bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recession of the southern part of Barnes Ice Cap, Baffin Island, Canada, between 1961 and 1993, determined from digital mapping of Landsat TM
Authors: Jacobs John D. , Simms Élizabeth L. , Simms Alvin 
Published: September 2017

AbstractChanges along the margin of the southern half of the 5900 km2 Barnes Ice Cap have been assessed using 1993 Landsat TM imagery in comparison with digitized 1:50 000 NTS maps based on 1961 photogrammetry. The average recession over the 183 km long southern perimeter was found to be at least 4 m a−1, with no significant difference between the southeast and southwest sectors. Viewed in conjunction with the sustained retreat previously reported for the northwest margin, these results indicate that a general reduction in the size of Barnes Ice Cap is occurring. The present retreat phase began under a regional climate warming in the late 19th to early 20th century period and continues, while the record of the ablation-season temperature since the mid-century has not shown any significant trend.
Meteorological controls on glacier mass balance: empirical relations suggested by measurements on glacier de Sarennes, France
Authors: Vincent C. , Vallon M. 
Published: September 2017

AbstractGlacial mass-balance reconstruction for a long-term time-scale requires knowledge of the relation between climate change and mass-balance fluctuations. A large number of mass-balance reconstructions since the beginning of the century are based on statistical relations between monthly meteorological data and mass balance. The question examined in this paper is: are these relationships reliable enough for long-term time-scale extrapolation? From the glacier de Sarennes long mass-balance observations series, we were surprised to discover large discrepancies between relations resulting from different time periods. The importance of the albedo in relation to ablation and mass balance is highlighted, and it is shown that it is impossible to ignore glacier-surface conditions in establishing the empirical relation between mass-balance fluctuations and climatic variation; to omit this parameter leads to incorrect results for mass-balance reconstruction in the past based on meteorological data.
Rheology of till beneath Storglaciären, Sweden
Authors: Hooke Roger LeB. , Hanson Brian , Iverson Neal R. , Jansson Peter , Fischer Urs H. 
Published: September 2017

AbstractIn order to study, in situ, the rheology of a deforming subglacial till, various instruments were emplaced in till beneath Storglaciären, Sweden. Boreholes were used to gain access to the till beneath about 100 m of ice. Tiltmeters provided an estimate of the shear strain rate in the till. Two other instruments yielded measures of till strength. In addition, water pressures were recorded in boreholes and in the till, a computer-controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag, based on a force-balance calculation.Tilt rates varied directly with effective pressure, so decreases in water pressure apparently increased the coupling between the glacier and the bed. Surface speed was either out of phase with tilt or varied independently of tilt. Thus, increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed; they were not a result of till deformation! Till strength varied directly with effective pressure, which is consistent with it being a Mohr – Coulomb, or frictional material. The devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed. This implies that the residual strength of the till is insensitive to strain rate. Thus, the appropriate constitutive equation for till rheology may be of the form:where k is a constant. This is consistent with experimental data reported in the geotechnical literature.
Determination of the Surface and Bed Topography in Central Greenland
Authors: Hodge Steven M. , Wright David L. , Bradley Jerry A. , Jacobel Robert W. , Skou Neils , Vaughn Bruce 
Published: September 2017

AbstractThe surface and bottom topography of the central Greenland ice sheet was determined from airborne ice-radar soundings over a 180 km by 180 km grid centered on the 1974 “Summit” site (lat. 72°18′N., long. 37°55′W.), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high-quality radar data were obtained, covering over 99'% of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft’s radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar-altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12% of the grid).The highest point on Greenland is at lat. 72°34′ N., long. 37°38′W., at an altitude of 3233 ± 6 m a.s.l. The ice surface at this point divides into three sectors, one facing north, one east-south-east, and one west-south-west, with each having a roughly uniform slope. The ice divide between the last two sectors is a well-defined ridge running almost due south. The ice is about 3025 m thick at the summit. Excluding the mountainous north-east corner of the grid, where the ice locally reaches a thickness of about 3470 m and the bed dips to about 370 m below sea-level, the maximum ice thickness, approximately 3375 m, occurs about 97 km south-south-west of the summit. The average bed altitude over the entire grid is 180 m and the average ice thickness is 2975 ± 235 m. The ice in most of the south-west quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sea-level. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10–15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the south-west basin would be suitable for the drilling of a new deep ice core.
Relationship Between the Development of Depth Hoar and Avalanche Release in the Tian Shan Mountains, China
Authors: Weilin Ma , Ruji Hu 
Published: September 2017

