bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Brightness of Polar Firn as Measured by Nimbus 5 and 6 ESMR
Authors: Chang A. T. C. , Choudhury B. J. , Gloersen P.
Published: September 2017

The microwave emission from a half-space medium characterized by coordinate dependent scattering and absorbing centers has been calculated by numerically solving the radiative transfer equation by the method of invariant imbedding. A Mie scattering phase function and surface polarization have been included in the calculation. Also included are the physical temperature profile and the temperature variation of the index of refraction for ice. Using published values of grain-size and temperature-profile data of polar firn, the brightness temperature has been calculated for the 1.55 cm and 0.8 cm wavelengths. For selected regions in Greenland and Antarctica, the results of our calculations are in reasonable agreement with the observed Nimbus-5 and Nimbus-6 ESMR data.
Pressure Waves in Snow
Authors: Brown R. L.
Published: September 2017

A dynamic constitutive law is used to study the response of medium-density snow to shock waves. The results show good correlation between theory and experiment, except for low-intensity shocks which produce small permanent density changes. In this case the validity of the data is questioned, although further experimental work is needed to settle this question. The results of this work also partially explain why snow is so effective in absorbing energy associated with stress waves. This is felt to be due to the work-hardening characteristics of snow.
A Scanning Electron Microscope Examination of Subglacial Quartz Grains from Camp Century Core, Greenland–A Preliminary Study
Authors: Whalley W. B. , Langway C. C.
Published: September 2017

Surface textures and angularity–roundness characteristics of quartz sand grains of till from the base of the Greenland ice sheet at Camp Century were examined with a scanning electron microscope. Two basic populations are revealed; an angular component, which shows grains with edge abrasion and attrition indicative of subglacial grinding, and a well-rounded component with the characteristics of aeolian transport. It is suggested that these two populations were mixed subglacially, the aeolian fraction having been produced at some stage before the ice sheet encroached over the area of their deposition.
The Existence of Multiple Steady States in the Flow of Large Ice Masses
Authors: Fowler A. C.
Published: September 2017

We discuss the possibility of the occurrence of thermal instability in ice sheets and glaciers. This may arise from the non-linear viscous heating term, which could provide for the existence of multiple steady states in the flow and temperature fields: a word of warning is given about the applicability of these ideas.
A Process-Oriented Model for Simulating Avalanche Danger
Authors: Judson Arthur , Leaf Charles F. , Brink Glen E.
Published: September 2017

A simulation process model is developed for rating avalanche danger for twelve east-facing avalanche paths loaded by westerly winds. The model simulates layer age and densification, snow depth, snow transport and deposition, formation of melt crusts, snow temperatures, temperature gradient metamorphism, and avalanche danger on a 6 h basis. Conditioned on avalanches alone, the model predicted avalanche potential on 86% of the 175 avalanche days during an eight-year period. It indicated avalanche potential 50% of the time on non-avalanche days. A sensitivity analysis is under way to improve model performance, and simulation of danger from additional avalanche samples is planned.
Credibility of Avalanche Warnings
Authors: Williams Knox
Published: September 2017

Avalanche warnings can provide a valuable public service. To be effective, the warning program must inspire public confidence. Experience gained from the Colorado Avalanche Warning Program is used to develop guidelines for establishing and maintaining credibility. The topics discussed arc the requirements for a good forecaster, the working relationship between forecaster and field observers, relations with the news media and the public, and forecast accuracy.
A Study on High-Speed Avalanches in the Kurobe Canyon, Japan
Authors: Shimizu Hiromu , Huzioka Tosio , Akitaya Eizi , Narita Hideki , Nakagawa Masayuki , Kawada Kunio
Published: September 2017

Observations and measurements were made of high-speed avalanches at Shiai-dani, the Kurobe canyon, to reveal their real features and properties, using strain-gauge-type load cells in measuring impact force and speed. A maximum impact pressure of 140 × 104 N m-2 was obtained, as well as data indicating the existence of a number of wave fronts, ranging in speed from 9 to 60 m s -1 inside an avalanche. Violent changes in atmospheric pressure ranging from -21 to +5 mbar were observed near its path when a high-speed avalanche passed by.
Empirical Calculations of Snow–Avalanche Run–out Distance Based on Topographic Parameters
Authors: Lied K. , Bakkehøi K.
Published: September 2017

A method for calculation of “maximum” avalanche run–out distance based on topographic parameters only is described. 423 well–known avalanches have had their maximum extent registered. The average gradient of avalanche path (α–angle), measured between the highest point of rupture and outer end of avalanche deposit is used as description of avalanche run–out. The topographic parameters which determine α are described.

A regression analysis of 111 avalanche paths based on 8 terrain parameters is performed, applying 26 independent combinations of these parameters as variables. The four best combinations of variables are used. These variables are: second derivative y’’ of avalanche slope described by a second–degree function, average gradient of avalanche track β, total vertical displacement of the avalanche H, and gradient of rupture zone θ.

