and neutral-salt concentrations in the ice. The new method was tested successfully on the GRIP core from Summit, Greenland, in 1991. It is useful for detecting seasonal variations in impurities in both acidic Holocene ice and in normally alkaline Wisconsin ice.
Is there direct evidence for late Quaternary collapse of the West Antarctic ice sheet?
Authors: Burckle Lloyd H.
Published: September 2017

By studying diatoms recovered from sediment taken from beneath the West Antarctic ice sheet (Ice Stream B), Scherer (1991) concluded that this feature must have collapsed at least once during the past 600 kyear and that the two likely candidates for time of collapse were oxygen-isotope stage 11 (362–423 kyear BP) and sub-stage 5e (110–128kyear BP). This conclusion does not stand up to critical examination of the data, however. Specifically, the diatom datum level, the last occurrence of Actinocyclus ingens, used to constrain the 600 kyear date is diachronous into higher latitudes and does not apply in sediments recovered from near Antarctica. Secondly, the additional diatoms used to constrain the time of collapse to the late Quaternary either range before the late Quaternary or have no published geological record. In spite of this, there are data to suggest that one or more late Quaternary interglacial intervals were as warm as, or warmer than, the present. As yet, however, no direct evidence exists to incorporate a West Antarctic ice sheet collapse into these scenarios. It is suggested that this debate is best resolved by study of deep-sea sediments of late Quaternary age recovered from around the Antarctic continent.
Ice-flow features on Ice Stream B, Antarctica, revealed by SPOT HRV imagery
Authors: Merry Carolyn J. , Whillans Ian M.
Published: September 2017

Numerous features of glaciological significance appear on two adjoining SPOT High Resolution Visible (HRV) images that cover the onset region of Ice Stream B, Antarctica. Many small-scale features, such as crevasses and drift plumes, have been observed in aerial photography. Subtle large-scale features, such as long flow traces that have not been mapped previously, are clear in the satellite imagery. Newly discovered features include ladder-like runners and rungs within certain shear margins, flow traces that are parallel to ice flow, unusual crevasse patterns and flow traces originating within shear margins.
Interpretation of radar-detected internal layer folding in West Antarctic ice streams
Authors: Robert W. Jacobel , Anthony M. Gades , David L. Gottschling , Steven M. Hodge , David L. Wright
Published: September 2017

Low-frequency surface-based radar-profiling experiments on Ice Streams Β and C, West Antarctica, have yielded high-resolution images which depict folding of the internal layers that can aid in the interpretation of ice-stream dynamics. Unlike folding seen in most earlier radar studies of ice sheets, the present structures have no relationship to bedrock topography and show tilting of their axial fold planes in the flow direction. Rather than being standing waves created by topography or local variations in basal shear stress, the data show that these folds originate upstream of the region of streaming flow and are advected into the ice streams. The mechanism for producing folds is hypothesized to be changes in the basal boundary conditions as the ice makes the transition from inland ice to ice-stream flow. Migration of this transition zone headward can then cause folds in the internal layering to be propagated down the ice streams.
The tensile strength of first-year sea ice
Authors: Menge J. A. Richter , Jones K. F.
Published: September 2017

We present the results of tests done to determine the tensile behavior of first-year columnar sea ice over a range of temperatures from −20° to −3°C and strain rates of 10−5 and 10−3s−1. The temperature of a test specimen was dictated by its in-situ location within the sea-ice sheet; samples located near the top of the sea-ice sheet were tested at the lower temperatures. A tensile load was applied along the cylindrical axes of the test specimens, which were perpendicular to the growth direction of the ice. Results showed that the maximum stress reached during a test was most strongly influenced by temperature, while the failure strain and the modulus were principally affected by the loading rate. A model relating the tensile strength of the ice to its porosity based on temperature-dependent variations in the brine-pocket geometry is evaluated.
End-capping procedure for cored ice samples used in tension tests
Authors: Richter-Menge J. A. , Claffey K.J. , Walsh M. R.
Published: September 2017

