bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments on Ice Ride-Up and Pile-Up
Authors: Sodhi D. S. , Hirayama K. , Haynes F. D. , Kato K.
Published: September 2017

Ice pile-up and ride-up are common occurrences along beaches in the sub-Arctic and Arctic. An understanding of the factors which lead to pile-up is important for design of a defensive strategy to prevent damage to coastal installations.

Since ice action on a sloping beach is complex, an experimental model study was undertaken to determine the factors which promote ice pile-up. The factors varied in this study were the freeboard, slope, and roughness of the beach. One experiment was performed to observe the effectiveness of a shore defense structure against ice ride-up.
Numerical Modelling of Realistic Ice Floes in Ocean Waves
Authors: Squire Vernon A.
Published: September 2017

Results from a numerical model for the computation of ice-floe motions in ocean waves are presented and discussed for floes of various sectional shapes. It is shown that the beam-to-draft ratio is a crucial factor in determining the behaviour of each floe, and that ridges and keels can substantially affect the roll and sway characteristics, particularly for thick floes. Undercuts beneath floes appear to have little effect, but a protruding sill can lead to decreased motion at certain frequencies and a reduced capability for making waves. As the underwater character of an ice floe cannot easily be measured, it is necessary to infer draft from freeboard estimates using the method proposed by Ackley and others (1976). Although most of this paper is concerned with rigid body motions, a brief account is included of a modification to the model which allows each floe to bend on the passing wave. By this means, wave-induced flexure is discussed for floes of non-simple underwater shape.
Measuring Snow Water Equivalent by Cosmic Radiation
Authors: Fritzsche W.
Published: September 2017

We have reduced the time taken for measurement of snow water equivalent using cosmic radiation by two to four hours with an accuracy of 1 cm of water equivalent. When BF3 counters were used by Kodama in 1975, it took three days. For comparison we sometimes still have to make measurements manually or automatically in flat areas. These measurements can then be compared with measurements from avalanche starting zones where conditions can be quite different because of wind or ablation.

For avalanche forecasting, or in similar situations, when an accuracy of 1 cm is needed within a few hours, we suggest the use of scintillation counters with a doped plastic material. The greatest accuracy is obtained by using a separate site where values are recorded without snow. In this case 200 000 pulses per hour are obtained (absorption length of 400 cm) which after measurements of 2 h duration gives the desired error of 1 cm of water. After 8 h the error is 0.5 cm of water, and after 24 h it is 0.3 cm of water. At an altitude of 2 000 m at which most avalanches are released, the count rate is doubled and the measuring error is 0.7 of that at sea-level. At an altitude of 3 000 m the count rate is four times that at sea-level. In other regions at other latitudes and elevations other values would be found.

The necessary equipment can be built into the ground in autumn so that the surface is level with the ground. A slot antenna of frequency around 400 MHz is used for transmission of the data.
Implications of the Time Required for Minimum and Tertiary Creep Rates for Ice Mining and Tunnel Closure (Abstract only)
Authors: Jacka T. H. , Budd W. F.
Published: September 2017

For the calculation of rates of closure of tunnels or bore holes in ice, the use of a flow law relation based on secondary or minimum creep rates necessarily underestimates closure rates, particularly for large strains where much higher tertiary creep rates develop. Long-term laboratory studies have shown that the change in strain-rate from primary to secondary or minimum and to an approximately constant tertiary stage is associated with recrystallization and the development of strong crystal-orientation fabrics which are dependent on the stress configuration, but not appreciably on crystal size. For bore holes, tunnels or cavities constructed in ice, initial rates of closure decrease, in primary creep, to a minimum value (at about 1% strain) dependent on stress and temperature. From this time, increasing strain-rates occur, analogous to the results obtained from the laboratory studies.

