bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localized Basal Freezing Within George VI Ice Shelf, Antarctica
Authors: Pedley M. , Paren J.G. , Potter J.R. 
Published: September 2017

AbstractHobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads to in-situ freezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.
Drainage of the Austre Okstindbreen Ice-dammed Lake, Okstindan, Norway
Authors: Knudsen N. Tvis , Theakstone Wilfred H. 
Published: September 2017

AbstractObservations of the discharge, electrical conductivity, cationic content, and isotopic composition of glacier-river water indicate that drainage of the lake dammed at the margin of the glacier Austre Okstindbreen, Okstindan, Norway, is preceded by disruption of the glacier’s drainage system(s). Annual studies over a period of 12 years have demonstrated that intense storm precipitation, changes of ablation conditions, and the stage of development of drainage systems all may play a role in triggering drainage of the ice-dammed lake. Water temperature may influence the course of the outburst. The lake has drained on at least ten occasions in the last 12 years. Three of the events (1979, 1985, and 1986) occurred early in the summer, whilst melting of the winter’s snow cover was contributing substantially to glacier-river discharge: high basal water pressure and rapid sliding may have facilitated disruption of drainage conditions within the glacier. In 1982, the lake drained during a severe storm, in 1977 and 1984 shortly after a period of heavy rainfall. During the 1977 and 1984 events, water under pressure burst up through the glacier surface. The lake basin remained partly filled throughout one summer (1980): in-flow of water was balanced by out-flow into the glacier.
Seismic Evidence for a Weak Basal Layer During The 1982 Surge of Variegated Glacier, Alaska, U.S.A
Authors: Richards Mark A. 
Published: September 2017

AbstractWide-angle seismic reflections from a glacier bed are sensitive to the presence of subglacial water and to the mechanical strength of the basal zone. The phase of a compressional to shear (P-SV) converted wave is particularly sensitive to the shear coupling between the glacier and its bed. Both shear (SV) and compressional (P) reflections from the bottom of Variegated Glacier were obtained before the 1982–83 surge event using explosive sources, and the phases of these reflections (relative to the source) were positive as expected for an ice/bedrock interface. During surge, P-wave reflections from the deepest part of the glacier bed were phase reversed, while somewhat shallower P-wave reflections were not. SV reflections were not clearly observed during surge and cannot be interpreted with confidence, even though the experiments were designed to detect them using three-component geophones. The unexpected P-wave phase reversal might be explained by a thin, mechanically weak or fluidized basal debris layer during surge which acts as a strong seismic absorber and suppresses multiple reflections within the layer. However, the required amount of seismic attentuation in the layer seems unreasonably large. An alternative explanation requiring ∼4–8 m or more of water or water-saturated debris (without strong attenuation) is implausible.
Ice-shelf Response to Ice-stream Discharge Fluctuations: I. Unconfined Ice Tongues
Authors: MacAyeal Douglas R. , Barcilon Victor 
Published: September 2017

AbstractIce-stream discharge fluctuations constitute an independent means of forcing unsteady ice-shelf behavior, and their effect must be distinguished from those of oceanic and atmospheric climate to understand ice-shelf change. In addition, ice-stream-generated thickness anomalies may constitute a primary trigger of ice-rise formation in the absence of major sea-level fluctuations. Such triggering may maintain the current ice-rise population that, in turn, contributes to long-term ice-sheet stability. Here, we show that ice-stream-generated fluctuations of an ideal, two-dimensional ice shelf propagate along two characteristic trajectories. One trajectory permits instantaneous transmission of grounding-line velocity changes to all points down-stream. The other trajectory represents slow transmission of grounding-line thickness changes along Lagrangian particle paths.
Ice Flow and Mass Changes of Lewis Glacier, Mount Kenya, East Africa: Observations 1974–86, Modelling, and Predictions to the Year 2000 AD
Authors: Hastenrath Stefan 
Published: September 2017