AbstractIn spring and winter, there is a considerable amount of solid precipitation in the western part of the Tian Shan mountains. Avalanches frequently occur here, and often endanger national economic construction and human life. Observation shows that the avalanche occurrences are closely related to the physical characteristics of the snow, especially to the development of depth hoar in the snow cover. The conditions for the development of depth hoar are determined by thickness of the snow cover, air temperature, ground-temperature regime, and the duration of negative temperatures. The results of this study have revealed that the optimum depth of snow cover for the development of depth hoar is about 80 cm in the Tian Shan mountains, and the mean maximum depth of the snow cover in this region is 78 cm. Therefore, depth hoar develops extraordinarily well. The thickness of depth hoar can reach more than 80% of the total snow-cover depth. That is one of the main reasons why avalanches still occur frequently under the conditions of a limited snow-cover depth in the western part of the Tian Shan mountains.
Avalanche Weather Forecasting at the Northwest Avalanche Center, Seattle, Washington, U.S.A.
Authors: Ferguson S.A. , Moore M.B. , Marriott R.T. , Speers-Hayes P. 
Published: September 2017

AbstractSince its inception in 1975, the Northwest Avalanche Center (NWAC) has developed and produced micro- and mesoscale weather forecasts to support avalanche forecast and control needs for the Olympic and Cascades Mountains of Washington and Oregon, U.S.A. This paper describes NWAC’s array of data, observational results, and analytical techniques that make “avalanche weather” forecasting possible. In addition, NWAC’s operational program and the general terrain and climate of the area are described. A sample forecast is also included.
Remote-Sensing Studies of Kvitøyjøkulen, an Ice Cap on Kvitøya, North-East Svalbard
Authors: Bamber Jonathan L. , Dowdeswell Julian A. 
Published: September 2017

AbstractAirborne 60 MHz radio echo-sounding data were collected over 250 km of flight track from an ice cap (Kvitøyjøkulen) on Kvitøya in north-eastern Svalbard. These were combined with Landsat imagery to provide ice-surface and bed topographic information and inferences about the thermal and climatic conditions on the ice cap. Quantitative analysis of radio-echo strength measurements and the existence of offshore plumes of sediment-laden melt water indicate significant basal melting and a warmer thermal regime than would be expected from the geographical location of the ice cap. Analysis of the dielectric absorption of radio waves by the ice and data from a recently recovered ice core from a neighbouring ice cap (Austfonna) suggest considerable anthropogenic contamination of the precipitation falling on Kvitøya, most probably originating from Eurasia.
In-Situ Tensile Tests of Snow-Pack Layers
Authors: Jamieson J.B. , Johnston C.D. 
Published: September 2017

AbstractDuring the winter of 1987–88, an average of seven tensile tests was made for each of 66 snow layers in the Rocky Mountains of western Canada. The precision of the mean strength for seven tests, expressed in terms of the coefficient of variation, was 15% with 90% confidence. Snow with a faceted micro-structure was approximately half as strong as partly settled or rounded snow of the same density. Notch sensitivity in the strength data and critical strains of 1% or less indicate that the test fractures were essentially brittle.
Towards Identification of Optimum Radar Parameters for Sea-Ice Monitoring
Authors: Kim Y. S. , Moore R. K. , Onstott R. G. , Gogineni S. 
Published: September 2017

AbstractVarious field experiments have shown that microwave radars can be used to distinguish multi-year from first-year ice, although optimum radar parameters are not yet fully defined.This paper presents the results from two theoretical models that, using selected physical parameters of sea ice, are able to predict the backscattering from multi-year and first-year ice under cold conditions. The possible ranges of the backscattering coefficient under various conditions (surface roughness, salinity, temperature, density, and air-bubble size) are calculated for multi-year and first-year ice by adjusting the parameters within the reported range of values.Although the calculations show no specific resonance that would favor any particular frequency or incidence angles, the results confirm the experimental findings that Ku- and X-band frequencies, and incidence angles greater than 30°, are better for distinguishing sea-ice types than lower frequencies.
δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications
Authors: Souchez R. A. , de Groote J. M. 
Published: September 2017

AbstractA freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.
On Supercooling and Ice Formation in Turbulent Sea-water
Authors: Omstedt Anders 
Published: September 2017

