bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of surface perturbations on snow-slope stability
Authors: Conway H. 
Published: September 2017

Measurements and observations by others indicate that a potential slab avalanche consists of a relatively cohesive slab of snow overlying a thin weak layer that coniains flaws where locally the shear stress from the overburden is not fully supported. Under favorable conditions, snow will shear strain-soften, which provides the basis for applying a slip-weakening model to examine the size of flaw needed to initiate sub-critical crack propagation along the weak layer. Using typical values for snow properties, the model predicts sub-critical crack growth can initiate from a relatively small flaw well before the shear stress from the overburden approaches the peak shear strength at tin-bed. The occurrence of small flaws or imperfections in the basal layer would explain field measurements which usually indicate that avalanching occurs before the applied shear stress exceeds the shear strength at the basal layer.Widespread slab-avalanche activity often increases significantly soon after the onset of rain on new snow. Measurements of temperature and mechanical properties show that only the upper 0.15 m or less of the slab has been altered at the time of avalanching; alterations at the sliding layer have not yet been detected. Results from the slip-weakening model indicate that the rain-induced alterations would reduce the size of flaw needed to initiate sub-critical crack growth by 10–20%. The observations and model results show clearly the importance of the slab properties; it is evident that both the slab and the weak layer act together to control slope stability. A further implication is that the stability of freshly deposited snow is often close to critical, because a relatively small surface perturbation is often sufficient to cause avalanching. This is not surprising, because it is well known from field observations that new snow on slopes should be treated with caution.
Tentative investigations on surface hoar in mountain forests
Authors: Höller Peter 
Published: September 2017

This paper deals with air temperature, net-radiation and relative-humidity measurements which we performed in Austria in different zones of mountain forests in recent years. Our aim using such measurements was to approximate the general conditions for the formation of surface-hoar layers in low-density forest stands near the timber line. These layers are a necessary condition for snow-slab release and avalanche formation.Our investigations showed that the total radiation balance was negative but less negative in a forest with a close canopy (on clear nights about −30 to −40 W m−2) than within a small clearing (6 m by 6 m). Moreover, the total radiation balance within the forest clearing was almost the same as that in an open field. There we measured −60 to −80 W m−2 on clear nights. Approximations of surface temperature (ts) showed that ts was below the dewpoint (tE) in an open field but did not reach tE in the forest; moreover, ts was very close to tE within the forest clearing. Water-vapor flux was positive only in open terrain (i.e. condensation between 0.1 × 10−6 and 0.9 × 10−6 kg m−2 s −1 and evaporation occurred within the clearing and in the forest.
Comparison between experiment and computer modelling of plane-strain simple-shear ice deformation
Authors: Wilson C.J. L. , Zhang Y. 
Published: September 2017

AbstractAn examination of both experiments and computer models of polycrystalline ice undergoing a simple shear suggests that there is good agreement. The model has correctly reproduced the deformational and microstructural features caused by glide on (0001) in the ice aggregates. This success is particularly prominent for those ice grains with a lattice orientation suitable for hard or easy glide or kinking, and where there is a sub-horizontal с axis and a larger grain-size. A limitation may be that the model cannot explicitly simulate recrystallization and grain-boundary migration, which are two other important processes operating jointly with glide in experimentally deformed ice. However, through the use of the models, it is possible to show how kinematic factors can control the processes of recrystallization. The localization of recrystallization in the polycrystalline ice aggregate is determined by the stress and strain variations between neighbouring grains.
A glaciological model of the Younger Dryas event in Scandinavia
Authors: Fastook James L. , Holmlund Per 
Published: September 2017

