bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry
Authors: Rignot Eric , MacAyeal Douglas R. 
Published: September 2017

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.
Inter-borehole electrical resistivity imaging of englacial drainage
Authors: Hubbard Bryn , Binley Andrew , Slater Lee , Middleton Roy , Kulessa Bernd 
Published: September 2017

AbstractBorehole-based electrical resistivity surveys have the capacity to enhance our understanding of the structure of englacial drainage pathways in temperate ice. We summarize inter-borehole electrical resistivity tomography (ERT) as currently used in hydrogeological investigations and as adapted for imaging englacial drainage. ERT connections were successfully made for the first time in glacier ice, following artificial mineralization of borehole waters at Haut Glacier d’Arolla, Switzerland. Here, two types of electrical connection were made between boreholes spaced up to 10 m apart and drilled to depths of between 20 and 60 m. Most tests indicated the presence of resistively homogeneous ice with uniform bulk resistivities of ~108 - 109 Ω m. However, ERT was also successfully used to identify and characterize a hydraulically conductive englacial fracture that intersected two boreholes at a depth of ~ 13 m below the glacier surface. The presence of this connecting void was suggested by drilling records and verified by dual borehole-impulse testing. The reconstructed tomogram for these boreholes is characterized by a background ice-resistivity field of ~109 Ω m that is disrupted at a depth of ~13 m by a sharp, sub-horizontal low-resistivity zone (~10 4 Ω m). Inter-borehole ERT, therefore, has the capacity to image both uniform and fractured temperate glacier ice.
Basal-flow characteristics of a non-linear flow sliding frictionless over strongly undulating bedrock
Authors: Gudmundsson G. Hilmar 
Published: September 2017

AbstractThe flow field of a medium sliding without friction over a strongly undulating surface is calculated numerically. The results are used to elucidate the basal-flow characteristics of glacier flow and they are discussed with reference to known analytical solutions. Extrusion flow is found to become increasingly pronounced as the value of n, where n is a parameter in Glen’s flow law, becomes larger. For sinusoidal bedrock undulations, a flow separation occurs if the amplitude-to-wavelength ratio exceeds a critical value of about 0.28. The main flow then sets up a secondary flow circulation within the trough, and the ice participating in this circular motion theoretically never leaves it. The sliding velocity is calculated numerically as a function of the mean basal shear stress, the amplitude-to-wavelength ratio and the flow parameter n. For moderate and high slope fluctuations, the sliding velocity is significantly different from what would be expected from results based on the small-slope approximation.
Inversion of borehole-response test data for estimation of subglacial hydraulic properties
Authors: Stone Dan B. , Clarke Garry K. C. , Еllis Robert G. 
Published: September 2017

AbstractResponse tests are widely used in ground-water studies to assess the hydraulic properties of sub-surface water-flow systems. The simplicity of such tests also makes them attractive for investigation of subglacial hydraulic conditions. This paper describes a systematic, quantitative approach to the analysis of borehole-response test data. The approach uses the theoretical model of Stone and Clarke (1993), which describes water motion in a coupled borehole—subglacial flow system; this framework provides the basis for an inversion scheme that is focused on quantifying physical properties of the basal-flow system, as it is characterized in the theoretical model. The inversion procedure was applied to response-test data from Trapridge Glacier, Yukon Territory, Canada. Results of the inversions suggest that the subglacial drainage network can be described as a confined layer comprising coarse-sand-to fine-gravel-sized sediments, having a thickness of 0.1 – 0.3 m, and a hydraulic conductivity of about 5 × 10−4ms−1. Based on the water-drainage rates from boreholes, as they connect with the subglacial water-flow system, specific storage of the sediment layer was estimated to be approximately 1 × 10−4m−1. Further consideration of subglacial water-flow conditions suggests that connection drainage test results may tend to underestimate specific storage of the overall glacier substrate.
Avalanche frequency and terrain characteristics at Rogers’ Pass, British Columbia, Canada
Authors: Smith M.J. , McClung D. M. 
Published: September 2017

