bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Studies on Densification and Pressure-Sintering of Ice
Authors: Ebinuma Takao , Maeno Norikazu
Published: September 2017

Pressure-sintering experiments of ice particles were carried out at pressures between 0.1 and 2.0 MPa and temperatures between -25 and -9°C. At each experiment, logarithm of the strain rate of densification was proportional to the density, and the slope of proportionality changed at a critical density implying the alternation of predominant densification mechanisms. The critical density varied with applied pressure and temperature, but its variation was restricted between 700 and 750 kg/m3.

At densities below the critical density, two-dimensional coordination numbers of constituent particles increased though specific areas of internal free surface were almost constant. The result was explained by the predominant contribution of the process of particle rearrangement in this density range. On the other hand, the contribution of dislocation creep was concluded to be dominant at densities above the critical density; the creep caused by boundary diffusion also contributes especially at higher densities.
Characteristics of Flowing Snow and Avalanche Impact Pressures
Authors: McClung D. M. , Schaerer P. A.
Published: September 2017

Experimental data on avalanche impact pressures and speeds from an avalanche path at Rogers Pass, B.C., are presented for both dry and wet avalanches. Data from small load cells (645 mm2 surface) at various heights through the vertical cross-section of the avalanches show that the frequency of particle impact and hence flow density increases rapidly from top to bottom of the flow.

Data from a large circular impact plate (196 000 mm2) just above the ground surface show that dry avalanches have relatively higher peak pressures and relatively lower average pressures than wet avalanches for a given speed. Longitudinal wave-like characteristics in the flow may be seen for both wet and dry avalanches, but they appear to be the exception rather than the rule.

Comparison of pressure results with those of other studies shows good agreement for peak pressures, but average pressures are generally less than those of previous studies. This discrepancy is attributed to the past use of cells for which loading surface size approached typical particle size. The size effect may be demonstrated by comparison of small cell data with results from the large impact plate at Rogers Pass.
Settlement Force on a Beam in Snowpack by Computer Modelling
Authors: Lang Theodore E. , Nakamura Hideomi , Abe Osamu
Published: September 2017

Computer analysis is carried out to predict the force that bears upon a horizontal beam embedded in settling snowpack. Use is made of extensive experimental data on snow depth, layering and density, and on measured force on a test beam, in order to evaluate the internal structural arrangement in a finite element representation of the region in the vicinity of the beam. The compressive secondary-creep viscoelastic properties and the densification properties of the snow are accounted for in the computer modelling. Results show that the bearing force on the beam develop from direct snow weight, from shear transfer by adjacent snowpack, from basal weakening below and to the side of the beam, and from snow densification above and to the side of the beam producing a bridging mechanism. These findings corroborate with related experimental results and point out the need for further refinement in definition, particularly of the bridging mechanism, which produces large force incrementation on the beam compared to the other mechanisms noted.
Relict flow stripes on the Ross Ice Shelf
Authors: Casassa G. , Jezek K.C. , Turner J. , Whillans I.M.
Published: September 2017

Analysis of AVHRR data collected during the summer and winter over the Ross Ice Shelf reveals complex patterns of curvilinear stripes. In particular, a large, looping pattern of stripes is observed west of Crary Ice Rise in an area where conventional glaciological data collected with surface and airborne methods have been interpreted to suggest uncomplicated flow. On the basis of previous work using radar data to study ice flow downstream of Crary Ice Rise, we conclude that the stripes represent relict flowlines. The mechanism that produces these stripes is unclear, but we hypothesize that they are associated with subtle topography. Based solely on the patterns of stripes and their location in the outflow of major ice streams, we propose that they are related to an ice raft torn from the grounded ice sheet about 400 km upstream from its present position.
Mesoscale eddy formation and evolution in the ice-covered ocean
Authors: Ikeda Motoyoshi
Published: September 2017

Generation mechanisms of mesoscale eddies in the ice-covered ocean are studied by using numerical ice–ocean models and discussed with reference to previous papers. The three possible mechanisms of eddy generation, with sea ice as a passive tracer, are current instability, current-eddy interaction and current–bottom topography interaction. The current instability, categorized into barotropic and baroclinic instabilities, may be responsible for eddies near the ice edge associated with a strong current. An eddy can interact with a current, producing additional eddies, where stability of the current is again an important factor for eddy formation. Eddies over bottom topography on the continental shelf are explained by current–topography interaction; i.e. anticyclones are produced over banks. The particular mechanism that includes ice as an active material is an ice–ocean interaction; i.e. a wind stress is larger over the ice than on open water and induces Ekman pumping and suction, which produce dipole eddy motions in the non-uniformly ice-covered ocean. The eddies are suggested to be important for cross-shelf exchanges of ice and heat as well as determining locations of deep convection.
On the effect of rheology on seasonal sea-ice simulations
Authors: Ip Chi F. , Hibler William D. , Flato Gregory M.
Published: September 2017

