bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short-period observations of speed, strain and seismicity on Ice Stream B, Antarctica
Authors: Harrison W. D. , Echelmeyer K. A. , Engelhardt H. 
Published: September 2017

AbstractThe speed of Ice Stream B, Antarctica, was measured twice a day-over a 1 month study period, and found to be steady at about the ±3½% level, the sensitivity of the measurements. The vertical strain was measured at three sites over a 1 year period at 1 h intervals with sensitivities of 2 or 0.2 ppm. The strain rate varied on all time-scales. Events of high strain rate were observed, but never at more than one site at a time. They can probably be understood in terms of local modification of the strain field associated with crevassing. Diurnal variation in strain rate was observed at one and possibly two sites during two summers. The seismicity was measured at all three sites, and diurnal and seasonal variations were prominent at all, the seismicity being much more intense in winter. Several possible causes of the diurnal variations in strain and seismicity are considered: thermal and atmospheric effects, and the effects of tides in the Ross Sea.
Laterally varying basal conditions beneath ice Streams B and C, West Antarctica
Authors: Atre Shashank R. , Bentley Charles R. 
Published: September 2017

AbstractThe study of the phase of reflections of Ρ waves off the base of Ice Streams Β and C, and Ridge BC, indicates that acoustic impedances of the beds of both ice streams vary laterally. In some places, the impedance is higher than in the ice (a high-impedance bed) and in some places it is less (a low-impedance bed). The estimated impedances in a dilated bed (porosity 0.4) and in a model of the lowermost ice that takes into account the relatively low P-wave speed in ice at or very near the melting point are nearly the same. Whether the impedance in the bed is greater or less than in the ice could depend on minor changes in the nature of the sediments composing the bed, or the physical state of the bed (e.g. porosity) that could occur laterally. Lateral variations of this kind provide a ready explanation for the observations on Ice Stream B. The bed under a substantial part of Ice Stream C that exhibits a low-impedance bed also must be dilated. The evaluation of the state of the bed under the rest of Ice Stream C and on Ridge BC requires further analysis, which is in progress.
Velocity pattern in a transect across Ice Stream B, Antarctica
Authors: Whillans I. M. , Jackson M. , Tseng Y-H. 
Published: September 2017

AbstractRepeat aerial photography is used to obtain closely spaced measurements of velocity and elevation over a complete transect of Ice Stream tributary B2, including the shear margins, the fast ice of the ice stream and several unusual features, as well as the UpB camp. Persistent features, mainly crevasses, are tracked to provide 1541 values of velocity and 1933 values of elevation. These are used to describe ice flow in the ice stream. Within the ice stream, the dominant velocity gradient is lateral shear. Crevasse patterns are studied in relation to measured velocity gradients. Crevasses intersect one another at acute angles, indicating that their origin is deeper than the depth to which crevasses penetrate. One feature within the ice stream seems to be a raft of stiff ice. Others are crevasse trains. Also, there are spreading ridges, perhaps due to upwelling ice. There is no evidence of large sticky spots within the studied transect, i.e. no steep surface slopes with associated surface stretching just up-glacier and surface compression down-glacier.
A conceptual model of solute acquisition by Alpine glacial meltwaters
Authors: Tranter Martyn , Brown Giles , Raiswell Robert , Sharp Martin , Gurnell Angela 
Published: September 2017