AbstractThe study is based on an observation program since 1974, including the continuous monitoring of net balance during 1978–86. The 8 year vertical net-balance profile, characterized by negative values throughout and an increase of absolute amounts from the higher towards the lower elevations, defines the recent climatic forcing.A model is developed with a spatial resolution by 100 m wide bands, relating glacier morphology, ice flow, and mass economy, using as input ice thickness, surface slope, width of height contours, area of 100 m wide bands, volume flux, and net balance as a function of elevation. In 1 year time steps, the model calculates the changes in ice thickness and surface topography commensurate with the difference between net balance and longitudinal divergence of volume flux, and then the corresponding changes in surface slope, contour width, area of 100 m wide bands, volume flux, and net balance corresponding to the new surface elevations. This information serves as input for the next time step.The model was applied to the intervals 1974–78, 1978–82, and 1982–86, as training periods, to explore the diagnostics of ice flow and mass economy, and to ascertain the model performance in treating long-term evolution in glacier behavior. The experiments yielded a reasonable agreement between calculated and observed changes in ice thickness, velocity, and volume flux, over the three aforementioned 4 year periods of field monitoring. Two sets of prediction experiments beyond 1986 were then undertaken. The first used as input the observed 1978–86 vertical net-balance profile (a), and thus simulated the future evolution of the glacier given continuation of the recent climatic forcing. In the second set of experiments, the 1978–86 net-balance values were doubled to yield a more extreme net-balance profile (b), representing climatic conditions considerably more adverse to the maintenance of the glacier.Predictions are presented for the epochs 1990, 1994, 1998, and 2000. Given continuation of the recent climatic conditions (profile a), the following changes are anticipated from 1986 to the year 2000: a shrinkage of the volume from 4 to 1 x 106 m3; an area decrease from 25 to 17 χ 104 m2; a shortening of the glacier from 990 to less than 800 m; a slow-down of fastest ice flow from 2.5 to less than 1ma−1; a decrease of the maximum volume flux from 13 to less than 3 χ 103 m3 a−1; and substantial up-glacier displacements of the velocity and volume-flux maxima. Under more extreme negative net-balance conditions (profile b), the decay would be so greatly accelerated that Lewis Glacier may completely disappear well before the end of the millennium. This prospect is inherent in a possible change from recent climatic conditions.
Morphology and Dynamics of Ice Rises
Authors: Martin P. J. , Sanderson T. J. O. 
Published: September 2017

AbstractProfile surveys are presented of four ice rises on the east coast of the Antarctic Peninsula. On Butler Island velocity measurements were also made. The ice rises behave as miniature ice caps frozen to flat horizontal bedrock and provide a simple system for the study of laws of ice flow. Deformation is principally by shear through the ice mass. Velocity measurements provide a value of n = 3.13±0.52 for the flow law . Each ice rise is bounded on one side by ice shelf and on the other side by open sea. Towards open sea the profiles are found to agree well with steady-state theoretical profiles and they supply a value of for temperature – 13.5°C and stress range 0.5–1.3 bar. Towards ice shelf the profiles are elongated and they deviate from the theoretical profile. This may be due to compressive stress in the ice shelf causing migration of the grounding line down sloping bedrock. No significantly anomalous behaviour is found in the summit region.
The Creep of Ice, Geothermal Heat Flow, and Roosevelt Island, Antarctica
Authors: Thomas Robert H. , MacAyeal Douglas R. , Bentley Charles R. , Clapp James L. 
Published: September 2017