A generalized numerical model which allows for a variety of non-linear rheologies is developed for the seasonal simulation of sea-ice circulation and thickness. The model is used to investigate the effects (such as the role of shear stress and the existence of a flow rule) of different rheologies on the ice-drift pattern and build-up in the Arctic Basin. Differences in local drift seem to be closely related to the amount of allowable shear stress. Similarities are found between the elliptical and square cases and between the Mohr-Coulomb and cavitating fluid cases. Comparisons between observed and simulated buoy drift are made for several buoy tracks in the Arctic Basin. Correlation coefficients to the observed buoy drift range from 0.83 for the cavitating fluid to 0.86 for the square rheology. The average ratio of buoy-drift distance to average model-drift distance for several buoys is 1.15 (square), 1.18 (elliptical), 1.30 (Mohr-Coulomb) and 1.40 (cavitating fluid).
Application of an atmospheric boundary layer model to a large-scale coupled sea-ice-oceanic mixed-layer model for the Southern Ocean
Authors: Stössel Achim
Published: September 2017

A coupled sea-ice-oceanic mixed-layer model for the Southern Ocean is forced with daily atmospheric variables from the global analyses of the European Center for Medium Range Weather Forecasts (ECMWF). Using the analyses of the lowest level in the calculations of the turbulent heat fluxes and stresses with the appropriate bulk formulae, the simulation results resemble earlier ones with climatological forcing. In order to avoid a predetermination of the simulated sea-ice conditions from the (climatological) specification of the surface boundary conditions in the atmospheric general circulation model (AGCM), the sea-ice model is coupled additionally to a one-dimensional atmospheric boundary layer model. Using the global ECMWF-analyses as before, the coupled model is now forced from the geostrophic level (850 hPa). Without any changes of the original model parameters and physics, the results are rather poor in that the ice extent as well as the ice velocities are generally too low and that the ice thickness distribution resembles the results of a pure thermodynamic sea-ice model. The results with the forcing from the higher level are more realistic when snow and mixed-layer effects are neglected, thus resembling those of Koch (1988) in the Weddell Sea. This indicates that the parameterizations in the atmospheric boundary layer model have to be readjusted in order to interact realistically with the snow-sea-ice-oceanic mixed-layer model. Additionally, it will be demonstrated that the pattern of the wind field, whether from the geostrophic or the surface level, has a significant influence on the sea-ice model results.
Interannual characteristics of an 80 km resolution diagnostic Arctic ice–ocean model
Authors: Ries John E. , Hibler William D.
Published: September 2017

Seasonal simulations with large-scale coupled ice–ocean models have reproduced many features of the ice and ocean circulation of the Arctic Ocean and the Greenland and Norwegian seas (e.g. Hibler and Bryan, 1987; Semtner, 1987). However, the crude resolution and high lateral eddy viscosity used by these models prevent the simulation of many of the smaller-scale seasonal features and tend to produce sluggish circulation. Similarly, the use of a single year’s atmospheric forcing prevents the simulation of features on an interannual time-scale. As an initial step towards addressing these issues, an 80 km diagnostic Arctic ice–ocean model is constructed and integrated over a three-year period using daily atmospheric forcing to drive the model. To examine the effect of topographic resolution and eddy viscosity on model results, similar simulations were performed with a 160 km-resolution model. The results of these simulations are compared with one another, with buoy drift in the Arctic Basin, and with observed ice-edge variations. The model results proved most sensitive to changes in horizontal resolution. The 80 km results provided a more realistic and robust circulation in most areas of the Arctic and improved the modelled ice edge in the Barents Sea, while also successfully simulating the interannual variation in the region. Although it performed better than the 160 km model, the 80 km model still produced too large an ice extent in the Greenland Sea. No significant improvement in the ice-edge prediction was observed by varying the lateral eddy viscosity. The results indicate that problems remain in the vertical resolution in shallow regions, in treating penetrative convection, and in the simulation of inflow into the Arctic Basin through the Fram Strait.
Sea-ice mechanical energy balance: nearshore Chukchi Sea, 1982
Authors: Pritchard Robert S.
Published: September 2017

The mechanical energy balance of sea ice provides information about ice dynamic behavior, driving forces and the constitutive law. The energy balance equation, formed as the product of ice velocity with the ice momentum balance equation, describes changes to the kinetic and potential energy densities as power is input to the ice by wind and current. The momentum balance equation may also be used to describe the ice-stress divergence, air stress, and water stress, but the scalar form of the energy balance is simpler to understand. This paper provides new interpretations of several terms in the energy balance equation, in particular power input by air and water stress and by sea-surface tilt. Barometric pressure fields and drifting buoys deployed on the Chukchi Sea ice cover during 1982 provide wind, ice motion and current measurements that allow each term in the energy balance equation to be evaluated as a function of time. Magnitudes of power input by wind and current show how the energy balance is decomposed and help describe the relative importance of these driving forces. In the nearshore Chukchi Sea during February, March and April 1982, both wind and current provided significant forcing of the ice. Ice stress was also important and, at times, dominated other terms in the mechanical energy balance.
The influence of humidity on the ablation of continental-type glaciers
Authors: Ohno Hiroyuki , Ohata Tetsuo , Higuchi Keiji
Published: September 2017

The annual evaporation of a continental-type glacier (43°05’ Ν, 86°48’ E) in the Chinese Tien Shan is estimated, based on data derived from four field observations carried out between summer 1987 and spring 1988, and data from a permanent weather station near the glacier. The evaporation during the melting and non-melting seasons is estimated as 81 mm and negligible, respectively. Assuming that the ablation is equivalent to the annual precipitation (650 mm) in 1987, estimated annual evaporation of 81 mm is 12% of the ablation and consumes 54% of the energy which causes the ablation. It can be said that evaporation suppresses ablation by 50% in comparison with the condition in which there is no evaporation.

