bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 iswith 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.
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.
Hydrological Investigations at Biafo Glacier, Karakoram Range, Himalaya; an Important Source of Water for the Indus River
Authors: Hewitt K. , Wake* C.P. , Young G.J. , David C. 
Published: September 2017

Over 80% of the flow of the Upper Indus River is derived from less than 20% of its area: essentially from zones of heavy snowfall and glacierized basins above 3500 m elevation. The trans-Himalayan contribution comes largely from an area of some 20 000 km2 of glacierized basins, mostly along the axis of the Greater Karakoram range and especially from 20-30 of the largest glacier basins. Very few glaciological investigations have so far been undertaken in this the major glacierized region of Central Asia. Biafo Glacier, one of the largest of the Karakoram glaciers, drains south-eastwards from the central Karakoram crest. Its basin covers a total area of 853 km2, 628 km2 of which are permanent snow and ice, with 68% of the glacier area forming the accumulation zone. This paper describes investigations of snow accumulation, ablation, glacier movement, and glacier depth undertaken in the period 1985–87, set against a background of investigations carried out over the last 130 years. Biafo Glacier differs from most of the other Karakoram glaciers in being nourished mainly by direct snowfall rather than by avalanching; this has the advantage of allowing extensive investigation of accumulation over a broad range of altitude.Snow-accumulation studies in the Biafo Glacier basin have indicated that annual accumulation varies from 0.9 to 1.9 m of water equivalent between 4650 and 5450 m a.s.l. This suggests an annual moisture input above the equilibrium line of approximately 0.6 km3. Monopulse radar measurements indicate the presence of ice thickness as great as 1400 m at the equilibrium line, although these results may not be completely reliable. Mean surface velocity during the summer of 0.8 m d−1 has been measured near to the equilibrium line. Calculations of annual ice flux through the vertical cross-profile at the equilibrium line indicate a throughput of 0.7 km3 a−1. Estimates from stake ablation measurements also suggest that ice loss on Biafo Glacier is about 0.7 km3 a−1. The close agreement between these three sets of measurements is reassuring, indicating that the ablation zone of Biafo Glacier, whose area covers 0.09% of the whole Upper Indus basin, produces approximately 0.9% of the total run-off. However, it should be mentioned that this estimate does not include water originating from seasonal snow melt, either above or below the equilibrium line, or from rainfall. Net annual ice losses due to wastage of the glacier since 1910 are probably of the order of 0.4-0.5 m a−1; this would represent between 12 and 15% of annual water yield from melting ice.
Experimental Studies on a Powder-Snow Avalanche
Authors: Kawada K. , Nishimura K. , Maeno N. 
Published: September 2017

To make clear the structure and behaviour of a large-scale avalanche, the impact force-data obtained in the avalanche project of 1972–78 were analysed in detail. The wave forms of impact forces are classified into two types. Type 1 is composed of many separate spikes each of which represents the collision of a snow block. Type 2 has wider peaks, caused by collisons of snow blocks mixed with fluidized snow. Most of the type 1 peaks were in the width range corresponding to 0.005–0.01 s duration, and most type 2 peaks fell into the 0.02–0.1 s range.The internal velocities of an avalanche were estimated by calculating cross-correlation spectra for a time series of impact-force records. It was discovered that these internal velocities varied from 10 to 50 m/s over time. The mean distance between snow blocks was found to be in the range 1.6–5.4 m in a type 1 avalanche, and between 0.7 and 3 m in type 2 avalanches. Sizes of snow blocks or snow clouds of type 1 and type 2 were in ranges 0.26–0.52 and 0.37–1.9 m, respectively.This paper also reports on the project created to initiate artificial powder-snow avalanches in the Shiai-dani area and to make systematic observations of a variety of physical aspects. Results obtained in 1988 for both artificial and natural avalanches are given.
Modelling Global Ice and Climate Changes Through the Ice Ages
Authors: Budd W.F. , Rayner P. 
Published: September 2017

A global energy balance model has been developed which includes an interactive mixed layer ocean, sea ice, and snow and ice cover on the land. A full annual cycle is included and the model provides a close simulation to the variation of surface temperature through the year over land and over ocean as a function of latitude. The present annual variations of sea ice and snow on the ground are also well simulated. The model has been used for a wide range of sensitivity tests which include variations of the solar constant, surface albedos, and the effects of feed-back, or absence of feed-back, in the reponse of the snow and ice cover.Studies have been made of the model’s response to the long term variations in the Earth’s Orbital characteristics such as changes in the perihelion, the obliquity and the eccentricity as well as various combined changes. Independent sensitivity studies of the response of the model to the presence of the large ice sheets in the northern hemisphere have also been carried out. A series of model runs have been performed to study climatic changes around the globe from 160 000 years Β.P. (Before Present) to the present. An examination is made of the impacts of the orbital changes alone, as well as with the feed-back from the large ice sheets.
Climatic Effects on Glacier Distribution Across the Southern Coast Mountains. B.C., Canada
Authors: Evans Ian S. 
Published: September 2017