A 25-year record of closure of a tunnel at about 30 in depth at site S2 on Law Dome, Antarctica, illustrates the application of the laboratory-derived relations. Comparison between the results of deformation from bore holes, tunnels and laboratory tests, comprising various stress configurations, under similar conditions of stress and temperature, indicates that the strain-rates are compatible when considered as a function of total strain.
Preventing a Collapse of the West Antarctic Ice Sheet: Civil Engineering on a Continental Scale (Abstract only)
Authors: MacAyeal D. R.
Published: September 2017

A collapse of the West Antarctic ice sheet due to warming by atmospheric carbon dioxide is a potential threat to mankind because low-lying land would be flooded by rising sea-level. Intervention would be possible by creating one or several artifical ice rises on the floating ice shelves surrounding the West Antarctic ice sheet. Ice rises are places where the ice shelf has run aground locally on the sea bed. Existing ice rises obstruct ice flow and are responsible for maintaining the ice sheet in its present stable condition. An artificial ice rise could be created by (1) drilling a hole through the ice shelf in a choice position such as over a sea-bed ridge, (2) pumping large volumes of sea-water from beneath the ice shelf so as to flood the surface, and (3) continuing to pump until the frozen sea-water has thickened the ice shelf by 100 m over an area of 100 km2. Approximately 1.6 × 106 kW of power would be required to accomplish the task in ten years. This would cost approximately 20 × 109 US dollars.
Modelling of Ice Accretion on Wires (Abstract only)
Authors: Makkonen Lasse
Published: September 2017

A time-dependent numerical model of ice accretion is used to simúlate the growth of ice loads on wires. Both dry growth (rime) and wet growth (glaze) are modelled in order to examine the dependence of the growth rate of ice load on atmospheric conditions.

The results show that during dry growth under constant atmospheric conditions the growth rate of an ice load slightly decreases. In conditions of wet growth, however, the growth rate increases until the process turns to dry growth after reaching the critical deposit diameter. The effect of air temperature on the growth rate in dry growth turns out to be rather small. However, the final ice load after long-term rime formation is temperature-dependent, because the limiting deposit diameter, at which the collection efficiency becomes practically zero, is reached at different ice masses depending on the ice density.

The modelled relationships between the growth rate of ice load and the atmospheric variables are compared with observational data and with proposed formulae for the calculation of the intensity of wire icing. The possibilities of estimating the formation of ice loads for practical purposes with a simple method, using the routinely measured meteorological parameters only, are discussed.
A Contribution to Avalanche Dynamics: A Formal and an Exact Solution of the Voellmy/Perla Two-Parametric Equation of Motion (Abstract only)
Authors: Schieldrop Bonsak
Published: September 2017

The two-parameter equation of motion for snow avalanches proposed by Voellmy in 1955 was later formally derived by Perla in 1979. It has been the object of numerous investigations, mainly to its applications. It has been solved for tracks approximated by straight lines, and this solution has, in some countries, been used extensively with a two-segment approximation. Perla and Cheng programmed such a solution for digital computation by matching an arbitrary number of straight line segments. This solution can also include impact losses due to abrupt changes in the track.

In the first part of this paper a formal integration of the Voellmy/Perla equation is carried out for the general case of a track. The averaged values of the different terms are discussed and evaluated as to their relative orders of magnitude. It is shown that the “centrifugal” effect, which is, of course, automatically omitted in the straight-line solution, can be neglected in most cases. As a conclusion it is shown that all avalanche motions governed by the Voellmy/Perla equation will have the same average velocity on all tracks having the same vertical drop H, the same horizontal extension L, and the same set of “friction” parameters, as long as the length S of the track is the same, regardless of the shape of the tracks. The shape will only determine the velocity profile along the track.

The second part of the paper shows the exact solution of the equation for the special case of tracks with constant curvature, i.e. circular arcs. If the conclusion of the first part of the paper holds true, this solution can be used to determine the average velocity on other shaped tracks of the same length, etc.

It is finally shown that a number of well-known avalanches described in the literature can well be approximated by a circular arc. In these cases even the velocity profile is determined by the exact solution.
Vertical Lifting Ice Forces Caused by a Rising Water Level, and their Action on a Vertical Slender Structure (PILE) (Abstract only)
Authors: Tryde Per
Published: September 2017

The problem of vertical lifting ice forces caused by a rising water level, and their action on a vertical slender structure (pile), has been studied by use of the classical theory of an elastic plate resting on an elastic support, in order to calculate the moments and normal forces in the sheet that cause rupture and thus produce cracks in the sheet (Nevel 1974). When cracks are formed, the continuous rise of the water level tends to widen them further, and the theory of elasticity is no longer valid. Usually, formation of cracks in structural members results in complete failure, but this may not be the case here. If the temperature of the air is below zero, the water penetrating the cracks will freeze when it meets with the upper part of the ice and with the air, both having a temperature far below the freezing point of water. Thus the cracks will be continuously healed up, as they are widened by the rising water level. A material healing its own cracks along the rupture zone gives a completely changed stress/strain situation during the deformation.