The influence of fluctuations of air temperature and humidity on the ablation of the glacier were evaluated. Changes in temperature and humidity cause larger changes in ablation of glaciers in a cold and dry climate. The influence of humidity change is very important to glaciers located in a relatively warm environment.
Relation between recent glacier variations and climate in the Tien Shan mountains, central Asia
Authors: Chaohai Liu , Tianding Han
Published: September 2017

Since the Little Ice Age, most glaciers in the Tien Shan mountains have been retreating. Owing to an increase in precipitation in most parts of the mountains during the late 1950s to early 1970s, the percentage of receding glaciers and the speed of retreat have tended to decrease in the 1970s. However, the general trend of continuous glacier retreat remains unchanged, in part because the summer air temperature shows no tendency to decrease.

In the Tien Shan mountains, as the degree of climatic continentality increases the mass balance becomes more dependent on summer temperature, and accumulation and ablation tend to be lower. Therefore, the responses of glaciers to climatic fluctuations in more continental areas are not synchronous with those in less continental areas, and the amplitude of the glacier variations becomes smaller.
Investigation of glacier bursts of the Yarkant River in Xinjiang, China
Authors: Xiangsong Zhang
Published: September 2017

The jökulhlaups in the Yarkant (Yarkand) River are usually caused by the sudden drainage of glacier-dammed lakes through rapidly expanding subglacial channels. The lakes are dammed by Keyajir (Kyagar) Glacier and Telamukanli (Singye) Glacier which are situated in the upper reaches of the Keleqin (Shaksgam) River. In recent years the glaciers have become thinner, and the glacier-dammed lakes and their outbursts have become smaller.
Identification of glaciers with surge characteristics on the Tibetan Plateau
Authors: Wenjing Zhang
Published: September 2017

Investigations of Zelunglung and Midui Glaciers in southeast Tibet, China, indicate that they have some characteristics of surge-type glaciers. There have been two extraordinary movements of Zelunglung Glacier, one in 1950 and one in 1968. A collapse of the terminus area took place in 1984. Midui Glacier experienced extraordinary movements about 55 years ago and also in 1988. During these events, the glacier termini reached moraines formed during neoglaciation and the Little Ice Age. The advances of the two glaciers are not related to climate variation. The glaciers caused serious disasters with loss of life and property, and disruption of transportation corridors.
Application of nonlinear colour enhancement on transparencies for interpretation of glacier surface characteristics
Authors: Meisheng Cao , Desheng Mi , Yinbin Pu , Jinghaung Liu
Published: September 2017

According to the analysis of grey scale range on MSS-4, -5, -6 and -7 channel image films for five snow-ice categories on glacier surface, the grey scale among snow, bare ice, ice pinnacle, moraine-covered ice surface and gully bed has been spread nonlinearly by using duplicative processing on high-contrast film. As a result of the rescaling of grey levels, the colour differences of morphological features of Rongbu Glacier in the Qpmolangma region have been increased on false colour composite photography. It is also shown that using MSS-6 to composite false colour images compared to MSS-5 will supply more information for the interpretation of the glacier area.
Satellite snow-cover monitoring for the prediction of snowmelt runoff in the upper reaches of the Yellow River, China
Authors: Qunzhu Zeng , Xuezhi Feng , Xianzhang Chen , Yongchao Lan , Jian Wang , Yujie Liu
Published: September 2017

Spatial-temporal variations in the extent of the seasonal snow cover of the upper reaches of the Yellow River were studied sytematically, using NOAA, Landsat, MSS and TM images, supported by ground-truth data. Effects of changing areal extent of snow cover on river flow were also examined. Spring-runoff forecasting models were developed, based on ridge regression methods and Grey theory, employing satellite snow-cover and actual hydrometeorological data to forecast inflow to the Longyang Gorge reservoir for ten-day periods between April and early June. Forecast precision is within ±15% of the actual observation. Separating snow-cover data by elevation zone improves the accuracy of forecast over lumping snow cover over the entire basin.
Differences in mass-balance calculations resulting from alternative sampling and estimation techniques on Glacier No. 1, Tien Shan, China
Authors: Elder Kelly , Kattelmann Richard , Ushnurtsev Sergei N. , Daqing Yang , Chichagov Alexander
Published: September 2017

