bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subglacial Regelation Water Film
Authors: Hallet Bernard 
Published: September 2017

AbstractRecent studies of subglacially precipitated carbonate deposits and associated solutional furrows have provided interesting new insight on subglacial water films, as well as on chemical exchange at the glacier bed. Considerable information on the film thickness and its temporal and spatial variability has been gained by analyzing several properties of subglacial carbonate deposits including: (1) the morphology of surface features aligned parallel to ice flow, (2) the laminated structure, and (3) the size distribution of fine rock fragments presumably transported in the film prior to their incorporation in the deposits. Chemical analyses of water from pro-glacial streams, together with calculations of CaCO3 solubility and mass balance, show that the channelized water is chemically distinct from the film water in which CaCO3 precipitates, and that subglacial precipitation is not possible where there is a considerable water flux through the film in excess of that associated with regelation sliding. The principal implication of these studies is that a temperate cirque glacier is characteristically separated from its bed by a thin water film, probably micrometers in thickness; however, the film appears to occasionally thicken, at least locally by as much as a hundred fold in exceptional cases. Furthermore, the water flux and/or solute concentration in the basal film undergoes periodic, probably seasonal, variations possibly related to variations in the amount of water reaching and flowing through the basal film.
Variations in Time and Space of the Velocity of Lower Columbia Glacier, Alaska
Authors: Meier Mark F. 
Published: September 2017

AbstractIce velocity, acceleration, and strain-rate are being measured at intervals of about 45 d using automated processing of aerial photographs. Preliminary results for the lowest 6 km of Columbia Glacier for the period July 1976 to November 1977 show the following:
(1)High rates of flow (2–6 m/d) and longitudinal extension (occasionally exceeding 1/a).(2)A smooth, almost sinusoidal change in velocity 6 km above the terminus from about 2 m/d in August 1976 and 1977 to about 3 m/d in February–March 1977.(3)Very rapid increases in velocity near the terminus in October 1976 and September–October 1977 which follow embayment formation (increased iceberg calving).(4)A suggestion that the rapid velocity increases propagate up-glacier for 3–4 km before becoming unrecognizable.(5)Seasonal changes in velocity (which presumably relate to basal sliding) ranging from about 1 m/d 6 km above the terminus to about 4 m/d near the terminus.
Observations Of Glacier Seismicity On Unteraargletscher
Authors: Deichmann N. , Ansorge J. , Röthlisberger H. 
Published: September 2017

AbstractAlmost continuous recordings of glacier seismicity were obtained on Unteraar-gletscher (Berner Oberland, Switzerland) over a period of two weeks at the end of May 1977. The seismograph array consisted of micro-earthquake recorders, some recording directly onto smoked paper (three Sprengnether model MEQ-800) and others recording onto magnetic tape (one MARS-72 apparatus and two seismic-event recorders). The frequency range covered by the instruments lies between 1 and 85 Hz. The array spanned a relatively crevasse-free area of about 500 m by 700 m.At the beginning of the period of observation only a few events were recorded per hour. Probably as a consequence of increased run-off of melt and rain, which acted as a lubricant or as an agent of hydraulic fracturing within or beneath the glacier, the activity rose in two days to a maximum of 120 events in one hour, and then with minor fluctuations it gradually decreased again to its initial level. The variations in activity showed signs of correlating with the velocity measurements, which however were only started after the main maximum, but did not seem to be influenced by the uplift of the glacier surface or by the diurnal meteorological fluctuations.Most of the recorded signals could be classified according to their frequency content into three groups: 40, 20, and 5 Hz. The 40 Hz events, whose duration was less than 1 s, are located near the glacier surface and probably correspond to those attributed by Neave and Savage (1970) to the formation of crevasses. The majority of the events were of the 20 Hz type, each of about 1 s duration. Due to inadequacies in the seismometer array, only three of them could be located with sufficient accuracy: they originated in different areas of the glacier at a depth of about 150 m, which is strong evidence that icequakes are not, as previously thought, limited to the upper 40 m. The signals of the 5 Hz type, lasting several seconds, are thought to be 20 Hz events whose higher frequencies have been attenuated by a longer travel path. The lower-frequency signals from the glacier bed, reported by Bindschadler (unpublished) and by Weaver and Malone (1979), were not observed. This could indicate that a variety of mechanisms are operative at different times of year. In particular, the subglacial conduits were only poorly developed in Unteraargletscher at the time of these recordings.
Importance of Plastic Deformation in Regelation of Ice
Authors: Tusima K. , Tozuka S. 
Published: September 2017