This new approach may lead to a theory which is able to predict the uplift forces of ice as a function of time, of frequency and amplitude of water-level fluctuations, and of air temperature. It appears that the pile is lifted only a short distance with each cycle of water-level fluctuation. Since the downward ice force is smaller than the upward force, and the pile has a larger resistance to compression than to pulling, the pile may eventually, in the course of repeated cycles, be lifted several metres.
The Institute for Snow and Avalanche Research at Weissfluhjoch/Davos: The First Five Years (1943 to 1948)
Authors: Quervain Marcel R. de
Published: September 2017

This essay is not a scientific paper in the usual sense; it is rather a personal retrospective view, presented as an oral account of a period of snow research spent almost in isolation. For this printed version a few adaptations have been made, including a reduction in the number of figures. Original illustrations from the Interval Reports of the Institute of Snow and Avalanche Research were used to illustrate the talk and have been retained for publication. Although some information is in German, the essential content of the figures is repeated in English in the captions.
Spatial and Temporal Variations of Snow Chemistry in Terre Adélie (East Antarctica)
Authors: Legrand Michel , Delmas Robert J.
Published: September 2017

The chemistry of recently deposited snow sampled in 1982–83 along a 430 km coast-interior traverse in Terre Adelie, East Antarctica, is reported. In addition, three firn samples, covering the same time period (1959 to 1969) and collected on the traverse at D 55, D 80 and Dome C stations, respectively at 200, 430 and 1070 km from the sea, are also studied. Concentrations of major soluble impurities (H+, , Na+, K+, Cl−, and ) were determined by ion chromatography (except H+ which was titrated) on more than 200 samples. Conditions of sampling and analysis were carefully controlled in order to avoid contamination problems. A balanced ionic budget was generally obtained for each of the samples. For stations occupying an intermediary position between the coastal areas and the central Antarctic plateau, our results demonstrate that the two major impurities are H2SO4 and HNO3. HCl is also present, but at a lower level of concentration; the sea-salt contribution is dominant only at the most coastal sites (within 40 km) of the sea. The degree of neutralization of the snow acidity by NH3 is always very low as indicated by the values of content. The mean concentrations of H2SO4 along the traverse are relatively constant whereas an increase of the HNO3 concentrations is observed when going inland. It decreases, however, in most central areas. These results are discussed in relation to the glaciochemical data published for other locations on the Antarctic plateau, in particular the sulphate concentrations which depend strongly on explosive volcanic activity.
The Influence On Atmospheric Composition of Volcanic Eruptions as Derived From Ice-Core Analysis
Authors: Hammer C.U.
Published: September 2017

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.
The Roles of Snow, Lake Ice and Lake Water in the Distribution of Major Ions in the Ice Cover of a Lake
Authors: Adams W.P. , Lasenby D.C.
Published: September 2017

The stratigraphic variability of ion concentration in lake ice was examined and related to the processes of lake-ice formation. Ice blocks obtained from Elizabeth Lake, Labrador and Knob Lake, Quebec showed marked vertical variation in the concentration of major ions, with peaks in conductivity occurring in the white ice and an overall increase in conductivity upwards from the black-ice/white-ice interface to the top of the block. Exsolution of ions from the black ice into the water body appears to be very efficient, producing low concentrations of ions in the black ice and high concentrations in the immediate sub-ice layer of water. This sub-ice concentration of ions appears to influence the entire water column, possibly via density-induced movements. Changes in snow depth, white- and black-ice growth, and the vertical distribution of conductivity in the water column were found to be related to slushing events. A controlled slushing experiment suggested that a marked concentration of ions does occur during white-ice formation.
Effects of Ice and Snow Cover on the Chemistry of Nearshore Lake Water During Spring Melt
Authors: Gunn J.M. , Keller W.
Published: September 2017

