bluuebunny/crossref_metadata_2025_split huggingface dataset:
Airborne River-Ice Thickness Profiling with Helicopter-Borne UHF Short-Pulse Radar
Authors: Arcone Steven A , Delaney Allan J 
Published: September 2017

AbstractThe ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.
Environmental Constraints on West Antarctic Ice-Sheet Formation
Authors: Lindstrom D.R. , MacAyeal D.R. 
Published: September 2017

AbstractSmall perturbations in Antarctic environ-mental conditions can culminate in the demise of the Antarctic ice sheet’s western sector. This may have happened during the last interglacial period, and could recur within the next millennium due to atmospheric warming from trace gas and CO2increases. In this study, we investigate the importance of sea-level, accumulation rate, and ice influx from the East Antarctic ice sheet in the re-establishment of the West Antarctic ice sheet from a thin cover using a time-dependent numerical ice-shelf model. Our results show that a precursor to the West Antarctic ice sheet can form within 3000 years. Sea-level lowering caused by ice-sheet development in the Northern Hemisphere has the greatest environmental influence. Under favorable conditions, ice grounding occurs over all parts of the West Antarctic ice sheet except up-stream of Thwaites Glacier and in the Ross Sea region.
Calculation of Mass Balance of Glaciers by Remote-Sensing Imagery Using Similarity of Accumulation and Ablation Isoline Patterns
Authors: Krenke A.N , Menshutin V.M 
Published: September 2017

AbstractAn investigation of the combined heat, ice, and water balances was carried out in the Marukh glacier basin (west Caucasus) in 1966–67 to 1976–77, according to the International Hydrological Decade programme. Averaged glacier mass balance for these 11 years appears to be −55 g cm−2 year−1 according to stake measurements, and −51 g cm−2 year−1 according to geodetic measurements. The variability of accumulation is estimated as Cv = 0.15 and of ablation as Cv = 0.11. Thus, the variation in accumulation governs the oscillations in glacier balance. The inner nourishment of the glacier was also taken into account. The glacier mass balance is closely related to the relation between the accumulation and ablation areas. The “transient” values of both figures during the whole period of ablation can be used for this relation. The forms of the accumulation and ablation fields are similar from year to year and from one 10 day period to another. The areas of the accumulation and ablation zones are very different from one year to another. On the contrary, the average specific balance for each zone changes very little. One can use these features for the construction of accumulation, ablation, and specific mass-balance maps from satellite imagery. Mean values for the mass-balance terms occur in the vicinity of the equilibrium line. They can be calculated by using the air temperatures. Deviations from the means in different areas of the glacier determine the typical fields of the mass-balance terms.
Two-Dimensional Spreading and Thickening of Aufeis
Authors: Schohl G.A. , Ettema R. 
Published: September 2017

AbstractThe growth of two-dimensional, or laterally confined (flume), aufeis is shown from laboratory data to depend primarily on seven, independent, dimensionless parameters. During the early, two-dimensional, phase of its growth, aufeis consists of a mixture of ice and water, or ice-water slush, forming on a frigid base. Its early growth depends on four parameters: those expressing position along aufeis, period of spreading, slope of frigid base over which aufeis forms, and magnitude of heat flux to air from the surface of aufeis relative to latent heat release during freezing. The influences of two of the three remaining parameters, those expressing magnitude of heat flux to air relative to heat flux to frigid base and confined width of aufeis growth, are not felt until after a transition time has passed. The transition time apparently coincides with the beginning of the processes by which the ice-water slush on the surface of aufeis freezes solid. After a slush layer on aufeis begins to freeze solid, a new slush layer forms over its frozen surface. The continuing, cyclic process by which slush layers form and eventually freeze results in the ice laminations that are a feature of aufeis. The influence of the seventh governing parameter, a Reynolds number, cannot be discerned in the laboratory data.
BEPERS pilot study: an experiment with X-band synthetic aperture radar over Baltic Sea ice
Authors: Leppäranta Matti , Kuittinen Rlsto , Askne Jan 
Published: September 2017

AbstractRemote-sensing methods are the primary ones used for ice mapping in the Baltic Sea. A major methodological improvement is now being introduced by satellite radars due to their weather independency and high resolution. To learn how to use ERS-1 synthetic aperture radar (SAR) data, an extensive field programme BEPERS (Bothnian Experiment in Preparation for ERS-1) with airborne SARs has been arranged. The BEPERS pilot study was undertaken in 1987 using the French VARAN-S X-band SAR. The SAR was flown on 1 day over four study areas of size approximately 10 km x 50 km, and intensive validation observations were made. The data were most useful for the education they provided on how to work with SAR in sea-ice mapping. They have been used for developing SAR image-analysis methods, back-scatter modelling investigations and geophysical validation of SAR imagery. Cleaning-up of images consisted of speckle reduction and segmentation. Back-scatter characteristics of undeformed ice and ridges were examined. Ice-type classification was based on the box-classification method. Eight ice types were defined but basically only two types, undeformed ice/open water and deformed ice, could be discriminated. Two basic problems of high practical importance remained: how to discriminate between (1) open water and undeformed ice, and (2) ridged ice and brash ice. The data further showed illustrative examples of SAR imagery over sea ice.
Predicted time-scales for GISP2 and GRIP boreholes at Summit, Greenland
Authors: Schøtt Christine , Waddington E. D. , Raymond C. F. 
Published: September 2017