In May of 1990, three research groups from China, the Soviet Union and the United States visited Glacier No. 1 in the Ürümqi river basin, Xinjiang Uygur Autonomous Region, northwestern China, in a cooperative effort to examine differences in mass-balance calculations resulting from sampling and estimation procedures. Three different snow-depth data sets were collected consisting of: (1) high-resolution depth transects covering the glacier, (2) depths taken from the permanent stake network, and (3) an intermediate data set constructed using the stake network and supplementary depth data from locations not covered by the stake network. The glacier was divided into ten elevation zones and the data were registered to a digital elevation model for analysis. Results show that the permanent stake network provides an accurate estimate of total mass balance if certain techniques are used for extrapolation to higher elevations, although estimates of mass balance for particular regions of the glacier are not accurate. Some regions were overestimated while others were underestimated, leading to a good overall estimate. The intermediate-resolution data set provided better within-zone estimates of mass balance, but was less accurate than the stake network for total mass balance.
The movement mechanisms of Ürümqi Glacier No. 1, Tien Shan mountains, China
Authors: Maohuan Huang
Published: September 2017

Beneath Ürümqi Glacier Νo. 1, there is an ice-laden till layer which is more than 10 m thick near the terminus. The 0°C isotherm is generally at some depth below the glacier sole and lies within the bedrock below the ice-laden till layer near the terminus. Thus the glacier is entirely cold and impermeable, except for a thin snow-firn layer at its surface and some crevassed areas. Meltwater drains off mainly by surface channels, assisted by subglacial conduits. Four flow mechanisms have been identified in the glacier. They are ice deformation, bed deformation, shear faulting, and sliding over the bed. At the terminus and along the margins, bed deformation can provide a significant contribution to the overall surface motion. Bed deformation consists of creep and discontinuous slip. However, creep experiments on samples taken from the ice-laden till layer provide no positive indication that this layer deforms more easily than clean ice. Discontinuous slip thus may provide the major contribution to bed deformation.
Some glacio-micrometeorological features on the north side of Mount Qogir (K2), Karakoram mountains
Authors: Yongjian Ding
Published: September 2017

Measurement of wind velocity, wind direction, air temperature, precipitation and humidity were obtained at various altitudes in order to describe micrometeorological conditions on the north slope of Mount Qogir (K2). Meteorological elements were monitored above the moraine surface in the proglacial area and over the ice surface in the ablation area and snow surface in the firn area of K2 glacier. Precipitation increases quickly with altitude from the dry valley to the firn area. Relative humidity also increases with elevation. In the K2 glacier area, the highest absolute humidity occurs over the glacier tongue. The effects of melting and freezing of the surface of the glacier in the ablation area on diurnal and day-to-day changes in air temperature influence air temperature in ablation areas, decreasing diurnal range by comparison with the firn areas. On clear days, a down-valley wind blows from the firn area before sunrise and an up-valley wind after sunrise. On days with precipitation, an up-valley wind predominates in the night-time and a down-valley wind in the day-time.
Predictions of changes of glacier mass balance in the Nepal Himalaya and Tibetan Plateau: a case study of air temperature increase for three glaciers
Authors: Ageta Yutaka , Kadota Tsutomu
Published: September 2017

Annual mass exchange differs between maritime and continental glaciers. A common characteristic of these glaciers in Asian high-mountain areas is that most of the annual accumulation occurs in summer. Since variations in mass balance of a summer-accumulation type of glacier are quite sensitive to variations in summer air temperature, shrinkages of such glaciers due to climate warming are predicted by the use of simplified experimental relations between air temperature and mass balance, disregarding variation of other climatic variables such as cloudiness and precipitation. The results predict that both small and large maritime glaciers are more sensitive to warming than a continental ice cap. A small glacier would disappear in a few decades if the air temperature persisted a few degrees above that of an equilibrium state of mass balance.
Climatic influence on the composition of snow cover at Austre Okstindbreen, Norway, 1989 and 1990
Authors: Yuanqing He , Theakstone Wilfred H.
Published: September 2017

Winter snow cover at Austre Okstindbreen is influenced strongly by patterns of atmospheric circulation, and by air temperatures during precipitation. Differences of circulation over the North Atlantic and Scandinavia during the winters of 1988–89 and 1989–90 were reflected in the ionic and isotopic composition of snow that accumulated at the glacier. Early summer ablation did not remove, or smooth out, all the initial stratigraphic differences. In the first half of the 1988–89 winter, most air masses took a relatively short route between a marine source and Okstindan; late winter snowfalls were from air masses which had taken a longer continental route. The snow that accumulated in the first half of the 1989–90 winter was associated with air masses which had followed longer continental routes, and so brought higher concentrations of impurities from forests, lakes and crustal material. The ablation season began earlier in 1990 than in 1989, and summer winds and rain supplied more impurities to the snowpack surface.
Finite ice failure depth in penetration of a vertical indentor into an ice edge
Authors: Kärnä Tuomo
Published: September 2017

