bluuebunny/crossref_metadata_2025 huggingface dataset:
Hinge-line migration of Petermann Gletscher, north Greenland, detected using satellite-radar interferometry
Authors: Rignot Eric
Published: September 2017

The synthetic-aperture radar-interferometry technique is used to detect the migration of the limit of tidal flexing, or hinge line, of the floating ice longue of Peter-mann Gletscher, a major outlet glacier of north Greenland. The hinge line is detected automatically from differential interferograms using a model-fitting technique based on an elastic-beam theory. The statistical noise of the model fit is less than 3 mm, and the hinge line is mapped with a precision of 30 m. Following automatic registration of multidate image data to a precision of 5m, hinge-line migration is subsequently detected with a precision of 40 m in the horizontal plane across the glacier width. The results show that the hinge line of Petermann Gletscher migrates back and forth with tide by ±70m, in excellent agreement with the migration calculated from ocean tides predicted by a tidal model combined with the glacier surface and basal slope measured by an ice-sounding radar. Superimposed on the short-term hinge-line migration due to tide, we detect a hinge-line retreat of 270 m in 3.87 years which varies across the glacier width by ± 120 m. The retreat suggests glacier thinning at a rate of 78 + 35 cm ice a−1. Coincidentally, an analysis of ice-volume fluxes indicates that the hinge-line ice flux of Petermann Gletscher exceeds its balance flux by 0.88±1km3 ice a−1, which in turn implies glacier thinning at 83+95cm ice a−1 in the glacier lower reaches. Both methods therefore suggest that Petermann Gletscher is currently losing mass to the ocean.
Measurement of temperature in a margin of Ice Stream B, Antarctica: implications for margin migration and lateral drag
Authors: Harrison W. D. , Echelmeyer K. A. , Larsen C. F.
Published: September 2017

Ice temperature was measured in and around the chaotically crevassed south margin of Ice Stream B, Antarctica, from 1992 to 1994. The temperatures at 30 m depth in the chaotic zone are about 12 K lower than in the adjacent uncrevassed ice, due to the ponding of cold winter air. At depths greater than 150 m, there is clear evidence of internal heating of the ice due to the large shear déformation rate in the marginal zone. Analysis of the depth of cooling below the crevasses and of the internal heating gives two pieces of information. First, over the last half century the lateral shear stress averaged 2.0 x 105 Pa in the top third of the margin and, second, the margin moved outward at an average rate of 7.3 m a−1. These values do not involve any assumptions about the How law of ice. The uncertainties are roughly 20%. The value of lateral shear stress indicates that the most of the drag on the ice stream is along its sides.
A theory of ice-sheet surges
Authors: Fowler A. C. , Schiavi E.
Published: September 2017

A simplified model of a two-dimensional ice sheet is described. It includes basal ice sliding dependent, on the basal water pressure, which itself is described by a simple theory of basal drainage. We show that this simple but sophisticated model predicts surges of the ice mass in realistic circumstances, and we describe these surges by solving the problem numerically. We also are able to describe some parts of the surge analytically. The numerical solution of the model is a delicate matter, and highlights pitfalls to be avoided if more complicated models are to be solved successfully.
Elevation, volume and terminus changes of nine glaciers in North America
Authors: Sapiano J. J. , Harrison W. D. , Echelmeyer K. A.
Published: September 2017

Nine glaciers in Alaska and Washington, U.S.A., originally mapped as part of the International Geophysical Year (IGY) in 1957—58, were re-mapped between 1993 and 1996, eight using airborne surface elevation profiling and the ninth using ground-based kinematic global positioning system methods. Elevation, volume and terminus changes were determined for the approximately 38 year period between the IGY mapping and the profiling, All nine glaciers showed substantial thinning at lower elevations; seven of the nine thickened at higher elevations. None of the glaciers had a significant net volume increase; two had close to zero change, and the others had a decrease. For the eight glaciers for which we could obtain quantitative information, the mean thickness change was -10 m with a large scatter, 8 m standard deviation. The volume and terminus changes had no clear geographic pattern, and no simple relationship between volume change and terminus advance or retreat was identified. The largest error in the estimated volume changes is due to map errors.
The structural glaciology of Kongsvegen, Svalbard, and its role in landform genesis
Authors: Glasser Neil F. , Hambrey Michael J. , Crawford Kevin R. , Bennett Matthew R. , Huddart David
Published: September 2017