AbstractSolute acquisition by Alpine glacial meltwaters is the result of the coupling of different pairs of reactions, one of which usually involves dissolved gases. Hence, the availability of atmospheric gases to solution is an important control on the composition of glacial meltwaters. The chemical compositions of the two main components of the bulk meltwater, quick flow and delayed flow, are dominated by different geochemical processes. Delayed flow waters are solute-rich and exhibit high p(CO2) characteristics. The slow transit of these waters through a distributed drainage system and the predominance of relatively rapid reactions, such as sulphide oxidation and carbonate dissolution, in this environment maximize solute acquisition. Quick-flow waters are dilute, both because of their rapid transit through ice-walled conduits and open channels, and because the weathering reactions are fuelled by relatively slow gaseous diffusion of (CO2) into solution, despite solute acquisition being dominated by rapid surface exchange reactions. As a consequence, quick flow usually bears a low or open-system p(CO2) signature. Bulk meltwaters are more likely to exhibit low p(CO2) values when suspended-sediment concentrations are high, which promotes post-mixing reactions. This conceptual model suggests that the composition of both quick flow and delayed flow is likely to be temporally variable, since kinetic, rather than equilibrium, factors determine the composition.
Changes in the longitudinal profiles of glaciers during advance and retreat
Authors: Schwitter M. P. , Raymond C. F. 
Published: September 2017

AbstractThe pattern of elevation change along the length of glaciers caused by retreat from Neoglacial maximum to present is investigated and described in terms of a profile-shape factor f defined as the ratio of the average thickness change to the local thickness change at the present terminus. The factor f is relevant to estimation of the change in volume of a glacier in relation to its change in length and the response time to a change in climate. Thickness-change profiles on a selection of 15 mountain valley glaciers give f in the range 0.1–0.4 with an average of 0.28. The elevation changes are in all cases largest near the terminus and decrease headward more rapidly than a linear variation with distance that would correspond to f of 0.50, a value assumed to be characteristic in the past. The smaller values of f indicate reduced estimates of changes in volume versus change in lengths and smaller response times for glaciers. Total volume change for glaciers and ice caps (excluding ice sheets in Greenland and Antarctica) as estimated roughly by these means, is consistent with previous estimates from mass-balance measurements and supports the view that melting of these ice masses has made a significant contribution to sea-level change over the last century. The observed values of f do not explain an apparent discrepancy between alternative theoretical methods for estimating the response time of glaciers based on length and terminus velocity or based on the thickness and terminus-ablation rate. The discrepancy may be caused in part by the relationship between terminus velocity and ablation rate associated with strongly non-steady-state conditions during advance or retreat. The patterns of elevation change measured for short time intervals of a few decades or less correspond to a wide spread of profile-shape factor f from less than 0.1 to more than 1.2 indicative of transients in the short time-scale response.
Analysis of satellite-altimeter height measurements above continental ice sheets
Authors: Femenias P. , Remy F. , Raizonville R. , Minster J. F. 
Published: September 2017

AbstractIn order to estimate the accuracy of altimetric height measurements over ice sheets, an altimeter wave-form simulator has been developed, and different tracking methods have been tested. A large range of surface features, including large-scale and medium-scale features and micro-roughness have been taken into account for modeling of either surface-or volume-scattering. A large set of parameters affects the trailing edge of the radar wave form, so that re-tracking algorithms based on the detection of its leading edge provide better retrievals of the surface height than those based on the analysis of the whole wave form. A volume component is clearly present in the radar wave forms; its effect on the leading edge depends mostly on the snow grain-size (and therefore on the snow temperature) and on the pointing angle. However, on average, the induced error on the snow-surface height estimation should only be around 25 cm.
Ice/rock porous mixtures: compaction experiments and interpretation
Authors: KopystyńSki J. Leliwa , Maeno N. 
Published: September 2017

AbstractCompaction experiments on porous samples of granular ice and ice/rock mixtures were conducted at low temperature, primarily to obtain rheological data useful in modeling the internal structure and evolution of icy satellites of the giant planets. The data may also be of interest for studying Earth’s glaciers and the Martian polar caps.The samples tested were prepared from three types of ice: water, carbon dioxide and ammonia; three types of rock components were also used in the samples. The time-dependent compaction of samples a few centimeters in size was studied for a range of rock contents, pressures (2.2–17.7 MPa) and temperatures (140–261 K). An Equation (16), giving the compaction rate as a function of porosity, pressure, temperature and concentration of the rock component was fitted to the observed results. The presence of rock fragments strongly inhibits the compaction process.
Geographic and seasonal variations in the surface properties of the ice sheets by satellite-radar altimetry
Authors: Davis Curt H. , Zwally H. Jay 
Published: September 2017