This paper presents a partial analysis of data from an extensive series of laboratory indentation tests. The tests were conducted using flat indentors pushing against sheets of fresh-water ice of thickness 65 to 115 mm. The aspect ratio ranged from 0.9 to 2.6 with indentor velocities of 10 to 80 mm s−1. Details of an ice failure mode known as “crushing with flaking” are studied by making use of measured force-displacement signals and high-speed photography. With these test conditions, ice failure is associated with a production of symmetrical flakes which emanate simultaneously up and down. The failure begins in the middle level of the ice sheet as a rapid expansion of the ice. The post-peak phase of the ice failure involves loss ol the ice material over the whole contact area. The amount of ice that is extruded after the occurrence of the peak force is characterized by a finite failure depth parameter. According to present data, this failure depth is around 70% of the total depth of crushing and flaking that occur during a cycle of loading and unloading.
Investigations of discrepancies between laboratory studies of the flow of ice: density, sample shape and size, and grain-size
Authors: Jacka T. H.
Published: September 2017

Laboratory results are presented concerning ice creep at minimum creep rate (at ~1% strain) for fine-grained, initially isotropic, polycrystalline samples. The effect on the creep rate of ice density, sample shape (aspect ratio) and size, grain-size and ratio of grain-size to sample size is examined. Provided sample density is above ~0.83 Mg m−3 (i.e. the close-off density), there is no effect of density on ice-creep rate. Results provide no evidence of a creep rate dependence on test sample length for cylindrical samples. Sample diameter, however, does affect creep rate. Over the range of sample diameters studied (16.2 to 90 mm) creep rate decreases monotonically by a factor of ~4. This effect is independent of sample aspect ratio. Experiments examining size effects in simple shear indicate no dependence of minimum flow rate on shape or size in this stress configuration. Two grain-sizes were represented within the samples tested for the effect of sample size. As expected from earlier work, no grain-size effect on minimum creep rate is evident. In addition, there was no evidence of an effect on creep rate of the ratio of grain-size to sample size.
Application of a new friction theory to ice and snow
Authors: Makkonen Lasse
Published: September 2017

A new theory, in which friction is interpreted as the energy flux required to form surface at contact asperities, is applied to sliding on ice and snow. The results of this theoretical investigation show that in dry friction the relevant contact areas are of almost molecular scale. The properties of the interface layer in ice and snow friction arc poorly known, so that the implications of this new theory are somewhat speculative. However, qualitative agreement with experimental data is good, and the theory provides explanations to the success of some empirically developed methods of improving the frictional properties of skis and sledges.
Friction of melting ice
Authors: Jones Stephen J. , Kitagawa H. , Izumiyama K. , Shimoda H.
Published: September 2017

The friction of pure ice against various materials was studied at the melting point by pulling plates of the materials of known roughness under a melting ice sample, which was loaded from above, and by maintaining a surrounding air temperature of +2°C (±1°C). Speed was varied over a wide range from 0.05 to 400 mm s−1.

Results for an aluminium sheet of roughness Ra = 0.84 μm, showed a maximum in friction coefficient of 0.04 at a speed of 16 mm s−1. Below this speed the friction coefficient dropped to 0.002 at 0.2 mm s −1 and results from different ice samples were very reproducible. Above 16 mm s−1, the friction coefficient initially dropped to about 0.002 at 100 mm s−1, and then increased again to 0.037 at 400 mm s−1. Results at speeds above 16 mm s−1 were much less reproducible than those at lower speeds. Results are given also for the friction of ice on Formica, acrylic, and copper plates.

The amount of meltwater produced during a test was measured by weighing an absorbent tissue before and after mopping-up the meltwater. The amount of meltwater was significantly more for aluminium than for Formica or acrylic, showing that the thermal conductivity of the slider was controlling the amount of meltwater. The amount was also a strong function of velocity.
Isotopic and ionic changes in a snow cover at different altitudes: observations at Austre Okstindbreen in 1991
Authors: Raben Peter , Theakstone Wilfred H.
Published: September 2017

Ionic and isotopic analyses of snow samples collected at four sites at the Norwegian glacier Austre Okstindbreen during two field seasons in 1991 showed that, before melting started, the snowpack was vertically inhomogeneous. Patterns of variation with depth of both ions and oxygen isotopes were maintained throughout the pre-melt period. Horizontal variations of ionic concentration were smaller than vertical ones. The stratigraphic pattern of ionic concentrations in the pack at lower altitudes reflected the influence of melting-refreezing processes, as well as original variations in the falling snow. The mean ionic content of the first set of samples collected at the lowest site was much lower than that at the others, indicating that ions had already been removed by meltwater. Much liquid water was present in the snowpack when drainage started, and ions were removed quickly with the first meltwater. During the melting phase, comparative rates of loss of ions resulting from differential movement through the pack were SO42− > Na+ > Cl−. At 1475m, only 13% of the winter accumulation melted between 6 June and 9 July, but at least 88% of the Na+, 89% of the Cl− and about 100% of the SO42− was lost. Initially, there was no altitudinal trend in the mean δ18O values of the snowpack. Warming of the pack was accompanied by a tendency towards isotopic homogenisation. At the three sites at which snow remained in July, considerable 18O enrichment had occurred since the middle of June.
Glacial cirque formation in northern Scandinavia
Authors: Richardson Cecilia , Holmlund Per
Published: September 2017