The equation has a correlation coefficient of 0.95 and standard deviation of 2.3°. This relationship makes possible a fairly accurate prediction of avalanche run–out distance.
The Acoustic Emission Response of Snow
Authors: St Lawrence William F.
Published: September 2017

In this work a model of the ultrasonic acoustic emission response in snow is developed. The model derived considers the acoustic emission response in snow as a function of stress and strain. It is suggested that the acoustic emission activity in snow is a quantitative indication of the creep rupture taking place in the material. The governing differential equation is developed; an example is then presented that considers the applicability of this equation to the release of certain types of avalanche.
Statistical Models of Snow Strength
Authors: Sommerfeld Richard A.
Published: September 2017

Snow is variable in both time and space. Because of this fact, a complete understanding of snow strength must include statistical strength analyses. Two types of statistical strength theories are the series-element, or weakest-link theories and the parallel-element theories. In the case of snow in shear, Daniels’ (1945) parallel-element theory provides a quantitative explanation of the size and stress-rate relationships of snow, which are at least as accurate as presently available data. In the case of tensile tests, a combination of the two types of theories is proposed which also provides a quantitative explanation which is as accurate as present data. In each case large-volume, low-stress-rate strengths are predicted using small-volume, high-stress-rate data. More data are necessary to provide definitive tests of the proposed hypotheses.
Viscosity and heat transfer in fluidized snow
Authors: Maeno N. , Nishimura K. , Kaneda Y.
Published: September 2017

Fluidized snow was produced in a cold laboratory and its viscosity and heat transfer were studied. The viscosity of the fluidized snow was measured with a modified Stormer-type viscometer. It was found that the apparent viscosity decreased with increasing air velocity and decreasing particle diameter. Two mechanisms were suggested as producing the viscosity of the fluidized snow on the basis of the plot of the viscosity against the reciprocal of the air velocity.

The heat-transfer coefficient was obtained by measuring the temperature of a cooled brass sphere suspended in the fluidized snow. The heat-transfer coefficient in the fluidized snow was three or four times larger than that in an air flow containing no snow particles. The increase was attributed to the enhanced turbulence of air flow and the collision of snow particles; the contribution of the latter was estimated to be 80 to 90% of the total increase due to the fluidization of snow. These results were also confirmed in an artificial blowing snow produced in a cold horizontal wind-tunnel by measuring the heat-transfer coefficient, wind velocity, and drift density.
Mechanical behaviour and structure of snow under uniaxial tensile stress
Authors: Narita Hidek
Published: September 2017

The mechanical behaviour of snow was studied at — 10°C under uniaxial tensile stress in a range of cross-head speed 6.8 × 10–8 to 3.1 × 10–4 ms–1 and snow density 240-470 kg m–3.It was found from the resisting force-deformation curves that the snow was deformed in two different ways: namely, brittle and ductile deformation at high and low strain-rates, respectively. The critical strain-rate dividing the two deformation modes was found to depend on the density of snow. In ductile deformation, many small cracks appeared throughout the entire specimen. Their features were observed by making thin sections and they were compared with small cracks formed in natural snow on a mountain slope.

The maximum strength of snow was found to depend on strain-rate: at strain-rates above about 10–5 s –1, the maximum strength increased with decreasing strain-rate but below 10–5 s–1 it decreased with decreasing strain-rate.
Avalanche-Hazard Mapping and Zoning Problems in the Rocky Mountains, with Examples from Colorado, U.S.A.
Authors: Ives Jack D. , Plam Misha
Published: September 2017

Avalanche-hazard mapping as a basis for land-use decision-making was not undertaken systematically in Colorado until 1974. Passage of Colorado House Bill 1041 required counties to map areas subject to snow avalanche, landslide, debris flow, and mountain flood at 1 : 24 000, and funds were provided. This legislation induced several approaches: work undertaken directly by the Colorado Geological Survey; private contract work; mapping by the Institute of Arctic and Alpine Research (INSTAAR) funded by a NASA research grant. This latter effort produced 37 individual 1 : 24 000 map sheets of Hinsdale, Ouray, San Juan, and San Miguel counties, San Juan Mountains. This emphasized problems of scale and degree of cartographic accuracy. Swiss, Austrian, and French experience, together with the actual Colorado mapping experience, facilitated further definition of problems facing the Rocky Mountains slates, both in terms of resolution of actual mapping problems, and of using such developing experience to influence the decision-making process.

Two mapping attempts are described: (i) development of a combined hazard map for a mountain type area, indicating the difficulties of, and need for, combining hazard assessment of avalanche and other physical processes that frequently overlap; (ii) consideration of avalanche-zoning problems in a wilderness area.