AbstractLaboratory data on supercooling and frazil-ice formation in sea-water are analysed using a boundary-layer model. The model is based on a turbulent channel-flow boundary-layer theory, in which buoyancy effects become important because of vertical gradients in temperature, salinity, and suspended frazil-ice crystals. The frazil-ice crystals are treated as thin uniform plates. By assuming a mean face diameter, a mean thickness, and a mean Nusselt number of 10−3 m, 10−4 m, and 4, respectively, the general experimental findings are well reproduced by the model.
Transfer of Basal Sliding Variations to the Surface of a Linearly Viscous Glacier
Authors: Balise Michael J. , Raymond Charles F. 
Published: September 2017

AbstractThe transfer of basal velocity anomalies to the surface of a glacier is investigated using a model of a planar parallel-sided slab (thickness H) of linear viscous rheology. Surface velocity parallel (us) and normal (vs) to the surface is calculated for various spatial distributions of basal velocity anomalies with components parallel (ub) and normal (vb) to the surface. Four scales of differing behavior can be identified depending on the spatial length L of the basal anomalies. At very short scales (L ≤ 1H) there is essentially no response at the surface. At short scales (1H ≤ L ≤ 5H), a basal anomaly ub induces a response in both us and vs. The spatial pattern of us is such that velocity peaks in us can be shifted from peaks in ub, and may differ in number. The amplitude of us is up to about 0.3|ub|. The amplitude of the cross-component effect vs may be greater than the amplitude of us. A basal anomaly vb induces a response in both vs and us. The pattern of vs is the same as the pattern of vb, and the amplitude of vs is up to about 0.7 |vb|. The amplitude of the cross-component effect us is less than the amplitude of vs. At intermediate scales (5H ≤ L ≤ 10H), results differ from the short scale in two respects; velocity peaks in us correspond with peaks in ub; and surface amplitudes are increased, except for cross-component effects for which surface amplitudes are of the same order as at the short scale. These cross-component effects at the short and intermediate scales show in particular that substantial anomalous surface-normal motions can be induced by deformation, even though the basal velocity anomaly is parallel to the surface. At long scales (10H ≤ L), the velocity anomaly at the surface is essentially the same as the anomaly at the bed. For all scales, the longitudinal strain-rate averaged over depth is larger in magnitude than the longitudinal strain-rate at the surface and, at the short scale, it may differ in sign, so that vs cannot be easily estimated from surface strain-rate. Although the simplifications of the model do not allow its rigorous quantitative application to field measurements, the results indicate the need for caution in interpreting surface-velocity variations in terms of basal velocity anomalies. It is important to establish the spatial pattern of surface motions for any chance of a confident interpretation in terms of basal motions.
Ice Avalanches: Some Empirical Information about their Formation and Reach
Authors: Alean Jürg 
Published: September 2017

AbstractA study intended to be mainly of practical use in the prediction of ice-avalanche hazards was carried out. About 100 ice avalanches, mostly from the Alps, were documented. Starting zones of these ice avalanches could be classified by using simple terrain characteristics. Ice avalanches from some starting zones at relatively low altitudes and with large, homogeneously inclined bedrock planes occur predominantly in summer and autumn. No such seasonal variation in frequency was found in connection with other types of starting zones occurring either at higher altitudes or involving abrupt changes of the bedrock’s gradient. One- and two-parameter models for the estimation of run-out distances of landslides and snow avalanches were tested for their use with ice avalanches. Introduction of the second (v2proportional) frictional parameter leads only to moderately improved accuracy in the prediction of run-out distances. For relatively short run-out distances (several hundred meters), an alternative method of estimation, based on terrain characteristics, is proposed.
Two-Dimensional, Time-dependent Modelling of an Arbitrarily Shaped Ice Mass with the Finite-Element Technique
Authors: Hodge Steven M. 
Published: September 2017

AbstractThe two-dimensional, time-dependent flow of an arbitrarily shaped ice mass can be successfully modeled with the finite-element technique on a small computer. Methods developed for automatically generating the mesh data greatly simplify the data preparation and optimize the numerical simulations. Using quadratic basis functions permits the flow to be approximated quite adequately by only two element rows (five nodes vertically). Mixed-order basis functions, however, must be used so that numerical oscillations do not set in, and the ends of the ice mass, where the thickness tends to zero, must be treated carefully. Time simulations to a steady-state condition are necessary to test such numerical models adequately.South Cascade Glacier, Washington, is currently close to equilibrium. A bedrock sill dominates the bed topography in the lower half of the glacier, rising to a height of about 20% of the ice thickness. This sill produces a maximum increase in the overall thickness of about 6–7% compared to what the thickness would have been if the sill were not present. Finally, this glacier does not appear to be sliding much, if at all, despite its maritime alpine environment. This could help explain the difficulties encountered when trying to measure sliding and basal water pressures on the same glacier (Hodge, 1979), or it could imply that drag exerted by the valley walls has a significantly greater effect than conventional shape-factor concepts imply.
The 1987–88 surge of West Fork Glacier, Susitna Basin, Alaska, U.S.A.
Authors: Harrison W. D. , Echelmeyer K. A. , Chacho E. F. , Raymond C. F. , Benedict R.J. 
Published: September 2017