Passglaciären is a small cirque glacier in the Kebnekaise massif, northern Sweden. It is frozen to its bed over more than 70% of its area, and under present climatic conditions has little effect on cirque formation. More favourable conditions for cirque glacier erosion during the Holocene are of short duration. Assuming similar conditions during previous interglacials, it is suggested that forms such as the Passglaciären cirque developed mainly during the initial phases of glacials when they were part of networks of large valley glaciers or of a small warm-based mountain-centred ice sheet. Passglaciären has been examined in order to evaluate its erosive capacity and its association with the subglacial cirque morphology. The methods used are radar surveys and direct ice-temperature measurements. Erosion is restricted to a small section of the glacier bed, at present resulting in only partial deepening of the cirque and erosion of the backwall. In cold, arid regions with extensive permafrost, small cirque glaciers are largely frozen to the bed, and therefore cannot contribute significantly to cirque formation. In such regions glacial erosion by larger temperate glaciers is more likely to be the major cause of cirque excavation.
Characteristics of basal ice at Engabreen, northern Norway
Authors: Jansson Peter , Kohler Jack , Pohjola Veijo A.
Published: September 2017

Subglacial intakes in a tunnel system underneath Engabreen, northern Norway, provide access to the underside of a 200 m thick glacier. Detailed observations and measurements were made in several ice tunnels melted out along the glacier bed. A 20–200 cm thick basal sediment layer is overlain by clean glacier ice. Stratigraphy is complex, with alternating sediment-rich and sediment-free layers, and pervasive shearing. Throughout the basal ice are numerous spheroidal water pockets, which increase in both size and degree of elongation with distance from the bed. Ice cores were retrieved from ice-tunnel walls for sediment, cation and isotope analysis. Our observations and measurements provide evidence for both accretion in and water movement through the basal ice. This supports the modification to classical regelation theory proposed recently by Lliboutry in which water flow in the vein network is required to achieve net accretion of regelation layers.
Preliminary results of tritium analyses in basal ice, Matanuska Glacier, Alaska, U.S.A.: evidence for subglacial ice accretion
Authors: Strasser Jeffrey C. , Lawson Daniel E. , Larson Grahame J. , Evenson Edward B. , Alley Richard B.
Published: September 2017

The stratified-facies ice of the basal zone of Matanuska Glacier, Alaska. U.S.A., contains significant concentrations of anthropogenic tritium, whereas unaltered englacial-zone ice is devoid of tritium. Supercooled water flowing through subglacial conduits during the melt season likewise contains tritium, as does frazil and other platy ice that nucleates and grows within this subglacially flowing water. These initial results demonstrate net accretion of more than 1.4 m of stratified basal-zone ice since initiation of above-ground, thermonuclear bomb testing in 1952. Furthermore, these results support a theory of basal ice formation by ice accretion and debris entrainment from supercooled water within a distributed subglacial drainage system.
Nature of basal debris in the GISP2 and Byrd ice cores and its relevance to bed processes
Authors: Gow Anthony J. , Meese Debra A.
Published: September 2017

Successful core-drilling to bedrock of both the Greenland and Antarctic ice sheets offers unique opportunities for examining processes acting at the bed. At Byrd Station, Antarctica, penetration of the bed was accompanied by upwelling of glacial meltwater into the drillhole. The nature and disposition of sediment in the 4.83 m thick debris-rich basal ice, together with stable-isotope and gas analyses of the enclosing ice, confirm that incorporation of the debris occurred simultaneously with periodic “freeze-on” of basal meltwater. Currently, the presence of substantial meltwater at the ice/rock interface likely precludes any erosive activity at the bed. At GISP2, Greenland, basal silly ice, 13.1 m thick, is currently frozen to the bed at −9° C. Limited studies of the silty ice at GISP 2, together with results of more comprehensive investigations obtained by GRIP researchers on basal ice at a companion site at Summit indicate that the sediment-bearing basal ice likely formed in the absence of an ice sheet and was therefore unrelated to direct interaction of the present ice sheet with its bed. The fact that the basal ice at Summit is frozen to the bottom also precludes any likelihood of erosive activity at the bed.
A laboratory study of sediment deformation: stress heterogeneity and grain-size evolution
Authors: Iverson Neal R. , Hooyer Thomas S. , Hooke Roger Leb.
Published: September 2017

In shearing sediment beneath glaciers, networks of grains may transiently support shear and normal stresses that are larger than spatial averages. Consistent with studies of fault-gouge genesis, we hypothesize that crushing of grains in such networks is responsible for surrounding larger grains with smaller grains. At sufficiently large strains, this should minimize stress heterogeneity, favor intergranular sliding and abrasion rather than crushing, and result in a self-similar grain-size distribution.