Snow and ice played important roles in determining the occurrence and timing of pH depressions in the shallow (∼1 m) nearshore waters of a small lake of the Canadian Shield. The influences of the terrestrial snowpack and lake-surface snow on the chemical composition of under-ice water were distinctly different. On land, acidic meltwater from snow was enriched with lithological elements in the soil/litter layer during lateral movement to the lake shoreline. The resulting run-off water was of relatively high ionic strength (X conductivity 55 μS cm−1), low pH (X 4.1) and contained high concentrations of Al (X 1786 μg 1−1), an element potentially toxic to aquatic biota. Snow cover on the ice surface controlled thermal conditions in the underlying water, dictating the depth to which run-off water penetrated. Uniformly cold conditions (<2°C) allowed penetration of run-off water to the substrate while under-ice warming to 4°C resulted in surface layering of less dense run-off water. flooding of the ice with lake water and melting of the ice and snow-surface cover served to counteract the effects of the run-off water through dilution.
Comparison of Results From Transit Satellite Tracking
Authors: McDonald James , Whillans Ian M.
Published: September 2017

Large-scale motions and strain-rates over great distances on polar ice sheets are often obtained from the tracking of Transit (or doppler) satellites. The results of different processing techniques for these tracking data are compared, using some of the data collected on and near Ice Stream C. Reduction is made by using the software packages CALIPER, GEODOP V, MAGNET, and the micro-processor on the Magnavox MX 1502 satellite receiver. The orbital data broadcast by the satellites are used, as well as more precise orbits obtained afterward. In addition, calculations are made for single sites individually (point positioning) and for many sites with simultaneous tracking data (network adjustment).

The results agree within the range of known errors associated with the orbits. Earth-based positions (latitude, longitude, ellipsoidal height), based on the broadcast orbits, agree to within 41.1 m. Positions with more precise orbits are within 0.7 m of one another. Relative positions are best obtained by using network techniques, and these agree with terrestrial survey results within 0.2 m in horizontal separation for sites 19 km apart, and are within 4.8 m in elevation difference. The calculated azimuth differs by 1.5 m/19 km or 10−4 rad.
Closure Rate of a 700 m Deep Bore Hole at Mizuho Station, East Antarctica
Authors: Naruse Renji , Okuhira Fumio , Ohmae Hirokazu , Kawada Kunio , Nakawo Masayoshi
Published: September 2017

Measurements of the bore-hole diameter were made with three-contact-point calipers from the shallow layer to a depth of 700 m at Mizuho Station, East Antarctica, in 1984–86. The minimum strain-rate (i.e. secondary creep rate) of the bore-hole closure was estimated from the observed creep curve at each depth. A relation between stress and strain-rate was deduced for a temperature of −35°C and a stress range from 0.8 to 1.65 MN m−2, as

where is the effective strain-rate (s−1) and τ is the effective shear stress (MN m−2). This result shows that, for comparable overburden stresses and temperature, the bore-hole closure rates at Mizuho Station are higher than those measured in bore holes at Byrd Station and in the Northern Hemisphere ice caps (Paterson 1977).
Special Aspects of the Central Part of Filchner-Ronne Ice Shelf, Antarctica
Authors: Thyssen F.
Published: September 2017

Aero-measurements during the 1983–84 and 1985–86 field seasons showed that the ice in the central part of Filchner-Ronne Ice Shelf is more than 250 m thicker than has been assumed previously. In the margin area a double layering of the ice was found, with disappearing bottom reflections farther inland. High absorption of approximately 0.3 dB/m in the lower layer and a decreasing reflectivity at the ice / sea-water interface, probably caused by bottom freezing, have been estimated. Aero-measurements were used to map the surface elevation of the ice, with an accuracy of approximately 3 m. From the plot of ice thickness against surface elevation it was possible to obtain a calibration curve for isostatic conditions. Large deviations from this plot with an ice thickness which is apparently too small (they seem to be isostatic anomalies) were found in the central part of the ice shelf. The true ice thickness could easily be calculated and mapped from these anomalies and the electromagnetically measured thickness.

From the map based on flights made in 1983–84 the site for a bore hole was chosen in the central part of the ice shelf with an estimated ice thickness of about 450 m, instead of the less than 200 m deduced by an electromagnetic reflection (EMR) method. Hot-water drilling by the ground party of our group (H. Engelhardt and J. Determann) revealed an ice thickness of 465 m at this site.
A Pulse-Counting Technique for the Measurement of Drifting Snow
Authors: Tüg H.
Published: September 2017

For the study of drifting snow a pulse-counting device was developed. The detector is sensitive to the momentum transfer of individual snow particles to an exposed surface. More than 105 particles can be counted per cm2/s. The sensor is adjusted to snow particles of 30–200 μm in diameter and a velocity range of 5–30 m/s. A multi-channel analyzer system is used for data handling and to display the momentum spectrum in real time.
Density-Depth Profile Determined by Seismic-Refraction Studies: Ice Stream B. West Antarctica (Abstract)
Authors: Anandakrishnan S. , Blankenship D. D. , Alley R. B. , Bentley C. R.
Published: September 2017