Finally, scale limitations and the need to define rigorously “hazard” are discussed. Definition of hazard must include consideration of recurrence interval, impact pressures in the run-out zone, and limitations of displaying this type of data on available topographic maps, all in relation to types of impact, i.e. to moving or stationary objects in relatively sparsely populated terrane. Additional critical needs facing Rocky Mountains states are itemized: (i) standardized mapping legends for different scales; (ii) establishment of an avalanche cadastre; (iii) systematic reporting of climax events; (iv) development of an historical archive; (v) public awareness; (vi) attention to legal aspects of the avalanche equivalent of the hundred-year flood, and its legal testing.
Observations of Ground Avalanches with a Video Tape Recorder (VTR)
Authors: Akitaya Eizi
Published: September 2017

A description is given and an analysis is made of successful VTR recordings of the process of natural release of eight full-depth avalanches. The observations were made over 7 years on a slope, where avalanches took place. The VTR was capable of taking a visual daytime record of an avalanche in motion for a 12 h sequence per reel.
Swiss Avalanche Hazard Maps
Authors: Frutiger H.
Published: September 2017

This paper describes the various maps concerned with avalanche hazards in Switzerland and gives examples of parts of specimen maps. These include the Wald- und Lawinenkarte der Schweiz (1907) at 1 : 250 000 which marks actual avalanche paths, the Karte der lawinengefährdeten Gebiete (1972) at 1 : 30 0000 which gives a summary view of avalanche hazard, the Gefahrenkarte der Schweiz (1975) at 1 : 100 000 which is intended to give an over-all view of all natural hazards that will influence land use, the Lawinenatlas/Lawinenkarte Uri (1978) at 1 : 25 000 which contains all identifiable avalanche paths in the Canton, the Kombinierte geomorphologische Gefahrenkarte 1: 10 000 von Grindelwald (1977), a Pilot study of mapping natural hazards in a mountain area, and the Lawinengefahrenkarten des Eidg. Institutes für Schnee- und Lawinenforschung at 1 : 10 000 included in 26 advisory reports on 561 individual avalanche paths, and which can act as pilot studies to assist cantons in preparing their own maps.

This paper is being published in full in German in Interpraevent 1980, Bd. 3, as part of the proceedings of the symposium held at Bad Ischl, Austria, 8-12 September 1980.
Gear-Type Glide-Meter as an Instrument For Forecasting Full-Depth Avalanches
Authors: Yamada Yutaka
Published: September 2017

This paper is concerned with the variation of snow glide and its predictability in full-depth avalanches. From field measurements of snow glide using a newly developed gear-type glide-meter which is fixed to the ground and which measures the amount of glide as the angle of rotation of a gear, the following characteristics are deduced: (1) the variation of gliding rate is composed of both short-term and long-term variations, and (2) the existence of correlation between the short-term variation and the relative frequency of avalanches is recognized.
Recent variations of Ghiacciaio del Calderone, Abruzzi, Italy
Authors: Gellatly A. F. , Smiraglia C. , Grove J.M. , Latham R.
Published: September 2017

Results of a detailed topographic survey of Ghiacciaio del Calderone, Italy, the southernmost in Europe, are described and compared with those of surveys made in earlier years. Recession and thinning, much affected by micro-climate, have been the predominant state of health during the 20th century. Between 1916 and 1990, volume is estimated to have been reduced by about 90% and area by about 68%.
Shear-wave detection of asymmetric c-axis fabrics in the GISP2 ice core, Greenland
Authors: Anandakrishnan S. , Fltzpatrick J.J. , Alley R.B. , Gow A.J. , Meese D.A.
Published: September 2017

c-axis fabrics of the GISP2 ice core from central Greenland have been measured rapidly and accurately in the field, using both compressional and shear waves generated by an inexpensive, commercially available, “idiot-proof” device. Compressional-wave data were collected at 10 m intervals for the upper 2250 m of the ice sheet and show progressive clustering of c axes toward the vertical with increasing depth but no large steps at climatic boundaries in the core. The degree of clustering measured by ultrasound agrees closely with that measured using traditional optical techniques but the ultrasound technique is easier and faster than optical methods. A slight asymmetry in the c-axis clustering is revealed by the shear-wave data and increases with increasing depth, indicating that deformation is not symmetric about the vertical at the site.
In-situ measurement of the strength of deforming subglacial till
Authors: Iverson Neal R. , Jansson Peter , Hooke Roger Leb.
Published: September 2017

The shear strength of deforming till beneath Storglaciären, Sweden, was continuously measured with a new instrument, a “dragometer”. A cylinder with conical ends, roughened with till from the glacier bed, was dragged through the till, and the force on the cylinder was recorded. Consistent with studies of cone penetration in soils, it was assumed that the till behaves as a Coulomb plastic material. This allows the residual strength of the till to be calculated from the measured force. Results from laboratory experiments confirm the validity of the analytical procedure.