Mapping of the structural glaciology of Kongsvegen, Svalbard, reveals evidence for four main deformational structures. These are stratification, longitudinal foliation, thrusts and crevasse traces. These structures are considered in terms of their contribution to debris entrainment, transport and subsequent landform development. Stratification is associated with small amounts of supraglacial debris that has been folded with flow-parallel axes; longitudinal foliation in places incorporates basal glacial sediments along folds with flow-parallel axes; and thrusts transport basal debris to the glacier surface. Crevasse traces are not significant in terms of debris entrainment. The entrainment of basal debris along longitudinal foliation is not a universally recognised process. At Kongsvegen this process is attributed to the development of a transposition foliation, in combination with incorporation of debris-rich basal ice or soft basal sediment in the fold complex. Mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as “foliation-parallel ridges” and that transverse ridges mark debris-bearing thrusts. The role of longitudinal foliation in landform development has never been documented in this manner. Although the preservation potential of such ridges may be limited, recognition of foliation-parallel ridges in the Pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses.
Physical and chemical studies in the region of the southern slope of Mount Elbrus, Caucasus
Authors: Bazhev A. M. , Rototaeva O. , Heintzenberg J. , Stenberg M. , Pinglot J. F.
Published: September 2017

For glaciological and meteorological reasons Mount Elbrus, Caucasus, was chosen as a site for physical and chemical pilot studies of ice cores. This study was the first step towards systematic studies of impurities in glacier ice on Mount Elbrus. In 1900 two ice cores, each 17 m deep and spaced 10 m apart, were taken at an elevation of 4100 m on the Bolshoy Azau glacier on the western slopes of Mount Elbrus. The cores were used for different physical and chemical analyses. Structure, texture and ice microstructure were studied. Chemical analyses of major ions (SO42−, NO3−, K+ and Na+) and measurements of insoluble light-absorbing material and radioactivity (137Cs and total β activity) were made. With the results of the physical and chemical analyses of these two ice cores, the possibilities of utilising the ice for the study of trace substances deposited after long-range transport from Europe were explored. Ice-stratigraphic methods made it possible to establish the annual accumulation rate. A reference horizon was established from the depth variation of 137Cs and total β activities that showed a well-defined peak of their activities coinciding in time with the 1986 Chernobyl accident. The results of this study show that Mount Elbrus is a useful archive for atmospheric composition downwind of Europe.
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

Fifteen 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

Borehole-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

The 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

Response 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

The 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

Tensile 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

The 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

Deep 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

Analyses 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

In 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

The 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

On 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

A 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

Statistical 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

The 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

A 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

This 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

A 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

A 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.
Annual Moraine Ridges at Skàlafellsjökull, South-East Iceland
Authors: Sharp Martin
Published: September 2017

Moraine ridges have formed annually at Skálafellsjökull, south-east Iceland since about A.D. 1912. These ridges are asymmetrical with a steeper distal slope, and their surface morphology reflects their internal structure. Most ridges are formed at the glacier margin, and they form a series of concentric arcs about it. Their plan form reflects small details of the ice-front morphology. Some ridges are composed of boulders released from the ice by ablation and swept together by glacier re-advances, but most have a core of deformed till. Those which were ice-cored have a surface veneer of resedimented debris consisting of ice-slope colluvium and sediment-flow deposits. Lodgement tills at Skálafellsjökull have a two-layer structure, with a weak upper horizon apparently formed by dilation during subglacial shearing of the till. Ridges are composed of this sheared material and overlie undisturbed lodgement till at depth. Subglacial shearing results in a discharge of till towards the glacier margin and its accumulation there when glacier retreat ceases in winter. Till may also be extruded from beneath ice at the margin as a result of loading by the ice, and subsequently bulldozed into a ridge by a winter readvance of the glacier.
Stable Isotope Analysis of a Submarine Ice Cliff at Explorers Cove, McMurdo Sound, Antarctica
Authors: Stockton William L. , DeLaca Ted E. , Deniro Michael J.
Published: September 2017