Detailed seismic short-refraction profiling was conducted on Ice Stream Β (UpB) during the 1983–84 austral summer. A new high-resolution data logger, developed at the University of Wisconsin, recorded both compressional- and shear-wave arrivals. We report here on P-wave and S-wave profiles recorded along a line parallel to the axis of the ice stream. Source-receiver separations up to 720 m yielded seismic velocity-depth curves to below the firn-ice transition zone (slightly greater than 30 m at UpB).

For the compressional-wave profile, geophones were separated by 2.5 m, which yielded a velocity-depth curve with a granularity of ∼1 m. The corresponding density-depth curve agrees well with direct density measurements obtained from a core extracted nearby (Alley and Bentley 1988, this volume). Discontinuities in the velocity gradient do not appear at the “critical densities” as they did at Byrd Station, Antarctica, and elsewhere (Kohnen and Bentley 1973, Robertson and Bentley 1975).

Two shear-wave profiles were recorded, both with geophone spacings of 5 m, one with longitudinal polarization (SV) and the other with transverse polarization (SH). There is a marked difference in velocity between the SH and SV waves, particularly in the shallow firn. We suggest that a strong vertical shape-and-bonding fabric in the shallow firn, as observed in cores collected at UpB, would account for this disparity.
Seismic Measurement of the Gross Crystalline Structure of a West Antarctic Ice Stream (Abstract)
Authors: Blankenship D. D. , Bentley C. R.
Published: September 2017

Both in the interior of West Antarctica and on Ross Ice Shelf the ice column is dominated by ice with a distinct preferred c-axis orientation. An understanding of the dynamics of the West Antarctic ice sheet requires that we know the gross crystalline structure that characterizes each of its glaciological regimes (i.e. ice sheet, ice stream, and ice shelf). An important question is whether the strong fabric of the interior ice is preserved when this ice passes through the zone in which it is accelerated from sheet flow to stream flow, a zone that must be marked by strong longitudinal extension. Using generalized inverse techniques we have inverted seismic-reflection travel times observed at Upstream Β camp (on Ice Stream B) to obtain the gross crystalline structure of the ice column at that location. We find that the strong fabrics of the interior are indeed destroyed; only a slight preferred orientation remains. The evidence at Upstream Β camp is particularly strong because shear waves of both polarizations, which are particularly sensitive indicators of anisotropy, were analyzed as well as P-waves.
Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)
Authors: Dahe Qin , Young N. W.
Published: September 2017

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1.

The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed.

The following observations were made and conclusions reached:

1.

Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher.

2.

The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature.

3.

The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature.

4.

The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet.

5.

At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.
Force Budget (Abstract)
Authors: Whillans I. M. , van der Veen C. J.
Published: September 2017

An expression for force balance is derived for the general case of gradients in longitudinal and lateral normal stresses and lateral shear stress. In order to consider horizontal glacial mechanics in Newton’s style of actions and reactions, the full stresses are partitioned into lithostatic and resistive, Rij, components. The lithostatic stress is the weight of ice above, and the horizontal gradient in lithostatic force on a vertical column is the familiar driving stress, which accounts for the horizontal effect of body or action forces. The horizontal resistive-stress components describe the reactions to this horizontal action of gravity. Force balance is

with horizontal coordinates x1, x2 and vertical z. The upper and bottom elevations are h and b, and τdi and τbi are driving stress and basal drag respectively. This describes net reaction due to normal resistance, lateral shear resistance, and basal drag resistance, and finally the action or driving stress. This equation is exact. Resistive stresses are simply linked to deviatoric stresses, and hence to strain-rates, through the flow law.
Force Budget: Application to Three-Dimensional Flow of Byrd Glacier, Antarctica (Abstract)
Authors: Whillans I. M. , Chen Y. H. , van der Veen C. J. , Hughes T. J.
Published: September 2017

Stresses at the surface and at depth are calculated for a stretch of Byrd Glacier, Antarctica. The calculations are based on photogrammetrically determined velocities and elevations (Brecher 1986) and on radio-echo-determined ice thicknesses. The results take the form of maps of drags from each valley wall, of normal forces laterally and longitudinally, and of basal drag. Special challenges in the calculation are the numerical gridding of velocity (ensuring that unreasonable short-wavelength features do not develop in the calculation) and inference of ice thicknesses where there are no data.