This note describes an end-capping procedure used to prepare cylindrical ice-core samples for direct tension testing. The techniques developed build on work done by Cole and others (1985) and Lee (1986), and include a design modification to the loading train and a more reliable approach to establishing the fresh-water bond used to mount the end caps on the sample. Using these techniques, an 88% success rate was achieved in a recent series of uniaxial tension tests.
The Modeling and Measurement of the Deformation of a Sloping Snow-Pack
Authors: Lang Theodore E. , Sommerfeld Richard A.
Published: September 2017

The modeling of deformation in snow-pack of realistic geometry is reported. Experimentally measured deformation rates are compared with corresponding rates predicted from a finite-element model developed using local stratigraphy in the experimental area. Specifically designed deformation gages placed on an avalanche-sensitive snow slope at Berthoud Pass, Colorado, during the winter of 1972-73, were used to measure the experimental values. The finite-element code, based upon a plane-strain idealization, was used to model the steady-state flow of the slope. The program incorporates visco-elastic properties of the snow-pack, snow-layer stratigraphy, and the orthotropic properties of snow when both tension and compression components of stress act at a point. The degree of correlation between experimental and computed values of deformation rates is reported, and limitations of the analysis in conjunction with the type of experimental data taken are discussed.
Indentation Tests to Investigate Ice Pressures on Vertical Piers
Authors: Croasdale K. R. , Morgenstern N. R. , Nuttall J. B.
Published: September 2017

Controlled field and laboratory tests were performed to investigate the relationship between ice strength and the maximum ice pressures on vertical piers. The apparatus used in the field tests consisted of a flat indentor (75 cm wide) which was pushed through the ice by hydraulic rams. 27 tests were conducted on lake ice up to one metre thick. Ice pressures in the range 2.5 to 5.0 MPa were obtained for ice in good initial contact with the indentor. The ice pressures exhibited little sensitivity to variations in temperature, ice thickness and strain-rate for the range 7.5 × 10-7 to 4.4 × 10-3 s-1.

The average unconfined compressive strengths obtained in the laboratory were about 20% higher than the average field ice pressures. In addition, the laboratory strengths were found to be sensitive to temperature, and to strain-rate in the range 1 × 10-7 to 1 × 10-3 s-1. The confined compressive strength was two to three times the unconfined strength.

The failure modes observed in the indentation tests were similar to those predicted (before the tests) by an upper-bound plasticity model. The ability of the model to relate small-scale ice strength to field ice pressures is discussed.
Spontaneous Fracture Initiation in Mountain Snow-Packs
Authors: Lawrence William St. , Bradley Charles
Published: September 2017

Over the past few years an investigation has been conducted to determine the extent of seismic signals associated with avalanching snow slopes. A number of the signals recorded have been examined and classified according to their origin. One of these signals, however, is not clearly defined in terms of an observable source mechanism. To obtain information regarding the origin of this signal we have compared the results from several investigations conducted to study the seismic activity associated with glaciers. A comparative analysis of the snow and glacier signals indicates that the high-frequency signals observed in snow fields are due to internal fracture within the snow.
Mathematical Simulation of the Process of Motion of a Snow Avalanche
Authors: Grigoryan S. S. , Ostroumov A. V.
Published: September 2017

A “hydraulic" model of the motion of bed-type snow avalanches is developed, its qualitative particularities are discussed, and results of comparison of prediction and observations are presented. The proposed model allows calculation of the parameters of motion of snow avalanches possible for a given bed depending on the snow situation and other conditions. The characteristics concerned are the distribution of velocities averaged over the cross-section of the flow and the thickness of snow in an avalanche at every instant of its motion.

The class of avalanches considered is that in which a compact snow flow moves along a distinct avalanche bed consisting of an accumulation region, a bed, and an avalanche cone. It is proposed to model the avalanche bed with a certain inclined and curved channel of given width and shape of cross-section. The characteristics of the model channel are defined on the basis of a topographic map of the corresponding avalanche bed. The motion of avalanche snow is modelled by the flow of an incompressible “liquid" subjected to the action of gravity, internal resistance, and external friction. Destruction and capture of undisturbed snow by an avalanche from the slope is accounted for by introducing into the equations of motion distributed sources of mass the intensity of which depends on the sought characteristics of the problem and which is defined while solving the problem.

On the basis of simple physical considerations connected with the finite shear stress in the snow, it is shown that for sufficiently large avalanches the specific friction force becomes inversely proportional to the thickness of the flow. The proposed mechanism of friction explains the abnormally high mobility of catastrophically large avalanches.