AbstractGeosat-altimeter wave forms from the Greenland and Antarctic ice sheets are analyzed using an algorithm based upon a combined surface-and volume-scattering model. The results demonstrate that sub-surface volume-scattering occurs over major parts of the ice sheets. Quantitative estimates of geographic variations in the near-surface ice-sheet properties are derived by retracking individual altimeter wave forms. The derived surface properties correlate with elevation, latitude and microwave brightness-temperature data. Specifically, the extinction coefficient of snow obtained by this method varies from 0.48 to 0.13 m−1 over the latitudes from 65° to 72°N on the central part of the Greenland ice sheet and from 0.20 to 0.10 m−1 over a section of Wilkes Land in East Antarctica where the elevation increases from 2550 to 3150 m.Analysis of passive-microwave data over East Antarctica shows that the brightness temperature increases with elevation as the extinction coefficient decreases. Larger snow grain-sizes occur at lower elevations of the ice sheet because of higher mean annual temperatures. The larger grain-sizes increase the extinction coefficient of snow and decrease the emitted energy (brightness temperature) from greater snow depths. The passive-microwave data are also used to determine the average number of melt d year−1 (1979–87) for the central part of the Greenland ice sheet. For latitudes from 65° to 68.5° N, the average number of melt days decreases from 3.5 to 0.25 d year, whereas no melt events are observed for latitudes above 69°N over the 8 year period. Snow subjected to alternate melting and freezing has enhanced grain-sizes compared to that of dry snow. This accounts for the larger values and larger spatial variations of ke on the Greenland ice sheet compared to East Antarctica, where surface temperatures are never high enough to cause surface melting.
The Kinetic Friction on Snow and Ice
Authors: Kuroiwa Daisuke 
Published: September 2017

AbstractThis paper presents many experimental data of friction between a slider and snow or ice in relation to ski-ing and skating. Measurements of the kinetic coefficient of friction μk for a metallic or plastic-resin ring in contact with a snow surface were made using an oscillograph. The mechanism of this friction was analysed through oscillograms showing frictional resistance between a slider and a snow surface together with observations of the real contact area between the surface of the slider and snow grains. It was shown that friction at low sliding speeds caused plastic deformation within snow, but, when sliding velocity was increased, a stick-slip friction occurred accompanying fractures and abrasions of snow grains. Since the laboratory experiment of friction on snow is limited to a range of low sliding speeds, the measurements of μk for high sliding velocities were made by the use of practical skis. The value of μK for practical skis increased from 0.03 to 0.1 as the speed increased from for velocities 5 to 22 m/s.The measurements μk for skates were made using a specially designed device on skating rinks prepared both on natural lake ice and artificial ice. The temperature dependence of μk was studied for the blades of skates; μk showed a minimum value for both rinks around —1 to — °C, namely, 0.003 for the natural lake ice and 0.007 8 for the artificial rink ice.
Concentrated Loads on a Floating Ice Sheet
Authors: Nevel D. E. 
Published: September 2017

AbstractThe safe bearing capacity of a floating ice sheet is usually determined by limiting the maximum tensile stress which occurs under the load at the bottom of the ice sheet. If the size of the load distribution is large compared to the ice thickness, the thin plate theory predicts these stresses correctly. However, if the size of the load distribution becomes small compared to the ice thickness, the plate theory overestimates the stresses. In this case the ice sheet should he treated as a three-dimensional elastic layer.Previous investigators have solved the elastic-layer problem for loads distributed over a circular area, and have limited the results to the stress at the bottom of the ice sheet directly under the center of the load. In the present paper the stresses are evaluated at any radial position, and it is shown how these stresses approach those for the plate theory as the radial position becomes large. The solutions for the stresses are presented in integral form, as well as graphs from the numerical integration. These new results are significant for the superposition of stresses when two concentrated loads act near each other.Similarly for loads distributed over a rectangular area, the plate theory will overestimate the stresses if the dimensions of the load becomes small compared to the ice thickness. For this case integral solutions are presented for the stresses, and are evaluated directly under the center of the load.
On the Flow of Avalanching Snow
Authors: Heimgartner M. 
Published: September 2017