The results show important variations in basal drag. For the floating part, basal drag is near zero, as expected. Within the grounded part, longitudinal components of basal drag are very variable, reaching 300 kPa, with a dominant wavelength of 10 km. Generally these drag maxima correlate with maxima in driving stress, and the across-glacier component of basal drag is usually small. An important exception occurs in the center of the grounded part of the glacier, where the flow shows major deviations from the axis of the valley.

Results also show that side drag is roughly constant at 250 kPa along both margins of the glacier, tension from the ice shelf is about 100 kPa, and tension in the grounded part cycles between 250 and 150kPa. Calculated deep velocities are too large and this is attributed to deficiencies in the conventional isotropic flow law used.
Development of the Crystal Structure within the Law Dome Ice Cap, Antarctica (Abstract)
Authors: Young Neal W.
Published: September 2017

Fourteen shallow and medium-depth cores have been drilled from the Law Dome ice cap, between the summit and the coast near Casey Station. Measurements of their crystal and other physical properties are reviewed briefly. The variations along the cores in crystal size, orientation, fabric type and strength, and bubble dimensions, are used to define the internal structure of the ice cap locally at the bore-hole sites. Surveys of bore-hole deformation and the shape and movement of the ice cap are used to define relations between the structure and the variables: stress, temperature, strain-rate and accumulated strain. The relations and the survey data are incorporated in a numerical model in order to deduce the internal structure of the ice cap along a flow line linking the bore-hole sites. The results of the model in turn depend on the crystal anisotropy of the calculated structure.

The main results are provided by the medium-depth bore holes located at the summit, near the margin, and about half-way along the flow line. The major features of the internal structure are determined by the predominant shear deformation in the ice cap. There is horizontal continuity in the properties and structure within the group of bore holes near the margin of the ice cap. There are distinct differences, between the coastal and the inland ice cores, in the changes in properties with depth. Near the margin a strong single-maximum fabric develops within the upper 60% of the ice thickness; crystal size initially increases with depth, then shows a marked decrease at about 50% thickness. For the inland cores, a strong single-maximum fabric also develops, but at a greater total depth and a much shallower fraction of the thickness. A similar decrease in crystal size was not observed.

The broad-scale trends of the properties are reproduced by the model. The finer-scale deviations in the properties can be explained by the effects of longitudinal strain and of past changes in surface conditions, such as the effect of surface melting. A complex stress distribution, related to flow over rough bedrock, needs to be invoked to explain the pronounced multi-layer structure in the lower part of the ice cores from near the margin. A series of time lines is modelled, following the flow along the ice-particle trajectories, to produce the stress, temperature and deformation histories of the ice in the cores. These provide the basic data for a reconstruction of past changes in the ice cap.
Two-Dimensional Thermo-Mechanical Modelling of Flow and Depth-Age Profiles Near the Ice Divide in Central Greenland
Authors: Dahl-Jensen Dorthe
Published: September 2017

The ice divide on an ice sheet is a special place on the ice sheet, where the velocity and stress distributions are different from those found just two ice thicknesses from the ice divide. A two-dimensional thermo-mechanical model has been used to model the flow near the ice divide in central Greenland. The results show that the surface strain-rates are increased by 50% of the values found 15 km down-stream and that the basal temperatures rise by 3°C. Estimates of a depth–age distribution in the vicinity of Crête show that the isochrones rise at the dome. The model calculations predict 1600 m of Holocene ice, 1000 m of Wisconsin ice, and 400 m of ice older than 115kyear. 15 km down-stream from the dome, the thickness of ice older than 115 kyear will be reduced by 50%. In these calculations it has been assumed that the ice thickness at the dome is time-invariant. The existence of the old ice depends on the basal temperature. The estimates of the basal temperature depend strongly on past accumulation rates and on the geothermal heat flux but the ice has most likely been below the pressure-melting point throughout the last glacial period.
Some Dynamics Studies on Urumqi Glacier No. 1, Tianshan Glaciological Station. China
Authors: Maohuan Huang , Zhongxiang Wang , Baolin Cai , Jiankang Han
Published: September 2017