Stable isotope ratios and salinities of ice samples obtained from a submarine ice cliff at Explorers Cove demonstrate that the upper parts of the ice cliff have frozen directly from sea-water and are an underwater expression of permafrost, whereas the lower parts appear to be partially glacial in origin. These results indicate that there may be ice cores in the moraines of Explorers Cove, in which case the coastline of McMurdo Sound is more extensively ice-cored than previously known.
Mass Balance and Thermal Regime of Laika Ice Cap, Coburg Island, N.W.T., Canada
Authors: Blatter Heinz , Kappenberger Giovanni
Published: September 2017

During the North Water Project of the late F. Müller, glaciological studies were carried out on Laika ice cap. In addition to the main climatological investigations, surveying, mapping, mass-balance studies, and englacial temperature measurements were carried out. The mass-balance distribution is strongly determined by the orography. Strong westerly winds erode and transport snow from exposed surfaces, whereas prevailing easterly winds, during precipitation, deposit snow on lee slopes. The balance is negative under the present climate. The history of the glacier-tongue geometry is reconstructed using geomorphological observations and photogrammetric mapping for 1959 and 1971. Englacial temperature measurements revealed a finite layer of temperate basal ice in the ablation zone. The temperature distribution in the accumulation area around the summit of the ice cap is not stationary.
The Topography and Surface Characteristics of the Larsen Ice Shelf, Antarctica, Using Satellite Altimetry
Authors: Ridley Jeff , Cudlip Wyn , McIntyre Neil , Rapley Chris
Published: September 2017

A comprehensive survey of the Larsen Ice Shelf has been conducted using precise orbit and retracked Seasat radar-altimeter data with editing of erroneous values resulting from intrumental artefacts. Contour maps of elevation and radar back-scatter (with absolute accuracies of 1 m and 2 dB, respectively) have been produced and it has also been possible to map rifts, grounding points, rough terrain, and about 30% of the ice shelf’s seaward margin. Ice thicknesses derived from these elevation data show broad agreement with those derived from previous airborne radio-echo surveys. The maps of parameters measured by Seasat represent a very substantial improvement over those previously available. They thus provide a reference against which comparison may be made with a view to detecting substantial climatic changes. This is of particular interest since, as the most northerly major ice shelf in Antarctica, the Larsen Ice Shelf may be more sensitive than others to global climatic trends.
Time–Scale for Adjustment of Glaciers to Changes in Mass Balance
Authors: Jóhannesson Tómas , Raymond Charles , Waddington Ed
Published: September 2017

The length of time TMover which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models. We show the following: TMmay in general be estimated by a volume time-scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states. The factorfin the classical estimate of τM=ƒl/u, whereIis glacier length anduis terminus velocity, has a simple geometrical interpretation. Ft is the ratio of thickness change averaged over the full lengthIto the change at the terminus. Although bothuandfrelate to dynamic processes local to the terminus zone, the ratiof/uand, therefore, Tmare insensitive to details of the terminus dynamics, in contrast to conclusions derived from some simplified kinematic wave models. A more robust estimate of Tmindependent of terminus dynamics is given by TM=h/(–b)wherehis a thickness scale for the glacier and–bis the mass-balance rate (negative) at the terminus. We suggest that Tmfor mountain glaciers can be substantially less than the 1O2–103years commonly considered to be theoretically expected.
On the Development of Transverse Ridges on Rock Glaciers
Authors: Loewenherz Deborah S. , Lawrence Christopher J. , Weaver Richard L.
Published: September 2017

The stability of a low Reynolds number flow on an inclined plane is investigated with respect to modelling the initiation of transverse wave-like ridges which commonly occur on the surfaces of rock-glacier forms. In accordance with field observations indicating the presence of stratification in rock glaciers, two models of rock-glacier structure are considered, each stratified and possessing a lower layer which is treated as a Newtonian fluid. An upper, less compliant layer is treated, alternatively, as a Newtonian fluid of viscosity greater than that of the lower layer, or as an elastic solid under longitudinal compression induced by a decrease in the slope of the underlying incline. A linear stability analysis is used to examine the behaviour of each of the proposed models, and both are found to generate instabilities at wavelengths comparable to those associated with transverse surficial ridges on rock glaciers. The growth rates of a flow disturbance predicted by the viscous-stratified model appear to be too slow to account fully for the development of wave forms of finite amplitude, suggesting that other mechanisms are involved in the amplification of an initial disturbance. The results of the stability analysis of the elastic lamina model indicate that finite surficial ridges may develop on rock glaciers as a product of a buckling instability in the surface region if there is a decrease in the slope of the underlying incline. Both of the analyses illustrate that transverse ridges can occur on the surface of a rock glacier in the absence of any variations in debris supply to the system. The results further imply that the use of these features in the paleoreconstruction of Holocene climatic conditions must entail an assessment of the relative roles of external climatically driven forcing versus internal Theologically derived instability.
Airborne UHF Radio Echo-Sounding of Three Yukon Glaciers
Authors: Narod B. B , Clarke G. K. C.
Published: September 2017