AbstractA finite-element method solution of the continuity equation is used to investigate complex features of the Younger Dryas period. By comparing results of the model with field evidence, we conclude that the climatic event responsible for the Younger Dryas stillstand was probably short (less than 500 years). The assumption of a general sliding condition for elevations below 100 m, with an enhanced sliding zone through the center of the Baltic and Gulf of Bothnia, yields broad agreement for marginal positions in Sweden and Finland during a simulated termination. A stillstand near the Younger Dryas moraine position is attained with a climatic equilibrium-line altitude (ELA) depression of 600 m for a time period of 500 years. Agreement of simulated behavior with observed behavior is less consistent in the more maritime western Sweden and western Norway.
Hydrology of a segment of a glacier situated in an overdeepening, Storglaciären, Sweden
Authors: Leb. Hooke Roger , Pohjola Veijo A. 
Published: September 2017

AbstractTracer experiments, and water-level observations made while drilling 47 boreholes in an overdeepened section of Storglaciären, have demonstrated that nearly all of the water passing through this part of the glacier moves in englacial conduits. Much of the viscous energy dissipated by subglacial water flowing up an adverse bed slope out of such an overdeepening may be needed to warm the water to keep it at the pressure-melting point. If the adverse slope is sufficiently steep, freezing may occur within the conduits. The possibility for enlargement of conduits by melting is thus limited and water pressures become high. We infer that this, combined with possible blocking of conduits by freezing, forces the water to seek englacial pathways.The frequency with which englacial conduits are encountered during drilling suggests that there are several hundred of them in any given cross-section of the glacier. Consequently, each must carry a small fraction of the total discharge, say ∼ 10−3 m3 s−1. Tracer experiments suggest that flow rates in these conduits are < 10− m s−1, so conduit cross-sectional areas must be ∼10−2 m2, a size that is consistent with video observations in boreholes. The observed mean hydraulic gradient through the overdeepening is ∼0.04. If the conduits were of uniform cross-sectional area, the roughness implied by these figures would be unreasonably high and water pressures in them would be lower than observed. Thus, we hypothesize that conduits are locally constricted to only a small fraction of their average cross-sectional area.
Evolution of glaciation in the Pamiro-Alai mountains and its effect on river run-off
Authors: Konovalov V. G. , Shchetinnicov A.S. 
Published: September 2017

AbstractThe aim of the present research is to evaluate changes in the glacierized area, glacier-water resources and glacial run-off during the last 25–30 years. The prevailing process of degradation has resulted in a 16% diminution of the glacierized area in Gissaro-Alai and 11% in the Pamirs. The ratio between the advancing, stationary and retreating glaciers in the Gissaro-Alai mountains is 1:5:17, and the one in the Pamirs is 1:1:4. Moraine-covering of the glaciers has increased from 8 to 11 % in the Gissaro-Alai and from 6 to 11 % in the Pamirs. Ice-volume diminution of glaciers in the Gissaro-Alai is 17% and in the Pamirs it is 12%. The mean long-term annual volume of total glacial melting, glacial run-off and variation coefficients of these values in the river basins of the Pamirs and the Gissaro-Alai are described as functions of the altitudes of glacier termini, equilibrium lines and a new parameter, which characterizes the influence of the glacierized area distribution according to altitude on run-off. The data presented here indicate changes in mean annual volumes of glacier water yield in the river basins of the Pamirs and the Gissaro-Alai mountains, related to glaciation evolution in 1957–80.
Thermoluminescence in suspended sediment of glacier meltwater streams
Authors: Gemmell Alastair M.D 
Published: September 2017

AbstractTo determine the factors controlling natural levels of thermoluminescence (NTL) of fluvioglacially transported suspended sediment, samples were taken at hourly intervals from a meltwater stream emanating from Sólheimajökull in southern Iceland. The NTL of the samples were measured and compared with fluctuations in suspended-sediment load and in flow depth of the stream. It was found that the ratio of the 325°C and the 375°C regions of the NTL spectrum was more closely related to sediment load and flow depth than were the individual regions themselves. Analysis of the patterns suggests that NTL fluctuations are related to changes over time in the sources of sediment entrained by the stream. It is inferred that these changes relate to diurnal temperature cycles plus precipitation events. Such fluctuations raise doubts as to the validity of bulk sampling procedures in TL dating of Quaternary fluvioglacial sediments.
Historie retreat of Grand Pacific and Melbern Glaciers, Saint Elias Mountains, Canada: an analogue for decay of the Cordilleran ice sheet at the end of the Pleistocene?
Authors: Clague John J. , Evans S. G. 
Published: September 2017