The zero isopleth of surface areal strain-rate is roughly parallel to, but below, the equilibrium line of the glacier. In the middle and lower parts of the ablation area, the basal temperature is either close to or at the melting point, whereas above and around the equilibrium line the glacier is frozen to its bed. The basal bulk ice is deforming continuously and inhomogeneously but, in the inner parts of the glacier, where the strain-rate is smaller, homogeneous deformation can only be assumed conditionally. In the ablation area, pure shear is predominant near the base of the glacier and simple shear becomes progressively more important from the inner parts of the glacier towards its margins.
On the Underside Scarring of Floating Ice Sheets
Authors: Musil G.J.
Published: September 2017

Detailed analysis of radar images, obtained using a synthetic aperture radar technique, from the bottom surface of a floating ice sheet suggests the presence of linear, groove-type scarring. The dominant physical parameters, such as the orientation, depth, and periodicity of the underside scarring, are derived. Although these results relate to the bottom roughness of Bach Ice Shelf (Alexander Island), Antarctica, close to its line of grounding, they are comparable to those of the underside of Ross Ice Shelf. It therefore seems probable that the roughness parameters, measured on Ross Ice Shelf using standard radio-echo techniques, relate to linear grooves which were introduced in the region of ice grounding. Such scarring runs along the direction of ice flow and is thought to be a drawn-out imprint of the bedrock surface where the ice was last grounded.
Interpretation of the Temperature Profile Measured at Vostok, East Antarctica
Authors: Ritz Catherine
Published: September 2017

The temperature profile measured in the Vostok bore hole is analysed. The temperature distribution in polar ice sheets depends mainly on past surface temperature, geothermal flux, and accumulation rate. In the present work, the heat equation is solved both for ice and for the underlying bedrock. The Vostok ice core offers a 160 000 year climatic record which is used to define the past surface temperature, while accumulation-rate variations are assumed to be governed by the saturation vapour pressure. The model is run for a number of different sets of parameters in order to find the parameter associations giving a good fit between the observed and the computed temperature profiles. With this model, it is possible to simulate the measured temperature profile within 0.1°C. To obtain this good fit, geothermal flux has to be higher than 50 mW/m2 and present-day accumulation rate must be lower than 2.6 cm/year. Sensitivity of these results both to the amplitude of surface-temperature change and to the velocity profile with depth is also investigated. Finally, it is shown that ice is at the melting point at the base of the ice sheet, which is in agreement with the presence of a subglacial lake near Vostok Station.
Super-Critical Reflection of Ocean Waves; A New Factor in Ice-Edge Dynamics?
Authors: Squire Vernon A.
Published: September 2017

Movement of the sea-ice edge on short time-scales (<1 d) is due to a balance of forces between several mechanisms (wind stress, sea-surface tilt, internal ice stress, and Coriolis force) which are often comparable in magnitude. Other factors such as the force induced by partial reflection of short seas, internal gravity waves in the pycnocline, etc., may also contribute. Through the momentum equation, these mechanisms affect the dynamics of the ice edge. In this paper we suggest another mechanism which may have importance, namely, a radiation-stress contribution which derives from obliquely incident waves which are totally reflected from the ice edge by a process analogous to total internal reflection in optics. Such reflection generates both normal and shear forces at the ice edge, the former tending to compact the pack ice and the latter to shear the absolute edge. The effect is studied using some recent data collected during the Winter Weddell Sea Project 1986 in Antarctica, where it is found that the contribution to the force balance is significant. For thicker sea ice and icebergs acted upon by oblique seas, the radiation stress-induced force may outweigh more conventional terms in the momentum equation.
Computational Ice-Divide Analysis of a Cold Plane Ice Sheet Under Steady Conditions
Authors: Szidarovszky F. , Hutter K. , Yakowitz S.
Published: September 2017

The dimensionless form of the field equations and boundary conditions governing plane flow of a grounded cold ice sheet emerge from balance statements of mass, momentum, and energy. They constitute an amended version of a reduced model of ice-sheet flow, due to Morland (1984) and Hutter (1983), and circumvent the restrictions imposed by the reduced model, namely the neglect of the longitudinal stretching effects. The amended version permits satisfaction of mass balance at the ice divide for arbitrary basal sliding conditions and gives a better reproduction of the local flow features.