AbstractThe frequency of avalanches at a given location is the primary variable for calculating the risk as input to zoning applications and decisions about avalanche-control options. In this paper, we present an in-depth study of avalanche frequency using an extensive data base of avalanche-occurrence records from Rogers’ Pass, British Columbia (43 avalanche paths; 24 years of records). This study, the first of its kind for high-frequency avalanche paths, yields the result that the frequency of avalanches may be described by a Poisson distribution. Study of the relationship between terrain variables and precipitation estimates shows that avalanche frequency is significantly correlated with path roughness, 30 year maximum water equivalent, east-west location from Rogers’ Pass summit, wind exposure and run-out zone elevation and inclination. With the length of avalanche-occurrence records and quality of the data, we believe our study is the most comprehensive in existence about avalanche frequency and its relation to terrain variables.
A Notch-Strengthening Effect in Fresh-Water Ice
Authors: Nixon Wilfrid A. , Schulson Erland M. 
Published: September 2017

AbstractTensile tests have been performed on notched and unnotched cylindrical samples of randomly oriented polycrystalline ice of controlled grain-size (between 2.2 and 7.3 mm) at a loading rate of 100Pa s−1 and at a temperature of −10°C In the notched samples, the notch-root diameter was 80% of the base diameter. A notch-strengthening effect was observed in the large-grained ice, with fracture stresses being up to 50% higher than that for unnotched samples of the same grain-size. This notch-strengthening effect diminished as grain-size decreased, disappearing at a grain-size of ≈3 mm.The notch-strengthening effect is explained in terms of the triaxial stress constraint at the notch root. This triaxial constraint results in a change in the controlling mechanism of fracture from crack propagation in the unnotched samples to crack initiation in the notched samples.
Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada
Authors: Hawkins Fred F. 
Published: September 2017

AbstractThe fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.
Till Fabric and Deformational Structures in Drumlins Near Waukesha, Wisconsin, U.S.A.
Authors: Stanford Scott D. , Mickelson David M. 
Published: September 2017

AbstractDeep gravel-pit exposures reveal the distribution and structure of till and underlying sand and gravel in drumlins near Waukesha, Wisconsin. The subglacial sediment is interpreted to have moved laterally into the drumlin sites because the till thickens from the margin to the core of the drumlins, the stone orientation in the till is perpendicular and oblique to ice flow on the drumlin margins, and recumbent isoclinal folds occur in sand on the drumlin margins with axes parallel to the drumlin axes. The resulting accumulations of sediment presented obstacles to ice flow and were streamlined into the minimum-drag drumlin shape by erosion on the margins and by remolding of material in the core of the drumlins. These drumlin nuclei may have formed at spots where there was low effective stress on the bed. The subglacial sediment became mobile as a result of high pore pressure that may have developed as ground water and subglacial melt water were trapped behind a frozen bed at the ice margin. Under certain conditions, however, lateral sediment flow might also have occurred when the sediment was frozen.
A Preliminary Assessment of the Potential Application of Glaciochemical Investigations on Heard Island, South Indian Ocean
Authors: Spencer Mary Jo , Mayewski Paul A. , Berry Lyons Wm. , Hendy Martin R. 
Published: September 2017

AbstractAnalyses of fluoride, chloride, sodium, sulfate, bromide, nitrate, and iron from a 3 m snow pit on Heard Island, collected at an elevation of 2450, m are used to assess the potential of glaciochemical studies on. Heard Island glaciers. Sources for the chemical species are identified and, in particular, chloride, sodium, and sulfate are found to be useful seasonal indicators. The total record measured is believed to be less than one mass-balance year.
On the Analysis of Longitudinal Stress in Glaciers
Authors: McMeeking R.M. , Johnson R.E. 
Published: September 2017

AbstractIn the standard solution for the stresses in a glacier or ice sheet obeying Glen’s law, the down-slope component of the weight is supported by the basal shear stress, and the longitudinal deviatoric stress is second order. However, it has been found necessary to account for the longitudinal stress gradient when relating surface to bed topography with empirical data. In addition, during rapid stretching of the glacier, perhaps during a surge, the longitudinal stress gradient becomes comparable to or larger than the shear stress, and the standard solution is not entirely valid. In this paper, we consider the analysis of the stresses and strain-rates in a glacier when the longitudinal deviatoric stresses are comparable to the basal shear stresses. In some circumstances the down-slope component of weight is not borne completely by basal shear stress to leading order and some of the weight is shifted to the longitudinal deviatoric stress gradient. This case has also been examined. The results are used to obtain expressions for basal shear stress in terms of glacier thickness, slope, surface strain-rate gradient, and ice properties.
Medial Moraines of the Haut Glacier D’arolla, Valais, Switzerland: Debris Supply and Implications For Moraine Formation
Authors: Gomez B. , Small R. 
Published: September 2017