AbstractTwo deep-drilling projects (GISP2 and GRIP) in central Greenland will provide ice cores for paleoclimate studies. Drilling decisions and preliminary interpretations require age-depth curves (time-scales). Using a finite-element momentum-balance model, we calculate the modern ice-flow pattern on the flowline through the two drill sites. Our model appears to require relatively soft ice either throughout the ice sheet or below the Wisconsinan-Holocene transition in order to match the modern geometry and mass balance. By scaling the ice velocity to an assumed mass-balance history throughout the past 200 000 years, we estimate the time-scales at both sites. At GISP2, a flank site, we place the 10 000 years BP isochrone (representing the Wisconsinan-Holocene transition) at 1535 m ice-equivalent depth. At GRIP, on the ice divide, the corresponding depth is 1377 m. Our calculations show ice older than 200 000 years at 100 m above the bed at both coring sites. The time-scale calculation can be used for drilling decisions and preliminary interpretations. It should be refined as more regional-survey and ice-core data become available.
How can low-pressure channels and deforming tills coexist subglacially?
Authors: Alley Richard B. 
Published: September 2017

AbstractDeforming till and low-pressure water channels are observed to coexist subglacially, but till also is observed to creep rapidly into low-pressure subglacial regions. A simple model shows that these observations are not contradictory. Creep of a thin till to a low-pressure region can occur from a narrow zone only, and will lead to isolation of channels from till farther away.
Ice Fabrics in a Vertical Flow Plane, Barnes Ice Cap, Canada
Authors: Hooke Roger Leb. , Hudleston Peter J. 
Published: September 2017

AbstractAt a depth of about 75 m in the lower part of the accumulation area of the Barnes Ice Cap there is a change from fine-grained ice with a weakly-oriented c-axis fabric to coarser ice with a broad single-maximum fabric. At a depth of about 150 m the single maximum becomes elongate perpendicular to the direction of bubble elongation, and then splits into two distinct maxima making an angle of about 40–45° with respect to one another. At greater depths a third and finally a fourth maximum appear, forming the well known diamond pattern. Mean crystal size does not seem to increase in the transitions from one to two and thence to three maxima, but it may become more uniform. Crystal size does increase in the transition from three to four maxima, however. At the base of the glacier there is a 10–20 m thick layer of unusually-bubbly, fine-grained white ice with a strong single-maximum fabric.The depths to the transitions increase up-glacier and in place of the single-maximum fabric a small-circle pattern is found. Down-glacier the depths to the transitions decrease, systematically eliminating the higher zones. Thus in the lower part of the ablation area, ice with a four-maximum fabric appears at the surface.The independent variables governing these fabric transitions appear to be temperature T, stress τ, and cumulative strain ³oc. In a tentative stability diagram showing the fields in which given fabrics are stable in T–τ–³oc space, multiple-maximum fabrics occur at high temperatures (> —10°C) and at moderate to high stresses, weakly-oriented fabrics at low stresses or low cumulative strains, broad single-maximum fabrics at moderate stresses or moderate cumulative strains, and strong single-maximum fabrics at high stresses or large cumulative strains.
A Comparison between the Modern and Composite Pleistocene Snow-lines, Absaroka and Beartooth Mountains, Montana-wyoming, U.S.A.
Authors: Zwick Thomas T. 
Published: September 2017

AbstractThe modern and composite Pleistocene snow-lines of the Absaroka and Beartooth Mountains, Montana-Wyoming, were established from a population of 135 north-facing cirques and cirque glaciers distributed across Boulder River, Stillwater River, Rosebud, and Rock Creeks. The 3110 m elevation of the modern snow-line was established by connecting the accumulation-area ratios of 35 existing cirque glaciers. The composite Pleistocene snow-line was established by joining the mean floor elevations of the lowest abandoned cirques.Comparison of the modern and composite Pleistocene snow-lines indicates that the composite Pleistocene snow-line was depressed, at minimum, 305 m during the Pleistocene. The 305 m depression suggests that the mean Pleistocene temperatures were, at a minimum, 1.9 deg lower than the present mean annual temperatures found in the study area.Both the modern and Pleistocene snow-lines slope towards lower elevations in the Boulder and Stillwater drainages than in the Rosebud–Rock Creek drainages. Modern precipitation rates also show greater precipitation in the Boulder–Stillwater drainages than the Rosebud–Rock Creek drainages. The parallelism of the modern and composite Pleistocene snow-lines, and present precipitation rates suggest that temperature rather than precipitation is the controlling factor causing the depression of the snow-lines.The distribution of cirque elevations indicates that snow-lines fluctuated a minimum of four times during the Pleistocene.
Large Salt Beds on the Surface of the Ross Ice Shelf Near Black Island, Antarctica
Authors: Brady Howard Thomas , Batts Barry 
Published: September 2017