The adopted model possesses a number of properties agreeing qualitatively with the observational data for avalanches. Computer solutions have the form of rather prolonged flows with the shape of the front part typical for avalanches and with characteristic wave formations in the flow which sometimes result in pulsating regimes of motion. The report concludes with results of comparison of predicted and observed characteristics of motions of avalanches for some real avalanche beds demonstrating possibilities of the proposed model.
A Numerical Ice-Accretion Model
Authors: Ackley S. F.
Published: September 2017

A numerical model is developed for calculating the rate and total amount of ice accretion under atmospheric conditions. The principal application of the numerical approach is to aircraft icing and more specifically, helicopter icing problems. These problems are best solved using numerical techniques because of three factors: (1) the dependence of the ice accretion rate on the amount of ice previously deposited, (2) the existence of two different ice growth regimes, the “dry" and “wet" growth regimes, determined by the surface temperature of the accreting surface, and (3) variable velocities (e.g. along rotor blades) which affect the rate of capture of swept-out water droplets and the amount of heat generated by the flow on the accreting surface. These three factors cause feedback in the two governing equations for determining the mass rate of ice accumulation.

The first of these equations is for the mass rate of water captured, and the second equation is for the heat balance of the accreting interface. For the numerical calculation, the object, such as a helicopter rotor blade, is broken down into elements of constant velocity, and for each time step the resulting ice thickness is used to recompute new cross-sectional and surface areas which are then used as input to the next time step. Changes in the cross-sectional and surface areas caused by ice build-up affect both the mass rate (directly through the cross-section and indirectly through a change in collection efficiency) and the heat balance (directly through the cross-sectional and surface areas and indirectly through changes in the collection efficiency and Reynolds number). An additional instability in the ice growth rate develops when the transition between wet and dry growth occurs, enhancing the feed-back that already exists between the mass rate of ice accumulation and the thickness previously deposited. Numerical icing simulations using various helicopter configurations and the icing conditions they typically encounter are presented.
A Method to Estimate Open Pack-Ice Thickness from Two-Day Sequences of Side-Lapping Satellite Images
Authors: Feldman Uri
Published: September 2017

A method to estimate open pack ice thickness drifting in a marginal ice zone (MIZ) is presented, The estimates are obtained from two-day sequences of sidelapping Landsat-1 MSS images and two-day sequences of wind field data by four steps: estimating the surface wind speed, estimating the angle of sea ice deflection, estimating three ratios between ice parameters and estimating the lower and upper limits of pack ice thickness. The method has been applied to six groups of open pack ice floes drifting in the MIZ of the Beaufort Sea during 1973–1975. In the absence of simultaneous in-situ observation, the results have not been tested, The method presented may be applied to any MIZ. Rather than using Landsat-1 MSS images, data from a high resolution active microwave remote sensing system should be employed in the future as its data will be independent of sun illumination and cloud cover.
Snow Mapping and Classification from Landsat Thematic Mapper Data
Authors: Dozier Jeff , Marks Danny
Published: September 2017

Use of satellite multi-spectral remote-sensing data to map snow and estimate snow characteristics over remote and inaccessible areas requires that we distinguish snow from other surface cover and from clouds, and compensate for the effects of the atmosphere and rugged terrain. Because our space-borne radiometers typically measure reflectance in a few wavelength bands, for climate modeling we must use inferences of snow grain-size and contaminant amount to estimate snow albedo throughout the solar spectrum. Although digital elevation data may be used to simulate typical conditions for a satellite image, precise registration of an elevation data set with satellite data is usually impossible. Instead, an atmospheric model simulates combinations of Thematic Mapper (TM) band radiances for snow of various grain-sizes and contaminant amounts. These can be recognized in TM images and snow can automatically be distinguished from other surfaces and classified into clean new snow, older metamorphosed snow, or snow mixed with vegetation.
Airborne Radio Echo-Sounding in Shirase Glacier Drainage Basin, Antarctica
Authors: Mae S. , Yoshida M.
Published: September 2017