Over a distance of 150 km inland across British Columbia, glaciation level (altitudinal threshold for glacier generation) rises north-eastward from 1800 m near Jervis Inlet, to 2800m near Lillooet on Fraser River. The methods of Østrem (1966b) are revised for more detailed work from air photographs; inclusion of small but active glaciers gives a glaciation level some 200 m below Østrem’s from 1:250 000 maps, or 110 m below that from 1:50 000 maps.Mountains which rise slightly above the altitudinal threshold invariably support glaciers only on their northerly slopes. Mountain crests need to be some 300 m higher before they support glaciers on most slopes: this defines an “all-sided” glaciation level. Since summit heights vary from 2500 to 2900 m through most of the transect considered here, east- and west-facing glacier sources are found mainly in the coastal half; south-facing sources are rare outside icefields.For particular mountain ranges bounded by valleys and low passes, the aspects (azimuths) of glacier sources can be summarised by vector analysis. The higher the range rises above glaciation level, the more widespread the aspects represented and the weaker the resultant vector strength. Strengths as high as 90% are observed on landward ranges with a relatively sunny, continental climate, while 20-60% is found for coastal ranges where cloudiness reduces slope variations in incident solar radiation. Vector mean aspects throughout are close to north.Perennial lee drifts on icefields show that wind directions during and immediately after snowfalls are from the south or from south-south-west. Together with orographic details of the glaciation level, this suggests that snow-bearing winds come from the south rather than the west. These winds reinforce radiation contrasts, giving north-south asymmetry of glacier aspect even near the coast.
Antarctic and Southern Ocean Sea-Ice and Climate Trends
Authors: Jacka T.H 
Published: September 2017

A computer-based climate monitoring project is described. Data sets include monthly and annual mean surface temperatures and pressures for occupied stations in Antarctica, the Southern Ocean and South Pacific Ocean; and monthly Antarctic sea-ice extent at each 10° of longitude.Simple statistical analyses of the data sets reveal a mean warming of ~0.15°C (10 a)−1 since the mid 1950s for Antarctic coastal stations and of ~0.04°C (10 a)−1 since the mid 1940s for the ocean stations. The sea-ice record from 1973 to 1988 reveals that the average northern ice limit has decreased at ~0.23°lat. (10 a)−1. Despite apparently compatible long-term trends of temperature and sea-ice extent, annual fluctuations of temperature and ice extent are highly variable and are not well correlated.
A Review of Central Asian Glaciochemical Data
Authors: Wake Cameron P. , Mayewski Paul A. , Spencer Mary Jo 
Published: September 2017

The glaciers of central Asia provide suitable locations from which to recover continuous, high-resolution glaciochemical records on a continental scale. Although the glaciochemical investigations undertaken to date in central Asia are few in number and limited in terms of spatial coverage and length of record, some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region.The sodium chloride ratio for most snow samples collected in central Asia approaches the ratio found in sea water (0.86 in μeq kg−1), reflecting a marine source for these constituents. Sodium and chloride concentrations are, on average, 3–10 times higher in the Himalayas than in the Karakoram, demonstrating the greater influence of monsoonal sources of moisture in the Himalayas. Very high sodium concentrations from Khel Khod Glacier probably reflect a local crustal source from surrounding ice-free areas. Low nitrate concentrations were found in snow collected from the southern margin of the Himalayas and high concentrations in snow deposited on the north margin of the Himalayas. This strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols, rich in nitrate, originating from the arid regions of central Asia. High calcium concentrations measured in snow from Mount Everest and the north-west corner of China are also indicative of dust derived from the arid regions of central Asia. Very high sulfate concentrations found in snow from the Tien Shan and the Bogda Shan most likely reflect local anthropogenic sources. The altitude effect on isotopie composition is not apparent from snow samples collected in central Asia.Understanding the processes which control the chemical content of snow, the local-to-regional scale complexities, and the seasonal variability are fundamental steps necessary to assess the potential for recovering representative long-term glaciochemical records from central Asia.
The Mass Balance Of Blue Glacier, Washington, U.S.A. 1956–1986
Authors: L. Armstrong Richard 
Published: September 2017