A high-resolution radio echo-sounder operating at a frequency of 840 MHz has been developed for airborne sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact,, high-gain antenna which suppresses valley-wall echoes and simplifies operation from light aircraft, Successful field trials were carried out on Rusty, Trapridge, and Hazard Glaciers, Yukon Territory, Canada. Results compare well with ice depths obtained from earlier ground-based soundings on Rusty and Trapridge Glaciers. The maximum ice thickness encountered was 200 m on Hazard Glacier.

Owing to the high operating frequency, random scattering from inhomogeneities within the ice is a major cause of signal degradation. For this reason the sounder cannot penetrate great thicknesses of temperate or debris-rich ice. Spatial averaging, an immediate result of operating from a moving platform, reduces the effects of back-scattered “clutter”.
Nivation: An Arctic-Alpine Comparison and Reappraisal
Authors: Thorn Colin E. , Hall Kevin
Published: September 2017

Nivation is a collective noun identifying a set of geomorphic processes, comprised of an indeterminate number of elements and of unknown relative importance, for which there is little likelihood of ever producing a precise definition. Instead, attention should first be directed towards the relationships between snow-packs and individual geomorphic processes. The relationship between freezing amplitude in the bedrock, snow cover, and aspect at an Arctic site in northern Norway and an alpine site in the Front Range, Colorado, U.S.A. is complex. Comparison of field data and laboratory criteria permit several conflicting interpretations. If oscillations across 0°C, regardless of freezing amplitude, are critical, the alpine site is potentially a more active freeze-thaw weathering regime, with a primary springtime peak and a secondary fall peak. If a freezing amplitude of –5°C is required for effective freeze-thaw weathering then the alpine site is largely inactive and the Arctic active (but with only a single fall peak). Chemical weathering is much more important at snow-patch sites than has traditionally been recognized. Mass wasting at colluvial sites subject to snow patches is dominated by interaction between overland flow and solifluction when the site is unvegetated, and by solifluction when it is vegetated. Given contemporary knowledge of snow and glacial geomorphology, there appears to be no threshold, only differences of intensity. Resolution of the disruptive mechanism associated with bedrock freezing and its constraining temperature and moisture requirements is the most pressing present problem in the field of snow geomorphology.
Does the Permanent Creep-Rate of Polycrystalline Ice Increase with Crystal Size?
Authors: Duval Paul , Gac Hugues Le
Published: September 2017

Uniaxial compression creep tests were performed on artificial and natural polycrystalline ices at temperatures near –7°C. The grain-size range investigated was from 1 to 10 mm. Contrary to previous results, the permanent creep-rate was not found to increase with crystal size. Only the transient creep appears to be sensitive to variations in crystal size.
Elastic Constants of Ice by Brillouin Spectroscopy
Authors: Gammon P. H. , Kiefte H. , Clouter M. J.
Published: September 2017

Brillouin spectroscopy has been used to measure the adiabatic elastic constants of laboratory-grown pure monocrystalline ice Ih at – 3°C. The values obtained were (in units of 108 N/m2): c11 = 136.96 ±0.60, c12 = 69.66± 0.45, c13 = 56.28±0.31, c33 = 147.02±0.68, c44 = 29.59±0.15. Comparison of these values with ultrasonic measurements quoted in the literature reveals no significant acoustic dispersion in ice over frequencies ranging to 1010 Hz. However, the results suggest that the elastic constants of ice may depend on the precise crystal quality and age of a given sample. The low experimental error in the values obtained, along with the inherent versatility of the method, indicate that Brillouin spectroscopy is an effective technique for systematically investigating the elastic properties of ice samples formed under natural conditions.
A Fast Light-Weight Core Drill
Authors: Johnsen S. J. , Dansgaard W. , Gundestrup N. , Hansen S. B. , Nielsen J. O. , Reeh N.
Published: September 2017