AbstractThe Haut Glacier d’Arolla displays three medial moraines: an ablation-dominant moraine east of the glacier centre line, an ice-stream interaction moraine west of the glacier centre line, and a medial-lateral supraglacial moraine complex along the western margin of the glacier. The eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus; this debris is derived from rock falls at the glacier head-wall, and follows a low-level transport path through the glacier. The western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2.6 km from the snout, but it receives further increments of sediment from extensive longitudinal englacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa. The medial-lateral moraine complex is formed largely by rock falls from the western valley wall, but is also nourished by a debris layer developed at the base of the small tributary Glacier de la Mitre. This layer crops out at the eastern margin of the re- sultant inset ice stream, and releases more rounded, abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin.
A Jökulhlaup Near Søndre Strømfjord, West GreenLand, and Some Effects on the Ice-Sheet Margin
Authors: Sugden David E. , Clapperton Chalmers M. , Knight Peter G. 
Published: September 2017

AbstractOn 19 and 20 August 1984, an ice-marginal lake drained through a subglacial tunnel beneath the ede of the Greenland ice sheet, discharging about 22.3 × 106 m3 of water in less than 19 h. The event, which may occur annually, modified ice-margin dynamics at the lake site and along a 3 km stretch of ice margin 11 km down-stream.
On the Long-Term Behaviour of Glacial Ice under Moving Traffic Load: A Case Study
Authors: Vombatkere S. G. 
Published: September 2017

AbstractA Bailey bridge built on a permanent ice body at an altitude of 5580 m above mean sea-level has been carrying regular traffic of 7 tonne motor vehicles for over 2 years. The problems posed by the ice body, its behaviour under the load of the bridge and traffic, its summer and winter behaviour, and the problems posed in the construction and maintenance of the bridge are studied and discussed.
The thermodynamic predictability of sea ice
Authors: Grumbine Robert W. 
Published: September 2017

AbstractStatistical analyses and model experiments suggest that the sea-ice cover is predictable weeks to months in advance. As such, it is one of the most highly predictable components of the climate system. The thermodynamic mechanisms by which this predictability can be realized are examined. It is found that the predictability is dependent on the differential growth/decay of sea ice as a function of thickness. In winter or year-round, for thin ice, the growth/decay rates are a strong function of thickness, which gives a relatively short period of predictability, though still long compared to the atmosphere. In summer, or year-round for thick ice, growth/decay rates are only weak functions of thickness and the period of predictability is comparatively long.
The character, structure and origin of the basal ice layer of a surge-type glacier
Authors: Sharp Martin , Jouzel Jean , Hubbard Bryn , Lawson Wendy 
Published: September 2017

AbstractThe basal ice layer of surge-type Variegated Glacier, Alaska, appears to have formed by a combination of (i) open-system freezing of subglacial meltwaters over both rigid and unconsolidated substrates; (ii) apron over-riding during surge-induced glacier advance; (iii) incorporation of glacier ice by recumbent folding, thrust-faulting and nappe over-riding during down-glacier propagation of a surge front; and (iv) post-formational metamorphism involving recrystallization, partial internal melting and squeezing out of meltwaters and dissolved gases. Structural evidence and the characteristics of debris entrained in ice facies formed by basal freezing suggest that the layer includes a lower element formed under surge conditions and an upper element formed during the quiescent phase of a surge cycle. The lower element is depleted in comminution products and enriched in medium gravel, while the upper element contains comminution products but virtually no medium gravel. This distinction is attributed to the efficiency of bedrock fracture and meltwater flushing of comminution products under surge conditions. The basal ice layer thickens from <1 m to >13 m down-glacier in a manner consistent with the magnitude of horizontal shortening induced by the 1982–83 surge. Thickening is largely tectonic in origin, and the style and intensity of folding and thrust faulting change down-glacier as the magnitude of horizontal shortening increases. Tectonic processes associated with the down-glacier propagation of surge fronts therefore appear to be capable of creating thick basal ice layers which allow extensive supraglacial sedimentation of subglacially derived debris.
Numerical avalanche prediction: Kootenay Pass, British Columbia, Canada
Authors: Mcclung D. M. , Tweedy John 
Published: September 2017