This hypothesis is tested with a ring-shear device that slowly shears a large annular sediment sample to high strains. Shearing and comminution of weak equigranular (2.0–3.3 mm) sediment resulted in a self-similar grain-size distribution with a fractal dimension that increased with shear strain toward a steady value of 2.85. This value is significantly larger than that of gouges produced purely by crushing, 2.6, but it is comparable to values for tilts thought to be deforming beneath modern glaciers, 2.8 to nearly 3.0. At low strains, under a steady mean normal stress of 84 kPa, variations in normal stress measured locally ranged in amplitude from 50 to 300 kPa with wavelengths that were 100 times larger than the initial grain diameter. Crushing of grains, observed through the transparent walls of the device, apparently caused the failure of grain networks. At shearing displacements ranging from 0.7 to 1.0 m, the amplitude of local stress fluctuations decreased abruptly. This change is attributed to fine sediment that distributed stresses more uniformly and caused grain networks to fail primarily by intergranular sliding rather than by crushing of grains. Sliding between grains apparently produced silt by abrasion and resulted in a fractal dimension that was higher than if there had been only crushing.

A size distribution with a fractal dimension greater than 2.6 is probably a necessary but not sufficient condition for determining whether a basal till has been highly deformed. Stress heterogeneity in subglacial sediment that is shearing through its full thickness should contribute to the erosion of underlying rock.
Is erosion by deforming subglacial sediments significant? (Toward till continuity)
Authors: Cuffey Kurt , Alley Richard B.
Published: September 2017

A glacier moving by deformation of subglacial sediments will tend to exhaust its own sediment supply, unless new sediment is generated subglacially. We explore the potential for deforming sediments to overcome this difficulty and replenish themselves by abrading their beds. We review abrasion experiments and theory for brittle materials and conclude that a theoretical calculation of abrasion is not possible yet. Instead, we use fault-gouge production data to estimate a likely upper bound to abrasion rates, and conclude that sufficient erosion to maintain a steady deforming-layer thickness is difficult to achieve, and will only be possible if the substrate is very soft and if there is a moderate rate of slip at the base of the deforming layer. Slow abrasion, which can leave a geologic signature, is possible under most deforming layers that are deforming at the sediment/bedrock interface.
Changes in the character of glaciomarine sedimentation in the southwestern Weddell Sea, Antarctica: evidence from the core PS1423-2
Authors: Crawford Kevin , Kuhn Gerhard , Hambrey Michael J.
Published: September 2017

Investigations of the stratigraphy and facies within a 2.69 m long gravity core (PS1423–2) from the southwestern Weddell Sea, Antarctica, indicate a significant change in the character of glaciomarine sedimentation since grounded ice withdrew from the continental shelf. Based on visual description, X-radiography, clast shape, particle-size analysis, physical properties and geochemical data, the core used in this analysis comprises five distinct units, from top to bottom: (i) massive diamicton, (ii) weakly to well-stratified diamicton, (iii) millimetre-scale laminated muds, with little or on coarse-clastic input, (iv) well- to weakly stratified diamicton, (v) massive diamicton. This succession is attributed to the variation in sedimentation associated with the recession of the grounding line of a previously advanced glacier. Grounded ice decoupled from the continental shelf to form an ice shelf, probably initiated by a rise in sea level in response to global climatic changes. Following disintegration of the ice shelf, sedimentation was influenced by marked variations in iceberg production. AMS-derived 14C ages from the upper 46 cm of the core indicate that the succession has been deposited since the end of the most recent glacial maximum (late Pleistocene), a conclusion supported by published data.
Observations of the grounding-line area at a floating glacier terminus
Authors: Powell Ross D. , Dawber Michael , McInnes James N. , Pyne Alex R.
Published: September 2017

A robotic submarine was used for the first observations of a grounding-line area of a floating glacier. The site was Mackay Glacier which terminates as a floating glacier tongue in the Ross Sea, at latitude 77°S. Half of the 20 m thick basal debris layers in Mackay Glacier are deposited as subglacial till in the last 1.8 km that the glacier remains grounded. Subglacial till observed at and beyond the grounding line varies rapidly in texture and rheology spatially, occurring as a flat sheet, as flow-parallel flutes, or as bank forms into which it has been pushed at the grounding line. Very little free- flowing subglacial water was present during the observations, and no major subglacial water discharges appear to have occurred in the past. The other half of the basal debris is melted out up to 1.5 km in front of the grounding line, producing a sheet of glacimarine sediment as shelfstone diamicton and mud draped on subglacial till. Both till and glacimarine sediment may be turbated by icebergs. This simple model of till overlain by shelfstone diamicton and mud is a direct contrast to sedimentary depositional systems at tide-water termini of temperate glaciers.
Cavities and the effective pressure between abrading clasts and the bedrock
Authors: Hindmarsh R. C. A.
Published: September 2017

The mechanical configuration of cavities associated with clasts is discussed, and how this affects the water pressure underneath the clast. The range of permissible water pressure is determined by flow parallel to the bed rather than by flow towards the bed. The actual pressure is controlled by hydraulic connections to areas away from the clast. The degree of cavitation provides an additional degree of freedom which adjusts to ensure that horizontal and vertical forces respect the Coulomb friction condition.
Sliding of till over bedrock: scratching, polishing, comminution and kinematic-wave theory
Authors: Hindmarsh R.C.A.
Published: September 2017

The observed ratio of removal of material by (i) scratches gouged by large clasts and (ii) polishing by debris suggests that the latter is the dominant form of bedrock erosion. We examine this with a multi-stage breakdown model of glacial debris, which includes active erosion by fines. These models suggest that a mother clast can, through the action of its daughter debris, erode several times its own volume of bedrock.