The average residual strength of the till was ∼55 kPa. A source of error is the potential generation of pore pressure in excess of hydrostatic ahead of the cylinder, which could significantly weaken the till. Calculations indicate that excess pore pressure did not develop during the experiment, but could develop during similar experiments beneath rapidly sliding glaciers with less permeable basal till layers.
Ductile saline ice
Authors: Kuehn G. A. , Schulson E. M.
Published: September 2017

Experiments have shown that tensile ductility of about 5% or more can be imparted to columnar, saline ice by pre-compressing the material by about 3.5%. This effect is similar to that observed in granular, fresh-water ice and is attributed to the operation of both dislocation creep and diffusion creep within that part of the matrix which recrystallized during the pre-compressive deformation.
Instruments and Methods: Direct measurement of sliding at the glacier bed
Authors: Blake W. , Fischer Urs H. , Bentley C.R. , Clarke Garry K. G.
Published: September 2017

Sliding at the base of Trapridge Glacier, Yukon Territory, Canada, was measured using a “drag spool”. We describe this simple and inexpensive instrument as well as its installation and operation. From 1990 to 1992 seven sites were instrumented with drag spools. At six of the sites basal sliding, during the period of observation, accounted for 50-70% of the total flow observed at the glacier surface. The contribution from ice creep is known to be small, so most of the remaining surface motion must be attributed to subglacial sediment deformation. For the seventh site the observed sliding rate was ~ 90% of the total flow, an indication that the sliding contribution varies spatially across the bed. Diurnal variations in the response of one of our instruments appear to be correlated to subglacial water-pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities.
The Effect of Crystal Size and Dispersed-Solid Inclusions on the Activation Energy for Creep of Ice
Authors: Baker Robert W. , Gerberich William W.
Published: September 2017

Steady-state creep-rates of polycrystalline ice were investigated as a function of temperature, grain-size, and inclusion concentration through uniaxial compression in the laboratory. Samples were run at a constant load with the temperature systematically varied between about —5°C and —40°C. The presence of inclusions inhibits dynamic recrystallization and grain growth; the average crystal size produced by recrystallization is inversely proportional to the inclusion concentration. At temperatures above —8°C, creep-rate is enhanced by about a factor of two. This appears to be the result of the combined effects of recrystallization with accompanying grain growth and grain-boundary sliding. Over the temperature range —10°C to —40°C, the apparent activation energy for creep increases with increasing volume fraction of inclusions. This is apparently due to a thermally activated process which is modified by internal stresses created by the inclusions.
Formation, Flow, and Disintegration Of Ice Shelves
Authors: Robin G. De Q.
Published: September 2017

Ice shelves may develop either by continued thickening of sea ice that is held fast to the shore, or by the seaward extension of inland ice. For both processes, as well as for an understanding of ablation and of accumulation at the bottom surface of ice shelves, we need to understand melting and freezing processes in relation to salinity, temperature, and pressure. Consideration of these factors shows that basal melting beneath the thicker parts of ice shelves is much greater than is generally appreciated. This could be sufficient to bring the estimated mass balance of Antarctica into approximate equilibrium. It appears that most Antarctic ice shelves are dependent on the supply of inland ice for their continued existence. However the thick layer of sea ice beneath the Amery Ice Shelf is readily explained in terms of sub-ice water circulation.

Transport of heat and mass by water motion beneath ice shelves has the potential to change ice thicknesses by similar amounts to that caused by internal deformation of the ice shelf. Bottom freezing due to thermal conduction throughout the ice shelf is of minor importance.

While attention is drawn to the basic equations for flow of ice shelves, it is pointed out that they have yet to be applied satisfactorily to the problem of iceberg calving. This appears from field observations to be due primarily to creep failure of spreading ice shelves, possibly aided by impact from floating icebergs. Recent observations show the effectiveness and likely quantitative importance of this “big bang” theory of iceberg formation in Antarctica.

A brief discussion of the effects of climatic change on the disintegration of ice shelves is presented.
Lateral Density Differences from Seismic Measurements at a Site on the Ross Ice Shelf, Antarctica
Authors: Kirchner Joseph F. , Bentley Charles R. , Robertson James D.
Published: September 2017

Seismic compressional-wave data from short refraction shooting carried out during the 1974–75 and 1976–77 seasons at J-9, the site of the Ross Ice Shelf Drilling Project, have been compared. Significant dissimilarities were found to exist between the two sets of data. The measurements were made at locations about 2 km apart, with three unreversed profiles 60° apart recorded during the 1976–77 season and one unreversed profile during the 1974–75 season. The resulting velocity–depth profiles, and hence the derived density–depth profiles, differ by as much as 8%, with the 1976–77 results indicating a maximum velocity, corresponding to solid ice, at a shallower depth than the 1974–75 data. Both profiles were subjected to the same analysis, and a comparison of travel-time curves shows the differences to be real. Densities measured on cores from a 100 m bore hole drilled in 1974–75 about 50 m from the center of the 1974–75 profile agree well with densities computed from that profile. The density difference is believed to be due to the passage of the ice through the high-stress system associated with the interaction between Ice Stream B, flowing in from the West Antarctic ice sheet, and the Ross Ice Shelf. A reversed refraction profile carried out at station B.C. about 30 km up-stream, shows evidence of dipping layers that may be similarly caused.
Seismic Short-Refraction Studies on the Ross Ice Shelf, Antarctica
Authors: Kirchner Joseph F. , Bentley Charles R.
Published: September 2017