AbstractVariation of flow depth of a flowing avalanche caused by a change in the slope angle is examined using Bernoulli’s energy equation, used in hydraulics to determine a non-uniform steady flow. This equation is modified for a material with internal friction and a strongly curved track. The calculated flow depths are compared with those obtained by tests with a snow slide. In the flow model dry and turbulent friction are taken into account. Friction coefficients are estimated comparing calculated and measured flow depths. It appears that in wet snow they differ from those of dry snow. Finally, this model is used to calculate the runout distance of a natural avalanche.
Evaluation and Comparison of Statistical and Conventional Methods of Forecasting Avalanche Hazard
Authors: Föhn P. , Good W. , Bois P. , Obled C. 
Published: September 2017

AbstractPrincipal problems concerning the raw data and methodological limitations of statistical and conventional avalanche forecasting methods are summarized. The concepts of four statistical models based on multivariate data analysis, are outlined in a few words. In order to give an idea of the potential and quality of the different methods, test runs over two winters are discussed and a tentative store is established. Statistical models I and IV, together with the conventional forecast, attain a score of 70-80%, whereas statistical models II and III show a slightly poorer performance.
Alternate Methods for the Artificial Release of Snow Avalanches
Authors: Lachapelle Edward R. 
Published: September 2017

AbstractA series of devices have been developed and tested which are designed to initiate the release of snow avalanches by mechanically disturbing or altering the snow cover. These serve as substitutes for the conventional use of high explosives and artillery projectiles. Canister charged with an explosive mixture of gases can be fired electrically by remote control and recycled to fire again as needed. Air bags placed underneath the snow cover can be inflated with reasonably low pressure to disrupt and dislodge the snow cover. Energetic vibrators powered by compressed air can dislodge unstable snow under favorable circumstances. A polyethylene membrane placed on the ground surface of a sleep mountainside effectively inhibits the accumulation of snow by allowing new snow to slide off as fast as it accumulates. All of these methods have led to the practical release of avalanches but none appear a universal a universal solution to avalanche release in all circumstances. The gas exploder system is the most promising to date and is currently being installed for operational use.
Preliminary Observations of Acoustic Emissions Preceding Avalanches
Authors: Sommerfeld Richard A. 
Published: September 2017

AbstractSpontaneous emissions of noise were monitored in a snowpack on an avalanche track using three geophones. 30 Hz noise was recorded on magnetic tape for the whole avalanche season and 3 Hz noise for a short period of time. Periods before and during avalanches were associated with high noise, while periods of known stability were associated with low noise.
Artificial Release of Avalanches by Explosives
Authors: Gubler H. 
Published: September 2017

AbstractThe method of the artificial release of slab avalanches by explosives is investigated. The effect of a detonation on a seasonal snow cover is measured and discussed. The attenuation of the resulting stress waves as a function of the type of explosive used, the position of the charge relative to the snow surface, the snow-stratification profile, and the type of ground are determined in field experiments. The effective ranges of shots in potential fracture zones are estimated.
The Dynamics of Avalanching in the Khibins
Authors: Kotlyakov V.M. , Rzhevskiy B.N. , Samoylov V. A. 
Published: September 2017