A core drill capable of drilling to more than 100 m depth in cold ice is described. It is designed with a view to fast operation and easy transport, core handling, and maintenance.
The University Course in Snow Dynamics —A Stepping-Stone to Career Interests in Avalanche Hazards
Authors: Montagne John
Published: September 2017

The principles of snow dynamics, including practical field work, constitute a feasible university-level course where seasonal snowfall and terrane of varying steepness are accessible. Two to three lectures or discussions per week are combined with one full afternoon in the field to provide a workable course format. We have successfully used the U.S. Department of Agriculture Forest Service Agriculture Handbook 489 (Avalanche handbook) as a text but also assign readings in diverse world literature.

Field work has centered on standard techniques for snow study in a realistic alpine setting but could easily be adapted to more simple “roadside” conditions if necessary. Student interest during and following the course usually leads to spontaneous and practical research that tends to develop life-long skill and application in the subject.

Our experience indicates that one instructor can manage a maximum of 25 students in the field, considering proper logistics, safety, and necessary adaptibility of field procedures to changing weather conditions.
Snow Stratigraphy and Water Equivalence Measured With an Active Microwave System
Authors: Ellerbruch D. A. , Boyne H. S.
Published: September 2017

This paper reports on research on the relationship between the electromagnetic scattering properties and physical properties of snow-pack. An FM-CW active microwave radar system operating in the frequency range 8-12 GHz is used to scatter electromagnetic radiation from surface and subsurface stratigraphic layers in the snow-pack. The amplitude of the scattered radiation as a function of depth in the snow-pack can be correlated with such physical characteristics as density, hardness, stratigraphy, and moisture content. A direct determination of snow-pack water equivalence can be made from these observations.
Propagation of Stress Waves in Alpine Snow
Authors: Brown R. L.
Published: September 2017

The propagation of pressure waves in low-density snow is investigated analytically to determine the variation of wave pressure and wave speed with density and frequency. The results show that, for pressure waves that produce finite volumetric deformations, both pressure jump across the wave and wave-speed increase with initial density and final density. The pressure jump was also found to increase with the wave frequency if other parameters were held constant, although the dependence on frequency is not as strong as the dependence on the initial and final densities. The relationship between pressure jump and frequency implies that high-frequency waves would tend to dissipate more quickly than lower-frequency waves, although like pressure, the attenuation rate would not be strongly frequency dependent.
Tensile strain and fracture of snow
Authors: Watanabe Zempachi
Published: September 2017

Measurements over several hours of the tensile strain of snow have been carried out, and the strain-rate e can be expressed in terms of stress σ, elapsed time t, and (Celsius) snow temperature T as . It is evident from this expression that a creep fracture does not happen without either an increase of stress or a rise of temperature. We observed the phenomenon of creep fracture of snow by these two methods.
History and Actual State of Legalization of Avalanche Zoning in Switzerland
Authors: Frutiger Hans
Published: September 2017

Tourism in the Swiss Alpine region has developed rapidly in the last 20 years. Many new routes transport systems, and tourist resorts have appeared for which the planning and construction have inadequately considered the avalanche danger. The local authorities are responsible for the safety and welfare of the inhabitants and visitors. This is especially true with respect to land-use control and the issue of building permits. Since property values have risen considerably since the second World War, speculation in land that is not safe from hazard has become widespread. This speculation has led to numerous conflicts between property owners and the municipal government as well as between sellers and buyers of land which is later found to have an avalanche hazard. In Swiss law a legal basis is required to prohibit building in unsafe places. This basis did not exist in many Swiss cantons when these fateful developments began. This study will show how the legal basis for avalanche zoning has been developed at the federal, cantonal and communal levels and what the actual state of jurisdiction is. Of special interest are the “precedents” or “case law” which are presented and discussed in this paper. It also gives definitions of the terms “zone”, “avalanche zoning”, “avalanche hazard map”, and “avalanche zone plan”.