AbstractA surge of West Fork Glacier, a temperate glacier in the Susitna Basin of the Alaska Range, began soon after the end of the 1987 melt season and terminated on 6 July 1988. Reconnaissance measurements of balance, elevation and speed had been made from 1981 to 1983. Daily measurements of surface speed at two points 9 km apart and of the characteristics of the stream draining the glacier were begun during the surge and continued through the following year. The maximum displacement of the ice during the surge was about 4 km; the maximum change in surface elevation was about 120 m. Between the time of the start of detailed observations on 12 February 1988 and the onset of a complex termination phase during the last month of the surge, the speed was almost constant, and the water discharge was totally free of turbidity, indicating that no basal water was escaping from the glacier. During the termination phase, sharp changes in speed occurred, almost simultaneously at the two observation sites; each deceleration event was accompanied by high sediment concentration and high water discharge. This behavior is similar to that observed on Variegated Glacier during its 1982-83 surge. The mechanism of triggering (related to surface water input and the disruption of the internal drainage system) and the cause of the fast motion were probably the same for both surges, even though there are substantial differences in size and mass-balance characteristics.
Borehole water-level variations and implications for the subglacial hydraulics of South Cascade Glacier, Washington State, U.S.A.
Authors: Fountain Andrew G. 
Published: September 2017

AbstractBoreholes were drilled in South Cascade Glacier to investigate the hydraulics of subglacial water flow. Results indicate that subglacial water pressures are generally close to local ice-overburden pressures and that a subglacial debris layer probably exists. Calculations indicate that the range of hydraulic conductivity of this layer is 10−7-10−4m−1. The borehole water levels generally increased during the ablation season and may be caused by a seasonal evolution in the permeability of the debris layer. Water in the debris layer drains to a subglacial conduit, the existence of which is inferred by large diurnal variations in the water level of one borehole. These levels commonly reached the bottom of the glacier, indicating near-atmospheric pressures in the conduit.
Ice triaxial deformation and fracture
Authors: Rist M.A. , Murrell S.A.F 
Published: September 2017

AbstractAn experimental investigation into the mechanical behaviour of polycrystalline ice in triaxial compression has been conducted using conditions generally favourable to brittle fracture and microcracking. Under triaxial stresses at high strain rate, ice failure occurs by abrupt shear fracturing, generally inclined at about 45° to the maximum principal stress. At −20°C, such failure is suppressed by the imposition of a small confining pressure, allowing a transition to ductile-type flow accompanied by distributed microcracking, but at —40°C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures (< 10 MPa), brittle strength is strongly pressure-dependent; above this it is pressure-independent. Evidence is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yielding. Ductile yield strength is found to be little influenced by confining pressure despite the inhibition of cracking that leads to greatly contrasting observed crack densities. Flow conforms to the well-known power law for ice withQ= 69 J mol−1andn= 4.2 over the temperature range −20° to −4-5° C Under these conditions, microcracking in ice appears to remain remarkably stable and non-interacting.
Calibration of the δ18O isotopic paleothermometer for central Greenland, using borehole temperatures
Authors: Cuffey Kurt M. , Alley Richard B. , Grootes Pieter M. , Bolzan John M. , Anandakrishnan Sridhar 
Published: September 2017

AbstractWe calibrate the δ18O paleothermometer for central Greenland using borehole temperatures, a thermal model forced by a measured δ18O record and a formal inverse technique. The calibration is determined mostly by temperature fluctuations of the last several centuries, including the Little Ice Age. Results are generally insensitive to model variables, including initial condition, basal boundary condition, parameterization of snow thermal properties, ice thickness and likely errors in temperature and isotope measurements. Results of this borehole calibration also seem to be in agreement with modern spatial gradients of δ18O and temperature. We suggest that calibrations of isotopic paleothermometers using borehole temperatures are a useful paleoclimate tool, because they are independent of spatial gradients and include the effects of prehistoric temperatures over ice sheets.