AbstractAn extensive system of mirabilite (Na2SO4 · 10H2O) beds has been mapped on the Ross Ice Shelf near Black Island. The salt beds are normally underlain by a thin layer of mud and their surface is covered by a non-marine algal mat and boulder lag. These authors suggest the salt has been formed by the displacement of sub-ice-shelf brines to the ice-shelf surface. Evidence also suggests that other terrestrial mirabilite beds in the McMurdo Sound area were formed in the same manner and deposited by the Ross Ice Shelf during its Wisconsin retreat from McMurdo Sound. Mirabilite salt in the dry valleys, southern Victoria Land, may have also originated from melt waters which dissolved ice-shelf mirabilite beds.
Variational Methods for Glacier Mechanics Problems
Authors: Oakberg Robert G. 
Published: September 2017

AbstractThe object of the research is to determine whether direct methods from the calculus of variations can provide convenient approximate solutions of complex problems in glacier mechanics. The Ritz technique is used to minimize an appropriate functional. Coordinate functions obtained from a finite-element model are combined with a coordinate function that is the solution of a related problem. The finite-element coordinate functions make localized adjustments to the related solution. Solutions of two sample problems are presented. An analysis of the closure of an intergranular vein in ice at the melting point is based upon a variational principle for velocities. An analysis of the flow of ice in a cylindrical channel is based upon a variational principle for stresses.
The Steady Profile of an Axisymmetric Ice Sheet
Authors: Johnson I. R. 
Published: September 2017

AbstractSteady plane flow under gravity of an axisymmetric ice sheet resting on a horizontal rigid bed, subject to surface accumulation and ablation, basal drainage, and basal sliding is treated according to a power law between shear traction and velocity. The surface accumulation is taken to depend on height, and the drainage and sliding coefficient also depend on the height of overlying ice. The ice is described as a general non-linearly viscous incompressible fluid, and temperature variation through the ice sheet is neglected. Illustrations are presented for Glen’s power law (including the special case of a Newtonian fluid), and the polynomial law of Colbeck and Evans. The analysis follows that of Morland and Johnson (1980) where the analogous problem for an ice sheet deforming under plane flow was considered. Comparisons are made between the two models and it is found that the effect of the third dimension is to reduce (or leave unchanged) the aspect ratio for the cases considered, although no general formula can be obtained. This reduction is seen to depend on both the surface accumulation and the sliding law.
Application of the Gravity Flow Theory to the Percolation of Melt Water Through Firn
Authors: Ambach W. , Blumthaler M. , Kirchlechner P. 
Published: September 2017

AbstractApplication of the gravity flow theory to the percolation of melt water through the firn in the accumulation area of a temperate glacier explains the occurrence of shock fronts in the melt-water flux. The time of propagation of a shock front moving from the surface through the entire firn was calculated under various assumptions. Various time input functions of melt-water flux at the surface with constant total input volumes yield only slight differences in the time of propagation of the shock front at greater depths. The dependence of the time of propagation of a shock front on the input volume, on snow parameters, and on the total thickness of the firn was calculated. An approximately linear relation was found to exist between the time of propagation of a shock front moving through the firn and the total thickness of the firn. The drainage of melt water from the firn after the summer ablation period is also quantitatively explained by the gravity flow theory. All results are in good agreement with experimental data.
Triaxial Testing of Frozen Sand
Authors: Parameswaran V. R. , Jones S. J. 
Published: September 2017

AbstractTriaxial testing of frozen saturated Ottawa sand under confined compression was carried out under hydrostatic pressures varying between 0.1 and 75 MPa at a temperature of -10°C and strain-rate 7.7×10-5s-1. Yield and failure stresses increased with increasing hydrostatic pressures up to about 40 MPa, beyond which the stresses dropped. The results are analysed according to the Mohr-Coulomb failure criterion and compared with past results in the literature.
An Active Rock Glacier, Wavbal Pass, Jammu and Kashmir Himalaya, India
Authors: Mayewski P. A. , Jeschke P. A. , Ahmad N. 
Published: September 2017