AbstractMeasurements of ice velocity, thickness, and surface topography on the large ice rise known as Roosevelt Island are consistent with Glen’s flow law, , for values of τ between 5 × 104 N m–2 and 1.4 × 105 N m–2, and there is no indication of a reduction in n at low stresses. If n = 3 there must be progressive softening of the ice towards the edge of the ice rise, and this probably represents the combined effects of warming and recrystallization leading to a fabric favoring shear. Assuming that near the centre of the ice rise, where the effects of recrystallization are probably negligible, the ice behaves in the same way as randomly-oriented polycrystalline ice, then the geothermal flux G in this area is approximately 0.06 W m–2. In the absence of measurements of deep-ice temperatures, the distribution of G across the ice rise cannot be determined. However, the simplest interpretation of the movement data requires:
(1)a linear increase in G from 0.05 W m–2 on the north-east side of Roosevelt Island to 0.07 W m–2 in the south-west, and(2)strain-rate enhancement, due to recrystallization, that increases outward from the centre of the ice rise to reach a maximum value of approximately two near the edges.The calculated values of G are larger than the world average, but this is consistent with the probably granitic core beneath Roosevelt Island. An increase in G of 0.02 W m–2 in a distance of 60 km would require an increase in granite thickness of about 5 km.
Glaciological Investigations of the Tropical Quelccaya Ice Cap, Peru
Authors: Thompson Lonnie G. 
Published: September 2017

AbstractGlaciological results of the continuing investigations of the Quelccaya ice cap located at lat. 13° 56’ S., long. 70° 50’ W., in the Cordillera Oriental of southern Peru are presented. Ice cores to a depth of 15 m have been retrieved from the summit dome (5650 m), middle dome (5543 m), and south dome (5480 m) and sampled in detail for microparticle, oxygen-isotope, and total-β-activity measurements. Results of these core analyses indicate that although the summit of this ice cap is only 300 m above the annual snow line and the firn is temperate, an interpretable stratigraphic record is preserved. The marked seasonal ice stratigraphy is produced by the marked seasonal variation in regional precipitation. High concentrations of microparticles and β- radioactive material occur during the dry season (May-August). Microparticles deposited during the rainy season are larger than those deposited during the dry season. On the Quelccaya ice cap the most negative δ18O values occur during the warmer rainy season (the opposite occurs in polar regions). The near-surface mean δ value of – 21‰ is remarkably low for this tropical site where the measured mean annual air temperature is – 3°C The seasonality of the microparticles, total β activity, and isotope ratios offers the prospect of a climatic ice-core record from this tropical ice cap.
Microwave Brightness of Polar Firn as Measured by Nimbus 5 and 6 ESMR
Authors: Chang A. T. C. , Choudhury B. J. , Gloersen P. 
Published: September 2017

AbstractThe microwave emission from a half-space medium characterized by coordinate dependent scattering and absorbing centers has been calculated by numerically solving the radiative transfer equation by the method of invariant imbedding. A Mie scattering phase function and surface polarization have been included in the calculation. Also included are the physical temperature profile and the temperature variation of the index of refraction for ice. Using published values of grain-size and temperature-profile data of polar firn, the brightness temperature has been calculated for the 1.55 cm and 0.8 cm wavelengths. For selected regions in Greenland and Antarctica, the results of our calculations are in reasonable agreement with the observed Nimbus-5 and Nimbus-6 ESMR data.
Pressure Waves in Snow
Authors: Brown R. L. 
Published: September 2017

AbstractA dynamic constitutive law is used to study the response of medium-density snow to shock waves. The results show good correlation between theory and experiment, except for low-intensity shocks which produce small permanent density changes. In this case the validity of the data is questioned, although further experimental work is needed to settle this question. The results of this work also partially explain why snow is so effective in absorbing energy associated with stress waves. This is felt to be due to the work-hardening characteristics of snow.
A Scanning Electron Microscope Examination of Subglacial Quartz Grains from Camp Century Core, Greenland–A Preliminary Study
Authors: Whalley W. B. , Langway C. C. 
Published: September 2017

AbstractSurface textures and angularity–roundness characteristics of quartz sand grains of till from the base of the Greenland ice sheet at Camp Century were examined with a scanning electron microscope. Two basic populations are revealed; an angular component, which shows grains with edge abrasion and attrition indicative of subglacial grinding, and a well-rounded component with the characteristics of aeolian transport. It is suggested that these two populations were mixed subglacially, the aeolian fraction having been produced at some stage before the ice sheet encroached over the area of their deposition.
A Process-Oriented Model for Simulating Avalanche Danger
Authors: Judson Arthur , Leaf Charles F. , Brink Glen E. 
Published: September 2017