Airborne radio echo-sounding was carried out in order to measure the thickness of the ice sheet in the Shirase Glacier drainage basin and map the bedrock topography. It was found that the elevation of bedrock was approximately at sea-level from Shirase Glacier to 100 km up-stream of the glacier and thereafter it was 500–100 m higher. Investigation of the echo intensity reflected from the bedrock indicates that at ice thicknesses less than 1000 m absorption was about 5.2 dB/100 m, but at greater ice thicknesses echo intensity did not depend upon the ice thickness but became approximately constant. Where ice thicknesses were greater than 1000 m in the main flow area of the Shirase Glacier drainage basin, the reflection strengths of about 9 dB were greater than outside the basin. Since the increase in echo intensity was considered to be due to the existence of water, the strong echo observed in the main part of the basin supported an hypothesis that the base of the basin was wet and the ice sheet was sliding on the bedrock.
Mass Balance of South-East Alaska and North-West British Columbia Glaciers from 1976 to 1984: Methods and Results
Authors: Pelto M.S.
Published: September 2017

The annual surface mass balance for 1983 and 1984 and the 10 year cumulative mass balances for 1975–85 were calculated for 60 south-east Alaskan and north-west British Columbia glaciers. At present, the mass balance is positive on nine, at equilibrium on nine, and negative on 42 glaciers. The ratio of glaciers with positive and equilibrium mass balance to glaciers with negative mass-balance has not changed significantly since 1946; however, the magnitude of negative balances has declined on 39 of the 42 glaciers.

The annual mass balance of south-east Alaska and north-west British Columbia glaciers cannot be measured on more than a few glaciers. This paper presents the methods and results for a mass-balance model using as input local weather records, Juneau Icefield field studies, and satellite imagery. The primary variable in mass balance from one glacier to another is the budget gradient. The budget gradient varies predictably according to three parameters: ocean proximity, surface slope, and valley width-valley height. The annual fluctuation of the budget gradient can be determined by examination of local weather records, determination of activity indexes, and delineation of the equilibrium-line gradient from the maritime to the continental part of each icefield. The latter two variables are determined using largely satellite imagery, keyed to topographic maps.

This procedure, where applicable, yielded mass-balance errors of ±0.16–0.22 m and 10 year cumulative mass-balance errors of ±0.08–0.15 m.
Large-Scale Patterns of Snow Melt on Arctic Sea Ice Mapped from Meteorological Satellite Imagery
Authors: Scharfen G. , Barry R.G. , Robinson D.A. , Kukla G. , Serreze M.C
Published: September 2017

The seasonal progression of snow melt on the Arctic pack ice is mapped from satellite shortwave imagery (0.4–1.1 micrometers) for four spring/summer seasons (1977, 1979, 1984 and 1985). This provides the first detailed information on the temporal change of the ice surface albedo in summer and of its year-to-year variability. The average surface albedo of the Arctic Basin for the years investigated falls from between 0.75 and 0.80 in early May to between 0.35 and 0.45 in late July and early August. In the central Arctic, where ice concentration remains high and ponding on the ice is limited, the July albedo ranges from 0.50 to 0.60. Overall, melt progresses poleward from the Kara and Barents Seas and from the southern Beaufort and Chukchi Seas, with the melt fronts meeting on the American side of the Pole. There are substantial year-to-year differences in the timing, duration and extent of the melt interval. The progression of melt in May and June of the earliest melt year (1977) was about 3 weeks ahead of the latest year (1979). By late July, the central Arctic was essentially snow free in 1977 and 1979, but more than 50% snow covered in 1984. Although limited in extent, our data base suggests relationships between snow melt and Arctic surface air temperatures in spring, spring cloudiness and the extent of late summer ice.
Use of Remote-Sensing Data in Modelling Run-Off from the Greenland Ice Sheet
Authors: Thomsen H.H. , Braithwaite R.J.
Published: September 2017

Run-off modelling is needed in Greenland to extend the short series of measurements. However, the delineation of hydrological basins on the Greenland ice sheet is difficult because of the lack of information about surface and subglacial drainage patterns. Low Sun-angle Landsat data have been used for mapping local surface features which has led to an improvement in basin delineations and thereby run-off simulations. Work is now in progress to map subglacial topography by electromagnetic reflection (EMR) from a helicopter. This information will be used for calculating hydraulic potentials within the basin and to assess the possibilities of future changes in drainage-basin delineation.