Seismic short-refraction studies were carried out at five stations on the Ross Ice Shelf during the 1976–77 summer season as part of the comprehensive Ross Ice Shelf Geophysical and Glaciological Survey. Measurements of the velocities of compressional waves were made at each location. Compressional wave velocities were measured along more than one azimuth at three sites, and shear wave velocities (both components) at two. Travel-time curves were fitted to an exponential expression by means of a non-linear least-squares regression technique. The errors in the apparent velocities are estimated to be about ±50 m s–1 at short distances, diminishing to about ±10 m s–1 near the ends of the profiles. Compressional-wave velocities show only slight variations with azimuth and only over certain depth intervals, showing that constant-velocity surfaces are essentially horizontal. Shear-wave velocities, however, exhibit large variations according to azimuth and polarization, indicating that transverse isotropy is violated at least in the upper 30–40 m of the ice shelf. It is believed that the anisotropy is caused by structural details in the firn perhaps modified by preferred crystal orientation and that it may arise at least partly from anisotropic stresses in the ice shelf.
Mass-Balance Aspects of Weddell Sea Pack Ice
Authors: Ackley S. F.
Published: September 2017

The Weddell Sea pack ice undergoes several unique advance–retreat characteristics related to the clockwise transport in the Weddell Gyre, the physical setting for the pack ice, and the free boundary with the oceans to the north. From satellite-derived ice charts, the annual cycle of the pack ice advance and retreat is depicted. The Weddell pack advance is characterized by a strong east-moving component as well as the north advance seen in other regions such as East Antarctica.

Physical characteristics of the pack ice at the summer minimum ice edge are presented. Indications are that deformation is a significant component of the ice accumulation, deformed ice accounting for c. 15 to 20% of the area covered in the year-round pack. Ablation characteristics are inferred from observations made during field work and from satellite imagery. These observations indicate that surface-melt ablation typically seen on Arctic pack is not seen on the Weddell pack inside the summer edge.

Using the physical-property data and transport inferred from ship and iceberg drifts, a new annual ice accumulation η < 3 m is inferred over the continental shelf in the South compared to η < 2 m previously estimated (Gill, 1973). The implication is that salt flux into the ocean over the shelf may be significantly larger, thereby increasing the production of Western Shelf Water, a component of Antarctic Bottom Water.
A Simple Model to Calculate the Compactness of Ice Floes
Authors: Neralla V. R. , Liu W. S.
Published: September 2017

This paper describes a simple model for predicting compactness over a given area. The model incorporates equations of continuity and momentum. The momentum equation is based on a balance between air-ice stress, water–ice stress, Coriolis force, and internal ice resistance. Since our interest is in short-range small-scale prediction, as a first step we have neglected sources and sinks terms in the continuity equation and assumed ice to be a film of Newtonian highly-viscous fluid. The solution of a simple equilibrium formulation is used as initial conditions.

Surface winds over the area of interest are obtained from an available model developed on the basis of similarity theory. The compactness model has been applied for a few real cases in summer 1975 over the Beaufort Sea area. The preliminary results of the model are encouraging. The main advantage of this model is that it can run on mini-computers available at most forecasting centres.
Stability of Glaciers and Ice Sheets Against Flow Perturbations
Authors: Thompson David E.
Published: September 2017

A stability equation is derived for a model glacier of initially uniform thickness and of infinite extent transverse to the primary flow flowing without slip down an inclined plane. A stress-dependent power-law viscosity is wholly incorporated into the equations of motion. Stability of the glacier is tested against long-wavelength surface perturbations. Results for this initial formulation indicate that the glacier is stable against infinitesimal amplitude surface perturbations, although for certain variations of model parameters, the decay-rate of the disturbance becomes very slow, approaching neutral stability. Results are presented in terms of decay-rate magnitudes over a large range of perturbation wavelengths for many model glaciers in which bed slope, ice thickness, and ice rheology parameters are varied. For all models, the maximum decay-rate of the perturbation occurs at disturbance wavelengths of roughly three to six times the glacier thickness. Infinite-wavelength perturbations are found to be only neutrally stable. Long-wavelength perturbations propagate at a faster rate down-glacier than do the intermediate- or shorter-wavelength ones which tend to remain fixed on the glacier surface andride down-glacier with the primary flow as they decay.
Ice-Sheet flow in the Vicinity of Southern Victoria Land, Antarctica: Implications for Glacial Chronology
Authors: Drewry David J.
Published: September 2017