AbstractA simulation process model is developed for rating avalanche danger for twelve east-facing avalanche paths loaded by westerly winds. The model simulates layer age and densification, snow depth, snow transport and deposition, formation of melt crusts, snow temperatures, temperature gradient metamorphism, and avalanche danger on a 6 h basis. Conditioned on avalanches alone, the model predicted avalanche potential on 86% of the 175 avalanche days during an eight-year period. It indicated avalanche potential 50% of the time on non-avalanche days. A sensitivity analysis is under way to improve model performance, and simulation of danger from additional avalanche samples is planned.
Credibility of Avalanche Warnings
Authors: Williams Knox 
Published: September 2017

AbstractAvalanche warnings can provide a valuable public service. To be effective, the warning program must inspire public confidence. Experience gained from the Colorado Avalanche Warning Program is used to develop guidelines for establishing and maintaining credibility. The topics discussed arc the requirements for a good forecaster, the working relationship between forecaster and field observers, relations with the news media and the public, and forecast accuracy.
A Study on High-Speed Avalanches in the Kurobe Canyon, Japan
Authors: Shimizu Hiromu , Huzioka Tosio , Akitaya Eizi , Narita Hideki , Nakagawa Masayuki , Kawada Kunio 
Published: September 2017

AbstractObservations and measurements were made of high-speed avalanches at Shiai-dani, the Kurobe canyon, to reveal their real features and properties, using strain-gauge-type load cells in measuring impact force and speed. A maximum impact pressure of 140 × 104 N m-2 was obtained, as well as data indicating the existence of a number of wave fronts, ranging in speed from 9 to 60 m s -1 inside an avalanche. Violent changes in atmospheric pressure ranging from -21 to +5 mbar were observed near its path when a high-speed avalanche passed by.
Empirical Calculations of Snow–Avalanche Run–out Distance Based on Topographic Parameters
Authors: Lied K. , Bakkehøi K. 
Published: September 2017

AbstractA method for calculation of “maximum” avalanche run–out distance based on topographic parameters only is described. 423 well–known avalanches have had their maximum extent registered. The average gradient of avalanche path (α–angle), measured between the highest point of rupture and outer end of avalanche deposit is used as description of avalanche run–out. The topographic parameters which determine α are described.A regression analysis of 111 avalanche paths based on 8 terrain parameters is performed, applying 26 independent combinations of these parameters as variables. The four best combinations of variables are used. These variables are: second derivative y’’ of avalanche slope described by a second–degree function, average gradient of avalanche track β, total vertical displacement of the avalanche H, and gradient of rupture zone θ.The equation has a correlation coefficient of 0.95 and standard deviation of 2.3°. This relationship makes possible a fairly accurate prediction of avalanche run–out distance.
The Acoustic Emission Response of Snow
Authors: St Lawrence William F. 
Published: September 2017

AbstractIn this work a model of the ultrasonic acoustic emission response in snow is developed. The model derived considers the acoustic emission response in snow as a function of stress and strain. It is suggested that the acoustic emission activity in snow is a quantitative indication of the creep rupture taking place in the material. The governing differential equation is developed; an example is then presented that considers the applicability of this equation to the release of certain types of avalanche.
Statistical Models of Snow Strength
Authors: Sommerfeld Richard A. 
Published: September 2017

AbstractSnow is variable in both time and space. Because of this fact, a complete understanding of snow strength must include statistical strength analyses. Two types of statistical strength theories are the series-element, or weakest-link theories and the parallel-element theories. In the case of snow in shear, Daniels’ (1945) parallel-element theory provides a quantitative explanation of the size and stress-rate relationships of snow, which are at least as accurate as presently available data. In the case of tensile tests, a combination of the two types of theories is proposed which also provides a quantitative explanation which is as accurate as present data. In each case large-volume, low-stress-rate strengths are predicted using small-volume, high-stress-rate data. More data are necessary to provide definitive tests of the proposed hypotheses.
Viscosity and heat transfer in fluidized snow
Authors: Maeno N. , Nishimura K. , Kaneda Y. 
Published: September 2017