AbstractResults of ten-year measurements of avalanche impact upon a large-sized installation are shown. The installation is equipped with 20 pressure sensors using the principle of the intrusion of a steel cone into a duralumin plate. The impacts of 30 dry avalanches with volumes from 100 up to 50 000 m3 are analysed. A maximum pressure at “a point" of 1 100 kN/m2 and a pressure of 650 kN/m3 averaged over the area of the installation (24 m2) were recorded. It is found that 75% of the impact energy is concentrated in the lowest 2 m of the installation. Proceeding from these data, and also taking into account that the thickness of an avalanche body amounts to 10-20 m at the moment of impact, we may conclude, that there is a “dense core" and an upper ’"high aerosol" part in an avalanche body.The use of slereo-photogrammetric surveys of moving avalanches revealed the “velocity depression" effect in the Khibin avalanches: Avalanche velocity decreases abruptly (by a factor 1.5 to 2) at the end of transit channel and then grows rapidly up to a maximum at the end of the avalanche cone. The greatest variations of velocity amount to 51 m/s.The data obtained prove the inefficiency of anti-avalanche filling dams, especially because of their negative role in the generation of disasterous air waves, whose pressure varies from 20 up to 150 kN/m 2.
Breakage of Ice Sheets by Underwater Explosions
Authors: Vittoratos E. , Charles M. E. 
Published: September 2017

AbstractWe have attempted to develop a theoretical understanding of the field experience on the destruction of floating ice sheets by explosives, by performing small-scale laboratory explosions and developing a theory based on the elastic plate. Glass spheres 4.5 × 10¯2 m in diameter and c. 4 × 10¯4 m thick were immersed in water underneath a floating ice sheet c. 2 × 10¯2 m in thickness. The air pressure was raised till the sphere burst at pressures around 15 atmospheres. A high-speed camera (up to several thousand frames per second) recorded the details of the explosion: the growth of the gas bubble and the corresponding deformation and failure of the ice. We observed radial and circumferential cracks develop within 2 ms of the bursting of the sphere.As a first step in the theoretical development, we have considered the response of an infinite elastic plate to impulsive pressure loading due to an underwater explosion. We have assumed potential, incompressible flow which is a valid approximation for the case of the above experiments and the analogous compressed-gas blasting in the field (Mellor and Kovacs, 1972). However the effects caused by the intense shock wave that is radiated by the detonation of a high explosive are thus not considered. We relate the maxima in the tensile stress with the crack pattern and the eventual damage, and have achieved qualitative agreement with the laboratory observations. The model does reproduce and clarify some aspects of the field data, in particular the role of the thickness (Mellor, unpublished); but it fails to relate the crater diameter to the weight of the explosive. It appears that at optimum blasting conditions with high explosives an incompressible-fluid, classical-plate-theory approach is inadequate.
A Study of Several Pressure Ridges and Ice Islands in the Canadian Beaufort Sea
Authors: Hnatiuk J. , Kovacs A. , Mellor M. 
Published: September 2017

AbstractThe environment conditions in the southern Beaufort Sea are described with special emphasis on pressure ridges and ice islands. Techniques for determining the geometric configurations and the physical and mechanical properties of sea-ice structures and ice islands are described. Profiles of pressure ridges were determined by surface surveys, drill-hole probes and side-looking sonar scanning. Multi-year pressure ridges with thicknesses up to 18 m and widths up to 110 m were examined in detail. The first-year ridge of 22 m thickness and 100 m width was studied. Results are given for several multi-year ridges and the first-year ridge. Information obtained from dives under the ice is also given. Corresponding data are given for grounded ice islands with particular attention being given to contact between the ice and sea bed. A 19 m thick ice-island fragment grounded in 13 m of water was one of several investigated. Measurements of temperature, salinity, tensile strength and compressive strength are given for ice taken from old pressure ridges and factors influencing the interpretation of test data are discussed. The data obtained in this study will be used in engineering design studies for off-shore structures for drilling and production of hydrocarbons from the Beaufort Sea area. Exploratory drilling in shallow water has already been carried out and off-shore drilling from drill ships is scheduled to commence in the study area during the open-water season of 1976.This paper will be published in full in a future issue of Journal of Glaciology.