AbstractIt is well known that regelation may occur by pressure-melting in front of a wire and refreezing at the rear. The velocity of the wire has been observed to have values ranging from 10–5 to 10–1 mm/s. However, there have always been large discrepancies between experiments and any theory based on this mechanism, and, when moving at a comparable velocity, hard balls slid on an ice surface leave grooves made by plastic deformation. So, we conducted experiments to test whether regelation phenomena might be explained by plastic deformation of ice around the wire.
Transient Water Flow in Subglacial Channels
Authors: St Lawrence William , Qamar Anthony 
Published: September 2017

AbstractA hydraulic mechanism is postulated as the source of certain low-frequency (1-5 Hz) seismic signals that are recorded in the vicinity of temperate glaciers. To illustrate that the mechanism is a plausible seismic source, the equations of motion and continuity for transient flow in a subglacial conduit are developed. The solution to these equations is obtained for the case of the flow of water being terminated in a glacial conduit. Using reasonable values of physical parameters taken from the literature, the displacement of the conduit walls is determined as a function of time and distance along the tunnel. The spectral character of the proposed source and the period of time over which it operates is compared with seismic records of typical type II signals. The agreement in terms of these parameters is good.To further examine the validity of the proposed seismic source a preliminary energy calculation is made which demonstrates that the proposed mechanism is energetically reasonable. Evidence of hydraulically generated seismic waves from a dam site is introduced to support the theory of a hydraulic source.Based on the evidence presented, it is suggested that the flow of water from glaciers is modulated by an internal flow regime that is intermittent in time and space.The substance of this paper is included in a report by the present authors entitled “Hydraulic transients: a seismic source in volcanoes and glaciers”, published in Science, Vol. 203, No. 4381, 1979, p. 654–56.
The Distribution of 10m Temperatures on the Ross Ice Shelf
Authors: Thomas R.H. 
Published: September 2017

AbstractTen-meter temperatures on the Ross Ice Shelf increased by I deg between 1958 and 1974. Surface temperatures at the “Byrd” and McMurdo stations have also risen during this period and the observed change is consistent with the 10m temperature increase. This rising trend in temperature appears to have an anti-phase relationship with northern hemisphere cooling.
On the Thermal Regime of a High-Arctic Valley Glacier
Authors: Müller Fritz 
Published: September 2017

AbstractThe 10 m temperatures were measured over several years at 16 sites on the White Glacier (lat. 80° N.), Axel Heiberg Island, Canadian Arctic Archipelago. At three sites deep profiles were made using a new drilling technique, reaching a maximum depth of 280 m. Large differences in the 10 m temperatures between locations and from year to year were observed. The deviations of these temperatures from the almost isothermal mean annual air temperature over the glacier are discussed. The heating effect of the melt water in the lower percolation zone was found to be very important. A conceptual model is developed to assess the influence of these irregularities in the energy input at the upper boundary on the thermal regime of the entire glacier. So far a quantitative analysis has been made only for the relatively simple 30 m temperature profile measured on the tongue of the glacier.
Impurities and their Distribution in Temperate Glacier Ice
Authors: Harrison W.D. , Raymond C.F. 
Published: September 2017