Till-sliding over bedrock is likely to be a potent source of scouring. By proposing a till/bedrock sliding law, we investigate the kinematics of sliding till bodies. Ice flow naturally tends to thin and extend till cover, even in the absence of longitudinal gradients in the applied stress. Thicker till cover has an increased effective pressure at its base, a lower sliding velocity and, for larger thicknesses, a decrease in sediment flux with thickness. This implies backward-moving kinematic waves and shocks. It is suggested that this is related to the blunt upstream faces of drumlins, and that drumlinization can be a consequence of debris sliding over bedrock.
Formation of thrust-block moraines at the margins of dry-based glaciers, south Victoria Land, Antarctica
Authors: Fitzsimons Sean J.
Published: September 2017

Several dry-based alpine glaciers in the Dry Valleys of south Victoria Land, Antarctica, have prominent end moraines. Examination of their morphology, structure and sedimentology shows they consist of blocks of sand, gravel and organic silt within which sedimentary structures unrelated to entrainment and transportation by ice are well preserved. The nature and preservation of sedimentary structures, together with the presence of algae mats in the sediment, suggest formation by proglacial entrainment, transportation and deposition of frozen blocks of lacustrine sediment. Previous explanations of the formation of thrust-block moraines, including those that stress the importance of elevated pore-water pressure and Weertman’s ice-debris accretion hypothesis, depend on the presence of subglacial meltwater or the 0° C isotherm being situated close to the glacier bed. These models appear inappropriate for cold, dry-based glaciers because their basal temperatures are well below freezing point and they rest on deep permafrost. Three alternative models for the formation of thrust-block moraines at the margins of dry-based glaciers are examined in this paper: block entrainment of sediment associated with frozen-bed deformation; entrainment by overriding and accretion of marginal-ice and debris aprons; and transient wet-based conditions associated with glaciers flowing into ice-marginal lakes.
Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada
Authors: Brennand T. A. , Shaw J. , Sharpe D. R.
Published: September 2017

Glaciofluvial ridges, several hundred kilometres long, are commonly referred to as interlobate moraines because they appear to have formed at the convergence of two distinct ice lobes. Flow convergence is indicated by patterns of striations, streamlined forms and eskers. The so-called interlobate moraines are also thought to have formed asynchronously as the ice margin retreated. By contrast, we argue that the Harricana moraine of northern Quebec, Canada, formed following flow convergence in a regional-scale subglacial outburst flood. Flowlines constructed from streamlined bedforms mapped on the glacial map of Canada, reinterpretation of these streamlined forms as products of meltwater erosion, and field records of erosional marks (S-forms) in bedrock and glaciofluvial deposits to the lee of bedrock highs support this model. The effects of this flow convergence on the ice-sheet topography and drainage controlled the location of the broad conduit in which the Harricana moraine was deposited. Continued flow in this conduit and melting of the conduit walls explain the local patterns of striae, the supply of debris to the conduit, and the morphological and sedimentary characteristics of the moraine itself. From these characteristics, we conclude that the moraine was formed synchronously. This conclusion, if correct, is instructive regarding the deglacial hydrological organization of a large sector of the Laurentide ice sheet.
Abraded rock landforms (whalebacks) developed under ice streams in mountain areas
Authors: Evans Ian S.
Published: September 2017

Like many mountain ranges, the Coast Mountains of British Columbia, Canada, have undergone both local and ice-sheet glaciation. Effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice. The major valleys are broad glacial troughs with frequent rock basins. Their slopes are broken into rounded, steep-sided bosses whalebacks abraded on all sides: they are of the order of 100 m to 1 km long, and 10 m high. In the southern Coast Mountains, the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1.0–2.1 km thick, within the Cordilleran ice sheet. They are best developed where geological structures parallel the valley and thus the former ice-flow direction, but they are found on a range of lithologies and some are transverse to structure. The whalebacks provide an impression of glacial streamlining, and occasionally grade into rock drumlins. Roches moutonnées are rare in the major troughs.

It is hypothesised that these whalebacks and rock drumlins develop under ice streams of Greenland or East Antarctic type, sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features. Lee slopes are abraded when thick ice suppresses bed separation, even with rapid flow; basal ice of low viscosity would aid this suppression. Water pressures under the ice streams may have remained high, so that lee-side plucking was rare; such plucking is most likely where pressure fluctuates dramatically, and especially when lee cavities under active ice reach atmospheric pressure.