Systematic radio echo-sounding during three seasons since 1971–72 has produced data on the configuration of the ice sheet in East Antarctica. In the sector extending inland from southern Victoria Land, the ice sheet exhibits a large ridge which drives ice towards David Glacier in the north and Mulock and Byrd Glaciers to the south. Within 100 km of the McMurdo dry-valley region soundings along ten sub-parallel lines (c. 10 km apart) provides detail on ice surface and flow patterns at the ridge tip. A small surface dome lies just inland of Taylor Glacier. The surface drops by 100 m or more before rising to join the major ridge in East Antarctica.
Flow Of Antarctic Ice Shelves Between Long. 29° E. And 44° W
Authors: Orheim Olav
Published: September 2017

This paper discusses the mass outflow and dynamics of a 3000 km long front of the Antarctic ice sheet—the coastline from Prinsesse Ragnhild Kyst to the Filchner Ice Shelf. Ice shelves, mostly 50–100 km wide, account for more than 95% of this coastline. Large mass losses by calving generally occur at intervals of several decades at any particular location, and usually involve shelf areas of 10-1000 km2. The mass loss by calving during the periods between the large calvings is insignificant, except where ice streams run directly into the sea without forming ice shelves. The latter sections account for 2% of the coastline in question and a similar part is made up of ice rises. Thus, with the exception of these short segments, the ice front advances systematically over time intervals of a few decades. Large calvings interrupting the advance can be recognized by significant change in shape and position of the ice front.
Ice-Sheet Surface Elevation and Changes Observable by Satellite Radar Altimetry
Authors: Zwally H. Jay , Brooks R. L. , Stanley H. Ray , Campbell W. J.
Published: September 2017

A major question in ice-sheet dynamics is the state of balance between the net mass input and ice flow. Since an imbalance produces a change in surface elevation, the state of balance can be studied by monitoring the elevation, and this has been accomplished by surface-leveling techniques in a few locations. Due to the requirement for accurate and repetitive measurements over large areas, it is not practical to determine the status of balance of an entire ice sheet or even a major drainage basin by conventional techniques. Now, recent results from satellite-borne radar altimeter measurements over the Greenland ice sheet demonstrate the feasibility of accurately measuring and monitoring the topography of large ice masses. The application of this new technique offers the possibility of making a meaningful mass-balance determination and for detecting actual or potential ice-sheet surges.
Predicting the Motions of Drifting Open Pack Ice
Authors: Feldman Uri , Howarth Philip J.
Published: September 2017

Methods based on remotely-sensed data are needed to predict motions of drifting open pack ice and to determine sea-ice parameters associated with these motions. The method presented here is able:

(a)

to predict the motions of groups of wind-driven detached ice floes over periods of 12, 36, and 60 h;

(b)

to determine sea-ice thickness and the surface and sub-surface drag coefficients associated with these motions.
Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier
Authors: Bindschadler Robert
Published: September 2017

For the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation
1
where
H is the local depth, and ys and yb are the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factor f is included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that when T is averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2G can then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), where τb and 2G are estimated as

and

at intervals of 100 m, Us is the measured surface center-line velocity, A and n are the flow-law parameters, and is the surface longitudinal strain-rate. The expression for 2G is an approximation proposed by Budd (1970).
The Mass Budget of the Lambert Glacier Drainage Basin, Antarctica
Authors: Allison Ian
Published: September 2017

Estimates have been made of the mass budget of the total drainage basin of Lambert Glacier. These show a small but significant positive state of balance for the interior basin (the accumulation area up-stream of the major ice streams) and strongly suggest a positive balance for the Lambert Glacier system (the region of major ice streams, between the Amery Ice Shelf and the interior basin). The total mass flux into the interior basin is estimated as 60 Gt a–1. Results are presented from a number of ice movement stations established between 1972 and 1974 around the perimeter of thesouthern Prince Charles Mountains. These results, together with ice thicknesses from radio echo-sounding in the area, give a total mass outflux through the 2000 m contour of 30 Gt a–1, implying a budget excess of a further 30 Gt a–1 over the whole interior basin. Results from velocity and ice-thickness measurements give a mass discharge through a section near the junction of Lambert Glacier and the Amery Ice Shelf of 11 Gt a–1. Losses within the Lambert Glacier system proper account for a further 7 Gt a–1 and an overall mass excess of 12 Gt a–1 is estimated for the Lambert Glacier system. This present positive state of balance contrasts with geomorphological evidence from the southern Prince Charles Mountains of a large drop in ice level in recent geological time, and the ice surface in the area may now be building up after a major recession.