AbstractFluidized snow was produced in a cold laboratory and its viscosity and heat transfer were studied. The viscosity of the fluidized snow was measured with a modified Stormer-type viscometer. It was found that the apparent viscosity decreased with increasing air velocity and decreasing particle diameter. Two mechanisms were suggested as producing the viscosity of the fluidized snow on the basis of the plot of the viscosity against the reciprocal of the air velocity.The heat-transfer coefficient was obtained by measuring the temperature of a cooled brass sphere suspended in the fluidized snow. The heat-transfer coefficient in the fluidized snow was three or four times larger than that in an air flow containing no snow particles. The increase was attributed to the enhanced turbulence of air flow and the collision of snow particles; the contribution of the latter was estimated to be 80 to 90% of the total increase due to the fluidization of snow. These results were also confirmed in an artificial blowing snow produced in a cold horizontal wind-tunnel by measuring the heat-transfer coefficient, wind velocity, and drift density.
Mechanical behaviour and structure of snow under uniaxial tensile stress
Authors: Narita Hidek 
Published: September 2017

AbstractThe mechanical behaviour of snow was studied at — 10°C under uniaxial tensile stress in a range of cross-head speed 6.8 × 10–8 to 3.1 × 10–4 ms–1 and snow density 240-470 kg m–3.It was found from the resisting force-deformation curves that the snow was deformed in two different ways: namely, brittle and ductile deformation at high and low strain-rates, respectively. The critical strain-rate dividing the two deformation modes was found to depend on the density of snow. In ductile deformation, many small cracks appeared throughout the entire specimen. Their features were observed by making thin sections and they were compared with small cracks formed in natural snow on a mountain slope.The maximum strength of snow was found to depend on strain-rate: at strain-rates above about 10–5 s –1, the maximum strength increased with decreasing strain-rate but below 10–5 s–1 it decreased with decreasing strain-rate.
Avalanche-Hazard Mapping and Zoning Problems in the Rocky Mountains, with Examples from Colorado, U.S.A.
Authors: Ives Jack D. , Plam Misha 
Published: September 2017

AbstractAvalanche-hazard mapping as a basis for land-use decision-making was not undertaken systematically in Colorado until 1974. Passage of Colorado House Bill 1041 required counties to map areas subject to snow avalanche, landslide, debris flow, and mountain flood at 1 : 24 000, and funds were provided. This legislation induced several approaches: work undertaken directly by the Colorado Geological Survey; private contract work; mapping by the Institute of Arctic and Alpine Research (INSTAAR) funded by a NASA research grant. This latter effort produced 37 individual 1 : 24 000 map sheets of Hinsdale, Ouray, San Juan, and San Miguel counties, San Juan Mountains. This emphasized problems of scale and degree of cartographic accuracy. Swiss, Austrian, and French experience, together with the actual Colorado mapping experience, facilitated further definition of problems facing the Rocky Mountains slates, both in terms of resolution of actual mapping problems, and of using such developing experience to influence the decision-making process.Two mapping attempts are described: (i) development of a combined hazard map for a mountain type area, indicating the difficulties of, and need for, combining hazard assessment of avalanche and other physical processes that frequently overlap; (ii) consideration of avalanche-zoning problems in a wilderness area.Finally, scale limitations and the need to define rigorously “hazard” are discussed. Definition of hazard must include consideration of recurrence interval, impact pressures in the run-out zone, and limitations of displaying this type of data on available topographic maps, all in relation to types of impact, i.e. to moving or stationary objects in relatively sparsely populated terrane. Additional critical needs facing Rocky Mountains states are itemized: (i) standardized mapping legends for different scales; (ii) establishment of an avalanche cadastre; (iii) systematic reporting of climax events; (iv) development of an historical archive; (v) public awareness; (vi) attention to legal aspects of the avalanche equivalent of the hundred-year flood, and its legal testing.