AbstractA currently active rock glacier with a snout elevation of 4055 m was observed in the Jammu and Kashmir Himalaya. Its formation is ascribed to stagnation of the terminal area of a true glacier.
First Glaciological Studies on the James Ross Island Ice Cap, Antarctic Peninsula
Authors: Aristarain A. J. , Delmas R. 
Published: September 2017

AbstractA 10 m deep core and a 2 m pit were achieved in December 1977 on the ice cap of James Ross Island (Antarctic Peninsula) 3 km westward of the main dome at an altitude of 1 500 m. The 10 m temperature was −14.2°C. The core was cut into 106 samples which have been used for density, total β radioactivity, electroconductivity, and deuterium-content measurements. The age at the bottom of the bore hole has been estimated to be 1 965±1 year and a mean annual snow accumulation rate 37.7±3.0 g cm−2 a−1 is calculated over the last 13 years. By comparing our results with those obtained in other areas of the Peninsula, the climate of the upper part of James Ross Island seems to follow the climatic regime of the western coast. A preliminary chemical analysis of the pit samples leads us to conclude that the snow impurities are mainly sea-salt derived. The conductivity measurements show a clearly defined peak at the end of 1967 which could be linked with the volcanic eruption of the Deception Island volcano in December 1967. The interest of the studied location is discussed in view of further more extended glaciological investigations and particularly a possible coring to the bottom.
On Glacier Energy Balance, Ablation, and Air Temperature
Authors: Braithwaite Roger J. 
Published: September 2017

AbstractThe paper tries to reconcile the facts that there are often useful correlations between ablation or run-off and air temperature while net radiation is usually the major source of ablation energy. Equations are derived from the energy balance to describe statistics for the ablation-temperature relation in terms of statistics for the relations between individual energy fluxes and air temperature. As examples, statistics are evaluated for four published series from Arctic Canada. Although the net radiation is the largest energy source in all four cases, the ablation rate is moderately well correlated with temperature and poorly correlated with net radiation. This is because the sensible heat flux is more variable than the radiation in three cases and is itself better correlated with temperature in all four cases. The major contributions to the increase of ablation rate with temperature (on average 6.3 kg m−2d−1deg−1) are due to sensible heat, followed by latent heat with a small contribution from net radiation. The resulting ablation-temperature model explains about half the variance of ablation rate. The main application of such a simple model is for the estimation of ablation totals in areas where glaciological and hydrological data are sparse.
Creep Slump in Glacier Reservoirs—Theory and Experiment
Authors: Shoemaker E. M. 
Published: September 2017

AbstractFrequently the reservoir region of a cold surge-type glacier has a temperate base, while in a region surrounding the reservoir the base is cold. We analyse the slump process in such a reservoir region— that is, the process whereby material flows toward the lower end of the region and forms a critical wave profile there. The model agrees qualitatively with observations of Trapridge Glacier, Yukon Territory, Canada, which is currently experiencing a critical pre-surge condition. Calculations based on the model give good agreement with the surge cycle time of Rusty Glacier, Yukon Territory. Laboratory experiments show that a large-amplitude slump-induced wave profile forms prior to a surge. Experimental surges were produced with velocity increases of order one hundred.
Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)
Authors: Smalley Ian J. 
Published: September 2017

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.
Ice Segregation as an Origin for Lenses of Non-Glacial Ice in “Ice-Cemented” Rock Glaciers
Authors: Wayne William J. 
Published: September 2017

AbstractIn order to flow with the gradients observed (10° to 15°) rock glaciers cannot be simply ice-cemented rock debris, but probably contain masses or lenses of debris-free ice. The nature and origin of the ice in rock glaciers that are in no way connected to ice glaciers has not been adequately explained. Rock glaciers and talus above them are permeable. Water from snow-melt and rain flows through the lower part of the debris on top of the bedrock floor. In the headward part of a rock glacier, where the total thickness is not great, if this groundwater flow is able to maintain water pressure against the base of an aggrading permafrost, segregation of ice lenses should take place. Ice segregation on a large scale would produce lenses of clear ice of sufficient size to permit the streams or lobes of rock debris to flow with gradients comparable to those of glaciers. It would also account for the substantial loss in volume that takes place when a rock glacier stabilizes and collapses.
Hoar-Crystal Method for Ice Fabrics
Authors: Shoji Hitoshi , Langway Chester C 
Published: September 2017

AbstractA new method has been developed for the observation of crystal axes orientation in fine-grained polycrystalline ice (grain-size approximately one millimetre). A two per cent ethylene dichloride solution of polyvinyl formal (Formvar) is applied to the surface of a sample. This solution produces adequate density of small holes in the Formvar coating and subsequently the nucleation sites for hoar crystal growth. The geometrical shape of each hoar crystal reveals both the c-axis and a-axes orientations using an optical microscope.