This paper has been published in full in Journal of Glaciology, Vol. 22, No. 87,1979, p. 223—35.
Determining the extent of pressurized flow beneath Storglaciären, Sweden, using results of tracer experiments and measurements of input and output discharge
Authors: Kohler Jack
Published: September 2017

Two experiments were conducted on the drainage system beneath the Lower part of the ablation zone of Storglaciären, a small valley glacier in northern Sweden. In the first experiment, over 70 tracer tests were performed in a cluster of moulins during a 1 month period, at sub-daily intervals. In the second experiment, input- and output-discharge signals were measured on the supraglacial melt stream emptying into a moulin and on the proglacial stream to which the moulin drains. The data from these two experiments are used in an idealized model of the subglacial drainage system to calculate the percentage of the system flowing as an open channel. Results from the tracer experiment suggest that the system is pressurized to within 60-340 m of the snout, while analysis of the discharge data indicates pressurized ronduits to within 0-415 m of the snout.
Characteristics of tide-water calving at Glaciar San Rafael, Chile
Authors: Warren Charles R. , Glasser Neil F. , Harrison Stephan , Winchester Vanessa , Kerr Andrew R. , Rivera Andres
Published: September 2017

Glacial calving is a poorly understood process. This study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at Glaciar San Rafael, Chile. Near the terminus of the glacier, surface speeds average 17 m d−1in summer and calving is profuse and continual. The size, location and characteristics of over 7000 calving events were recorded during 32d in 1991 and 1992, together with meteorological, bathymetric and oceanographic data. Mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 Mm3d1. Mean annual calving speed and calving flux are about 4500 m a−1and 2.0 km3a−1, respectively. This calving speed is higher than that predicted by the established empirical relationship between tide-water calving speed and water depth. This is surprising, given the low salinity of Laguna San Rafael and that fresh-water calving speeds are commonly much lower than those in ride water. Daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables, but tidal stage may have some control over the timing of large submarine calving events. Submarine calving produced the largest bergs. However, the relatively small total flux recorded from the submerged pars of the ice cliff may imply unusually rapid melt rates.
Monthly balance and water discharge of an inter-tropical glacier: Zongo Glacier, Cordillera Real, Bolivia, 16° S
Authors: Francou Bernard , Ribstein Pierre , Saravia Ronald , Tiriau Eric
Published: September 2017

Measurements of mass balance were performed every month on Zongo Glacier. Bolivia. Simultaneously, water-discharge, temperature and precipitation data were obtained. The first year of the survey, 1991–92. was marked by an ENSO (El Niño-Southern Oscillation) event with high temperature and low precipitation, whilst the following year, 1992–93, was normal. Results point to the early and late wet season (October-December and March–May: as playing a critical role in the determination of the annual mass balance. The wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance. Both glaciological and hydrological methods for the determination of the mass balance provide similar results. Our study confirms dial ENSO events have a major influence on the rapid glacier retreat currently affecting this part of the Andes.
Short-pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of Matanuska Glacier, Alaska, U.S.A.
Authors: Arcone Steven A. , Lawson Daniel E. , Delaney Allan J.
Published: September 2017

Wavelets transmitted by short-pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of Matanuska Glacier, Alaska, U.S.A. The field studies were in the ablation region, where radar horizons could, at some point, be identified with interfaces between clear ice and air, water or basal ice, and were performed in early spring before drainage fully developed. The profiles used closely-spaced antennas with bandwidths centered near 50 and 400 MHz. Transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts. Migration and Fourier-transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections. Interfacial dielectric contrasts are determined from the relative phase of the wavelets. Near the terminus lake, some basal ice events above 8 m depth are interpreted as voids. Further up-glacier, most englacial events are interpreted as voids, but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids, water or debris. Phase cannot be determined for the basal-substrate transition reflections. Recommendations are made for improving the wavelet recovery process and the quality of GPR migration.
Characterization and flexural strength of iceberg and glacier ice
Authors: Gagnon R.E. , Gammon P.H.
Published: September 2017

Flexural strength of iceberg and glacier ice was determined from Four-point beam-bending experiments. A large quantity of glacial ice was collected from four icebergs and one glacier, and a detailed ice-characterization program was performed on samples from the five sources. Beam-bending experiments were conducted at four temperatures in the range −1 ° to-16 °C and at strain rates of 10 −3 and 10−5 s−1. The flexural strength was found to increase with increasing strain rate (based on extreme fibre strain and decreasing temperature. The data suggest than air-bubble inclusions play an important role in determining the flexural strength of glacial ice and this can explain the significant differences in mean strength of the ice from the five sources. At a strain rate of 10−3 s−1 and temperature of —11 °C, the flexural strength was found to increase as the number of bubbles per unit volume increased. Reduction of crack-initiating stresses at grain boundaries by “softening” of grains due to intragranular air-bubble inclusions is thought to be the mechanism.
Response of valley glaciers to climate change and kinematic waves: a study with a numerical ice-flow model
Authors: van de Wal R. S. W. , Oerlemans J.
Published: September 2017

A simple numerical flow model that couples mass divergence directly to basal shear stress as the only driving force is used to study kinematic waves. Kinematic waves that result from a perturbation of the ice thickness or mass balance are compared with the linear kinematic-wave theory of Nye/Weertman. The wave velocity is calculated as a function of the wavelength and amplitude of a perturbation. The modelled wave velocity is typically 6–8 times the vertically averaged velocity in the flow direction whereas linear theory predicts a factor of only 5.