Mass-balance data for Blue Glacier are presented for the 31-year period 1956–86. The glacier location is strongly maritime with annual precipitation of 3500 to 5000 mm, most of which falls as winter snow. The low elevation of the glacier results in large amounts of summer ablation and thus significant annual mass exchange. Blue Glacier has been in approximate equilibrium with recent climate during the past 30 years with a slightly positive mean annual net balance of 0.3 m and a terminus advance of 150 m. Comparison with other glaciers in western North America indicates that this pattern of mass increase in response to recent climate is not typical but may be specific to a maritime location.Due to heavy amounts of winter snowfall, an accumulation area ratio of only 0.5 is sufficient to maintain a zero balance on Blue Glacier. A strong gradient of increasing snowfall with elevation contributes to a linear relationship between net balance and elevation throughout the total altitude range of the glacier. This relationship is consistent over the period of record and is not dependent on an overall net positive balance, as the pattern persists even during periods of strongly negative mass balance. A relationship between measured mass balance and equilibrium-line altitude provides a reasonable method to compute mass balance.
Determination Of Snow Facies and Ice Velocity Using Synthetic Aperture Radar Imagery
Authors: Bindschadler R.A. , Vornberger P.L. 
Published: September 2017

The properties of synthetic aperture radar (SAR) imagery are appropriate for its use to map snow facies. These facies, defined by Benson (1962), are subdivisions of the accumulation area of an ice sheet or polar glacier and represent the interaction of the ice mass with the climate through the processes of snow accumulation and melting. Changes in these climatic parameters are expected to cause changes in the extent and character of these facies. The ability of SAR to discriminate these facies is due to the significant amount of sub-surface volume scattering in the measured radar backscatter signal and the strong absorption of radar energy by liquid water. The amount of volume scattering is dependent on the size and distribution of scatterers in the medium. This dependence varies over the size range of snow grains to ice lenses. Specific examples of the ability to detect different scatterer populations in ice sheets with SAR are shown. Other examples are given to demonstrate the reduction of backscatter signal when liquid water is present.Another important application of SAR data is the determination of surface velocity. Coregistration of a SAR and a TM image spanning an eight-year period was completed for an area in south-western Greenland. The composite image shows that, while the network of surface streams is nearly unchanged, their distance from lakes upstream increased over the eight-year interval between images. Because the lakes are likely fixed in space, a result of surface depressions whose positions are determined by the stationary bedrock topography, the displacement of the stream network was used to calculate a surface velocity of 40 ± 10 m per year near the equilibrium line.
A Eurasian Ice-Sheet Study Using A Combined Ice-Sheet/ Ice-Shelf Numerical Model
Authors: Lindstrom Dean R. 
Published: September 2017

A numerical model which simultaneously computes grounded and ice-shelf flow was used to develop an equilibrium ice-sheet–ice-shelf system over Eurasia and the Arctic region. Present-day net accumulation rates and mean annual and July temperature values were used as base values for climatic variable specifications. The values were adjusted during the model run to account for changes in the ice-surface elevation and atmospheric CO2 concentration. The model-determined equilibrium ice-sheet configuration was used as input for additional runs to observe what effect removing the Arctic ice shelf and increasing the CO2 concentration from glacial to present-day values has on the ice sheet.At equilibrium, an ice shelf formed over the Arctic Ocean and Greenland and Norwegian seas. Ice easily grounded over the Barents, Kara, East Siberian, and Laptev seas. The grounded ice-sheet profile differs in Europe from most glacial geological reconstructions because the North Atlantic Current effect was not removed from the climatic adjustments. As a result, ice did not extend over the North Sea and onto the British Isles because of the North Atlantic Current's warming effect. Also, the precipitation rate over Europe was too high because of the moisture source the North Atlantic Current carries, and the ice sheet expanded beyond the field-determined ice-sheet margins in the region south-east of Finland.Removing most of the Arctic region's ice-shelf cover had little effect on the grounded ice sheet unless it rested upon a deformable sediment layer. The ice sheet was able to collapse within 10 000 years, however, when the CO2 concentration was gradually increased toward present-day values using the Vostok ice core's CO2 record from the last 18 000 years. Initially, most mass loss resulted from surface melting. Once the thickness decreased enough over some regions for the grounded ice to become ungrounded, however, most mass loss resulted from the ice shelf rapidly transporting the ice to the ice-shelf front and discharging it to the sea.