AbstractA numerical avalanche-prediction scheme was developed for highway applications at Kootenay Pass, British Columbia. The model features parametric discriminant analysis using Bayesian statistics to predict avalanche occurrences. Cluster techniques are then employed in discriminant space to analyze avalanche occurrences by the method of nearest neighbours. Extensive numerical testing of the model using an historical data base indicates that prediction accuracy may be 70% or better for both avalanche and non-avalanche time intervals.
Instruments and Methods: Diamond wire-saw cutting technique for investigating textures and fabrics of debris-laden ice and brittle ice
Authors: Tison J.-L. 
Published: September 2017

AbstractThis paper presents an original method for sampling special ice types like debris-rich ice or brittle ice that cannot be prepared using the standard band-saw/microtome procedure. The general working principles of the diamond wire-sawing technique are explained, and special adaptations for ice-cutting, thick-sectioning and thin-sectioning are discussed.
Glaciological Reconnaissance of an Ice Core Drilling Site, Penny Ice Cap, Baffin Island
Authors: Holdsworth G. 
Published: September 2017

AbstractA site situated close to the main divide of the Penny Ice Cap, Baffin Island was occupied in 1979 for the purpose of determining the suitability of this ice cap for providing proxy climatic data and other environmental time series for a span of 104 a. A 20 m core was extracted and analysed for stable oxygen isotopes, tritium concentration, pH, electrolytic conductivity, major ion concentrations, and particulate concentration. An adjacent dedicated shallow core was analysed for pollen content to determine if a significant seasonal variation in the pollen rain existed. From these measurements, and from the observations made on the stratigraphic character of the core, the mean net accumulation rate over the approximately 30 year period covered by the core is found to be about 0.43 m water equivalent per year. This is in agreement with a single value determined 26 years earlier at a nearby site (Ward and Baird, 1954). The mean annual temperature in the bore hole was found to be close to −14.4° C, possibly some 2–5 deg warmer than the expected mean annual surface air temperature at the site. This difference is due to the expulsion of latent heat upon freezing of melt water at depth in the snow-pack which gives rise to the many ice layers observed in the core. The percentage thickness of ice layers per year may be correlated with summer temperatures.Total ice depths were measured using a 620 MHz radar echo-sounder. In the vicinity of the divide, over an area of 1 km2, the ice depths vary from about 460 to 515 m. These values compare favourably with values determined from an airborne radar depth-sounding flight carried out over the ice cap by a joint U.S.–Danish mission operating out of Søndre Strømfjord, Greenland. The data suggest that the ice-cap divide would be a worthwhile location to deep core drill with an expected useful coverage of at least the Holocene period.
Englacial Deltaic Sediments as Evidence for Basal Freezing and Marginal Shearing, Leirbreen, Southern Norway
Authors: Harris Charles , Bothamley Keith 
Published: September 2017

AbstractA frozen englacial band of current-bedded silts, sands, and gravels were observed close to the snout of the temperate glacier Leirbreen. Little-disturbed sedimentary structures indicated a deltaic origin, the lack of disturbance showing that the sediments were frozen prior to their incorporation by the glacier and did not suffer shearing during glacial transport. It was concluded that they accumulated originally in a subglacial pool when the glacier was more extensive than today. Subsequent thinning of the glacier during recession allowed penetration of winter cooling to the base and freezing of subglacial sediments. The resulting layer of frozen sediment was protected from summer thawing by the overlying glacier and might therefore have been subject to further increase in thickness during successive winters. Incorporation of the frozen sediment band into the glacier resulted from compressive flow against the marginal zone of cold-based ice, leading to the development of thrust planes which penetrated through the glacier and into the frozen subglacial material. Shearing along such a thrust plane immediately below the frozen sediment layer, brought it through the glacier to the surface in a relatively undisturbed state.