An experiment with the geometry of Hintereisferner, Austria, shows that the increase in the local ice velocity during a kinematic wave is about 10% but varies slightly depending on the position along the glacier and the amplitude of the kinematic wave. Kinematic waves are thus hard to detect from velocity measurements.

The dynamics of simple continuity models are rich enough to support a variety of kinematic-wave phenomena. Such models are a useful tool to study the response of valley glaciers to climate change.
Variations of ablation, albedo and energy balance at the margin of the Greenland ice sheet, Kronprins Christian Land, eastern north Greenland
Authors: Konzelmann Thomas , Braithwaite Roger J.
Published: September 2017

A meteorological and glaciological experiment was carried out in July 1993 at the margin of the Greenland ice sheet in Kronprins Christian Land, eastern north Greenland. Within a small area (about 100 m2) daily measurements were made on ten ablation stakes fixed in “light” and “dark” ice and were compared to each other. Simultaneously, the components of the energy balance, including net radiation, sensible-heat flux, latent-heat flux and conductive-heat flux in the ice were determined. Global radiation, longwave incoming radiation and albedo were measured, and longwave outgoing radiation was calculated by assuming that the glacier surface was melting. Sensible-and latent-heat fluxes were calculated from air temperature, humidity and wind speed. Conductive-heat flux in the ice was estimated by temperature-profile measurements in the uppermost ice layer. Net radiation is the major source of ablation energy, and turbulent fluxes are smaller energy sources by about three times, while heat flux into the ice is a substantial heat sink, reducing energy available for ice melt. Albedo varies from 0.42 to 0.56 within the experimental site and causes relatively large differences in ablation at stakes close to each other. Small-scale albedo variations should therefore be carefully sampled for large-scale energy-balance calculations.
Mapping c-axis fabrics to study physical processes in ice
Authors: Alley R. B. , Gow A.J. , Meese D.A.
Published: September 2017

Mapping the spatial distribution of c-axis orientations in ice thin sections is not much more difficult than preparing c-axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice. Distributions of angles between c axes of neighboring grains from the Byrd Station (West Antarctica) ice core suggest that polygonization causes average grain-size to stabilize below 400 m depth.
Electrical Resistivity Measurements on Ice Sheets
Authors: Hochstein M.
Published: September 2017

The electrical resistivity of firn and ice of ice sheets is a function of the “base” resistivity, the contact resistance between the grains, and the temperature. At greater depths temperature is the predominant influence, and observed resistivity curves can be explained by temperature variations which agree partly with the theories of heat conduction in ice sheets.
Ice–Brine Dendritic Aggregate formed on Freezing of Aqueous Solutions
Authors: Rohatgi P. K. , Adams C. M.
Published: September 2017

Dendritic aggregates of ice and brine formed upon freezing of aqueous solutions have been studied. Chlorides of sodium, potassium, lithium and hydrogen were used as solutes; structures produced on freezing of binary, ternary and quaternary solutions were examined. Effects of freezing rate, solute concentration, solute diffusivity, mixing of solutions and magnetic fields are reported.

The spacing between ice platelets or dendrites was found experimentally to be proportional to the square root of the freezing time when the freezing rate was constant from beginning to end of solidification. During unidirectional freezing from a constant temperature chill, the solution at each location is subjected to a spectrum of freezing rates; dendrite spacing increases linearly with distance from the chill surface and it is inversely proportional to the square root of the maximum freezing rate.

In binary solutions dendrite spacing increases linearly with solute concentration; above a critical solute concentration ice platelets develop side branches. Application of an external magnetic field has an effect similar to increasing concentration. At a given solute concentration, spacing between ice dendrites increases linearly with solute diffusivity.

In ternary and quaternary solutions dendrite spacing is a function of the concentrations and diffusivities of each of the constituent solutes.
Mass-Balance Studies of Gara Glacier
Authors: Raina V. K. , Kaul M. K. , Singh Surinder
Published: September 2017

The Gara Glacier, a north-facing valley glacier situated in the western Himalaya, was selected to be part of the study undertaken by India in connection with the International Hydrological Decade. This paper deals with the procedure adopted and the results obtained for mass-balance assessment over a period of one year between September 1974 and September 1975. The glacier has recorded a positive net balance of the order of 2.48 X 106 m3 in terms of water equivalent.
An experimental study of the glacier boundary layer over melting ice
Authors: Munro D. S. , Davies J. A.
Published: September 2017

The results of an experiment to examine the glacier boundary layer over melting ice are described. They show that the boundary layer, as defined by the applicability of the log—linear profile, is approximately 1 m thick. The boundary layer is a frequent, but not a dominant feature of the air close to the ice. The frequency of occurrence is relatively high in cases where wind speeds are mainly controlled by katabatic forces.