AbstractGrand Pacific and Melbern Glaciers, two of the largest valley glaciers in British Columbia, have decreased over 50% in volume in the last few hundred years (total ice loss = 250–300km3). Melbern Glacier has thinned 300–600 m and retreated 15 km during this period; about 7 km of this retreat occurred between the mid-1970s and 1987, accompanied by the formation of one of the largest presently existing, ice-dammed lakes on Earth. Grand Pacific Glacier, which terminates in Tarr Inlet at the British Columbia–Alaska boundary, retreated 24 km between 1879 and 1912. This rapid deglaciation has destabilized adjacent mountain slopes and produced spectacular ice-marginal land forms. The sediments and land forms produced by historic deglaciation in Melbern-Grand Pacific valley are comparable, both in style and scale, to those associated with the decay of the Cordilleran ice sheet at the end of the Pleistocene (c. 14–10 ka BP). Rates of historic and terminal Pleistocene deglaciation also may be comparable.
Is the Longitudinal Profile of Storglaciaren, Northern Sweden, in Balance with the Present Climate?
Authors: Holmlund Per 
Published: September 2017

AbstractThe main perturbation in the mass balance of Storglaciären during the twentieth century was caused by a sudden 1°C increase in the summer mean temperature around 1910. Later perturbations of the climate have been of minor importance in relation to the mass balance. Annual field surveys suggest that the mass budget on Storglaciären has been in near balance for the last 15 years. Because of this major step-like change, we can establish the validity of theoretical models giving response times for Storglaciären of the order of 50 years. According to these models, Storglaciären could by now have reached a profile in balance with the present climate. To study this problem, the emergence velocity was calculated and compared with the net balance. The result shows that the emergence velocity either balances or exceeds the net balance for the entire tongue except for the lowermost part, where it decreases to about half of the net balance. A slight further recession of the front position would thus be expected with today’s climate.Calculated balance velocities also suggest that most of the present profile is close to a steady-state profile, if the mean annual sliding velocity is about 50% of the surface velocity. Lower sliding velocities would imply a thickening of the tongue and a thinning of the accumulation area during years of balanced mass budget.
Modelling Changes in Scattering Properties of the Dielectric and Young Snow-Covered Sea Ice at GHz Requencies
Authors: Drinkwater Mark R. , Crocker G.B. 
Published: September 2017

AbstractObservations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, N.W.T., Canada, were made during the winter of 1982. Detailed measurements of snow density, and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 8 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar back-scatter signatures of young sea ice. The results show that back-scatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from Synthetic Aperture or Side Looking Airborne Radar images.
Fish Antifreeze Proteins and the Creep of Polycrystalline Ice
Authors: Glen John W. , Ives David J. 
Published: September 2017

AbstractCreep curves obtained from the polycrystalline ice samples containing low concentrations of antifreeze glycopeptides (AFGPs) do not show the re-accelerating or tertiary creep that is found in pure ice samples. Previous work has shown that AFGPs inhibit grain-boundary migration in ice and the present results are consistent with this, as tertiary creep is associated with nucleation and growth of new ice grains.
Enhanced Radar Scattering From Water Inclusions In Ice
Authors: Bamber J.L. 
Published: September 2017

AbstractIt is believed that water-filled cavities on the scale of decimetres are present in a number of glaciers in Spitsbergen. The evidence for this hypothesis comes from airborne radio echo-sounding records collected by the Scott Polar Research Institute in 1983. The size of these cavities prevents the use of Rayleigh scattering theory and requires a more general analysis. Mie scattering theory is used to investigate the scattered power providing some unexpected results, the most significant of which is that for water bodies greater than approximately 0.25 m in radius the returned power from the volume illuminated is greater than that from a perfectly reflecting plane boundary.
Two-Dimensional Deformation Patterns in Sea Ice
Authors: Erlingsson Björn 
Published: September 2017