Under very mild simplifying assumptions, namely that horizontal thermal conduction can be ignored close to the divide, we present a numerical analysis of the ice divide which has second-order accuracy. This analysis permits determination of the temperature profile, velocity, and stress distributions in a symmetric ice divide, provided that the ice-divide height, the local behavior of the accumulation and surface-temperature functions, and the geothermal heat flow are prescribed.
Small-Amplitude, Short-Period Variations in the Speed of a Tide-Water Glacier in South-Central Alaska, U.S.A.
Authors: WaIters Roy A.
Published: September 2017

An analysis of field data for the lower reach of Columbia Glacier, Alaska, U.S.A., indicates that, during the time of the field work, glacier-speed variations in the tidal frequency range are dependent on tidal period variations in sea-level at the terminus, and diurnal period variations in melt-water input at the surface. A simple model based on a perturbation expansion of the flow equation provides a suitable framework in which to understand the observations. Variations in sea- level cause variations in the normal stress at the terminus and are transmitted up the glacier by way of the longitudinal stress. The variations in melt-water input affect glacier speed, presumably through changes in basal water pressure. The data set does not allow a detailed analysis of the relation between melt-water input, basal water pressure, and speed.
The Management of Sediment Transported by Glacial Melt-Water Streams and its Significance for the Estimation of Sediment Yield
Authors: Bezinge A. , Clark M.J. , Gurnell A.M. , Warburton J.
Published: September 2017

This paper describes the calibration of sediment traps in melt-water intake structures of the Grande Dixence hydro-electricity scheme for the purpose of generating medium-term estimates of suspended sediment and bedload transport by pro-glacial streams. The frequency of emptying/purging of sediment from traps in 17 glacier basins in the Val d’Hérens is combined with their design sediment volume to provide first approximations of the mean annual volume of sediment purged. This is followed by more detailed consideration of 11 years of records from three of the basins, to investigate mean seasonal and inter-annual patterns of purging. The difficulties of relating sediment purging to sediment transport are considered. A sediment calibration strategy based on 2 years of turbidity records, hand sampling of suspended sediment concentration, and monitoring of the accumulation of sediment in sediment traps is proposed for one of the glacier basins, and is checked using hourly and 4 h suspended sediment observations from two further ablation seasons. The calibration is applied to 10 years of discharge and purge records to establish estimates of mean seasonal and inter-annual patterns of suspended sediment and bed-load transport.
Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas
Authors: Bogen Jim
Published: September 2017

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.
The Storage of Water in, and Hydraulic Characteristics of, the Firn of South Cascade Glacier, Washington State, U.S.A.
Authors: Fountain Andrew G.
Published: September 2017

The porosity and water saturation of the firn of South Cascade Glacier were measured in order to determine both the volume of water stored in it and the significance of this water content for the water volume stored in the glacier. The distance to water below the firn surface was found never to be greater than 4 m, and the average thickness of the water-saturated layer was estimated to be 1.25 m. The average firn porosity was 0.15, the water saturation was 0.61, and the total volume of water stored in the firn was approximately 1.78 × 105 m3 representing about 12% of the total spring storage. The water table was found to exhibit a pattern of diurnal fluctuation which starts in late June or early July, indicating that melt water from the accumulation zone may pressurize the bed at diurnal frequencies. The depth-averaged permeability was found to be 1.5 × 10−5 m/s, a value which compares favorably with those from other studies.
Assessing Risks from Glacier Hazards in High Mountain Regions: Some Experiences in the Swiss Alps
Authors: Haeberli W. , Alean J.-C. , Müller P. , Funk M.
Published: September 2017

Assessing risks from potential glacier hazards in relation to safety considerations for settlements and other fixed installations in high mountain areas requires the application of experience gained from previous events, combined with simple rules derived from basic glaciological theory. The general characteristics of steep, and usually unmeasured, glaciers can be estimated on the basis of a rough parameterization scheme. Variations in glacier length, ice avalanches, and glacier floods then have to be considered for time periods ranging from a few years up to a few decades. As a result of such systematic assessments, maps of potentially dangerous zones can be prepared. Although the inhabitants of many Alpine villages have always lived with the risk of glacier hazards, it now appears that modern construction work, especially that connected with the development of tourism, has started to infiltrate previously avoided high-risk zones more and more. In order to plan reasonable safety measures, risks from glacier hazards have to be compared with those from other natural hazards in mountain areas, such as snow avalanches, landslides, rock falls! or storm-induced floods. Decisions about the acceptable level of risk are difficult and subjective; they are also often influenced by political and economical considerations rather than by scientific reasoning.