AbstractThe mechanical behaviour for the geometrical properties of two-dimensional deformation has been investigated. The Mohr formulation of failure, which is based on the concept of slip at the plane of weakness, is used in this study. It is shown that alteration of the shear stress τn at the plane of weakness requires self-similarity of features in deformation patterns. A general relationship between the angle of internal friction and the breaking angle of deformation patterns is derived. Using imagery data, this relationship is used to find the angle of internal friction from selected sea-ice deformation patterns. The value obtained for this angle is Φ = 15° ± 2° for deformation on a scale from 100 m to 100 km.
Early Discoverers XXXV: Descent of Glaciers: Some Early Speculations on Glacier Flow and Ice Physics
Authors: Walker J.C.F. , Waddington E.D. 
Published: September 2017

AbstractScheuchzer’s dilatation theory and Altmann’s rigid sliding theory were the first glacier-flow theories to receive serious scientific attention. When Agassiz began a research program at Unteraargletscher in 1839, he held several incorrect notions about glacier flow. Forbes understood the difficulties with the existing theories, and in the early 1840s he and Agassiz acquired motion, temperature, and structural data that were incompatible with the dilation and sliding theories but were suggestive of flow analogous to that of a viscous fluid. How an apparently brittle rigid solid like ice could flow became the central paradox requiring explanation. Some of the most able physicists of the mid-nineteenth century went through contortions in their largely misguided efforts to explain the viscous behaviour in terms of the known physics of rigid solids. Personality and speculation played a far larger part in their debates than we see in scientific discussions today.
The Mass Budget of the Lambert Glacier Drainage Basin, Antarctica
Authors: Allison Ian 
Published: September 2017

AbstractEstimates have been made of the mass budget of the total drainage basin of Lambert Glacier. These show a small but significant positive state of balance for the interior basin (the accumulation area up-stream of the major ice streams), and strongly suggest a positive balance for the Lambert Glacier system (the region of major ice streams, between the Amery Ice Shelf and the interior basin). The total mass flux into the interior basin is estimated as 60 Gt a−1. Results are presented from a number of ice movement stations established between 1972 and 1974 around the perimeter of the southern Prince Charles Mountains. These results, together with ice thicknesses from radio echo-sounding in the area, give a total mass outflux through the 2 000 m contour of 30 Gt a−1, implying a budget excess of a further 30 Gt a−1 over the whole interior basin. Results from velocity and ice thickness measurements give a mass discharge through a section near the junction of Lambert Glacier and the Amery Ice Shelf of 11 Gt a−1. Losses within the Lambert Glacier system proper account for a further 7 Gt a−1 and an overall mass excess of 12 Gt a−1 is estimated for the Lambert Glacier system. This present positive state of balance contrasts with geomorphological evidence from the southern Prince Charles Mountains of a large drop in ice level in recent geological time, and the ice surface in the area may now be building up after a major recession.
On the Computation of Heat Transfer Coefficients from Energy-Balance Gradients on a Glacier
Authors: Kuhn Michael 
Published: September 2017

AbstractThe turbulent flux of sensible heat in the energy balance of a glacier surface is assumed to be proportional to the temperature difference between the glacier surface and the atmosphere at the same level but outside the thermal influence of the glacier. The factor of proportionality between them is first explained in terms of friction velocity, roughness height, and stability function of the logarithmic wind and temperature profile. It is then derived from climatological records and measurements of the energy balance and its altitudinal gradients at Hintereisferner. Examples of the energy-balance components and their change with altitude are given for the entire ablation season as well as for short periods. The heat transfer coefficients derived have a mean value of 1.7±0.2 MJ m−2 d−1 K−1 (40 ± 5 ly d−1 K−1).
Supraglacial Debris of G2 Glacier in Hidden Valley, Mukut Himal, Nepal
Authors: Nakawo M. 
Published: September 2017

AbstractField investigations of supraglacial debris were carried out during the monsoon season in 1974 on G2 glacier near Tukche Peak in Hidden Valley, Mukut Himal, Nepal. The thickness of the debris layer was observed to increase down-glacier. Laboratory analysis, however, showed a decrease in particle size in the same direction. This decrease is explained in terms of mixing of particles contained in glacier ice with the original debris as melting proceeds. A simple relation between debris mass and glacier flow is introduced to explain the observed results.
Is Vertical Shear in an Ice Shelf Negligible?
Authors: Sanderson T. J. O. , Doake C. S. M. 
Published: September 2017

AbstractVertical shear stress in ice shelves cannot be precisely zero, since the upper and lower surfaces are generally not parallel. By performing stress balance on a vertical column in an ice shelf we calculate what its magnitude must be. This is done for an unconfined glacier tongue and for a confined bay ice shelf; first, using the assumption of constant temperature and density with depth, and secondly, using realistic data and profiles for Erebus Glacier tongue and for the Amery ice shelf. Shear stresses increase almost linearly with depth and are proportional to surface slope. For Erebus Glacier tongue the shear stress is at most 5% of the magnitude of the direct stress deviators and its action through the ice shell should result in differential movement of 1.8 cm a−1 between the top and bottom of the ice shelf. For the Amery ice shelf, the shear stress is at most 0.4% of the magnitude of the direct stress deviators and this should lead to differential movement of 2.5 cm a−1 between the top and bottom of the ice shelf. Shear stresses are therefore generally negligible in comparison with direct stress deviators and can be ignored when considering the overall dynamics of ice shelves. Differential movement is unlikely to be detectable.
The Mechanics of Drumlin Formation with Particular Reference to the Change in Pore-Water Content of the Till
Authors: Menzies John 
Published: September 2017

AbstractMost drumlins are composed of till that appears similar in all characteristics to non-drumlin till. Evidence, however, in the form of till layer sequences and from palaeomagnetic Koenigsberger ratios indicate that drumlin till may have a slightly higher pore-water content at the time of lodgement than nondrumlin till. In order that deposited till remains at the ice-glacier-bed interface to initiate drumlin formation, it must undergo rapid geotechnical changes whereby its pore-water content is dissipated thereby increasing the shear strength of the till. Two mechanisms of pore-water removal are possible. Firstly, pore water may be removed from localized patches within a mobile layer of till at the ice-glacier-bed interface, thus creating nuclei of higher-strength till around which deforming till may adhere. Secondly, removal of water initially from the thin water film at the base of a glacier may result in increased pressure melting of the ice leading to till melt-out and subsequent loss of pore water from the deposited till. The loss of water at the glacier bed may be either via permeable subglacial deposits or bedrock, or within subglacial depressions.
The Flow of Ice Over a Till Bed
Authors: Jones A. S. 
Published: September 2017

AbstractThis paper considers the contribution made to overall glacier flow by deformation of an unlithified bed. The flow pattern in deforming till beneath a glacier is determined for the case of a uniform ice slab resting on a uniform thick till bed. The results obtained show that, once the till is saturated, very little surplus water is needed to produce high velocities in the till near the ice−till interface, the interface velocity varying as the 5/2 power of the surplus water concentration. This sensitivity to water content suggests that this may be a mechanism inducing glacier surging.
Patterned Ground on an Active Medial Moraine, Jotunheimen, Norway
Authors: Ballantyne C. K. 
Published: September 2017

AbstractSorted circles and nets formed on the surface of the principal medial moraine on Storbreen, Jotunheimcn, Norway, are described. These consist of “islands” of coarse sand, granules, and small pebbles, surrounded by pebbles and cobbles and underlain by small domes of glacier ice. It is suggested that patterned ground formation on the moraine results from differential ablation in areas of thin (<200 mm) debris cover near the glacier snout, where melting is relatively rapid. It is unlikely that supraglacial patterned ground could survive deposition.