AbstractTotal impurity content of salt plus carbon dioxide was estimated as a function of grain size and depth in polycrystalline ice samples cored from a temperate glacier by measuring the electrical conductivity of the melt with air excluded. Conductivity decreased with increasing depth and grain size and ranged from × 10-5 to 0.4 × 10-5 Ω -1 m-1 at 0°C. The conductivity of pure water at 0°C is 0.1 × 10-5 Ω -1 m-1 Studies of the configuration of the three phases and of in situ temperature were also made. Thermodynamic constraints indicate that these impurities are probably concentrated as follows: about 5 mol m-3 in the liquid in the veins along three-grain intersections, roughly 1 × 10-6 mol m-2 associated with grain-boundary area exclusive of veins, and about 0.7 × 10-3 mol m-3 in volume exclusive of veins and grain boundaries. The last of these categories seems to account for most of the impurities in coarse ice (grain size about 20 mm), but all three categories seem significant in fine ice (grain size about 2 mm). Differences in bulk impurity content possibly indicate different histories of flushing by water.
Abstracts of Papers Accepted for the Symposium but not Presented Mathematical Models of Ice Shelves
Authors: Shumskiy P.A. , Krass M.S. 
Published: September 2017

AbstractThe flat form and high ice velocity of floating glaciers are explained by the absence of shear stresses at the lower surface. In orthogonal co-ordinates with one axis normal to the upper and lower surfaces shear stresses in these glaciers are absent. Another important peculiarity of ice shelves is their essential non-isothermality. Among them two dynamically different types are distinguished, which are described by different models.A. External ice shelves join the coast at one edge and at some distance from it can expand freely in all directions. They can be considered with sufficient accuracy as flat plates without any physical differences between the directions of the horizontal plane, except that strains lead to the movement relative to the fixed edge. Thus the problem of thermodynamics becomes one-dimensional. In the affine dimensionless system of co-ordinates, the equations of the dynamics are simplified and together with the rheological equation lead to the non-linear integro-differential equation involving the reduced temperature. For the quasi-steady case, the boundary problem for this equation is solved by means of the method of sewing together of asymptotic expansions. It is shown that the stability of the thermodynamic regime in external ice shelves takes place only when the stream lines pass through both glacier surfaces, because in this case the advection removes the dissipative heat. In the case of ice coming from the upper and lower surfaces in opposite directions, the regime is unsteady because of the internal accumulation of heat.B. Internal ice shelves are limited by coasts from various sides and interact with them dynamically. In the boundary zone coasts provide a braking action and outside it they prevent sideways spreading. The relation between horizontal stresses is conditioned by the configuration of coasts, therefore the angle between the coasts, or between the directions of ice flow from them, is included essentially into the equations of thermodynamics. Another complication is connected with the considerable change of the temperature and of the accumulation- ablation rate at the upper and lower surfaces of the glacier along flow lines. Integro-differential equation for the temperature in this case is more complicated, but its solution is analogous to the case above. In the coastal zone the thermodynamics are described by other equations in connection with the predominance of the shear stress in the plane parallel to the coast.
Temperature Distribution in a Sub-Isothermal Glacier
Authors: Krass M.S. 
Published: September 2017

AbstractIn sub-isothermal glaciers heat conduction plays the main role in the formation of the temperature field, and the contribution of advection is relatively small. The dependence of the strain-rate on the temperature is simplified by a linear approximation. If the whole range of the temperature change in a glacier does not exceed ≈ 3 deg, with the power rheological law the quasi-steady temperature distribution is described by a simple analytical dependence. In the upper part of the ice, the temperature varies with depth almost linearly; the deflection from the linear distribution is essentially in the lower part.
Relaxation Self-Oscillations and Processes at the Bottom of Glaciers
Authors: Shumskiy P.A. 
Published: September 2017

AbstractIn terms of the theory of oscillations, rapid glacier advances (glacier surges) are relaxation self-oscillation, and large glacier advances of the same character dependent on climate are the result of interaction between forced and self-exciting oscillations.The relation is found between average shear stress and sliding velocity of pure and of moraine-containing ice along the bottom, taking into account the real thermal and kinematic boundary conditions, the different dependence of the ice melting point on hydrostatic pressureand on normal component of the stress deviator, and dry friction against the bottom. In the regime of bottom melting, a communicating system of subglacial drainage channels is formed along (he borders of distal slopes of bottom irregularities. Variations of effective roughness lead to the forced variations of sliding velocity depending on the surface melting rate.Relaxation self-oscillations of glaciers are caused by the alternation of “sticking” to the bottom in the phase of restoration and of rapid sliding along the bottom in the phase of relaxation because of the changes in the concentration of moraine material in the bottom layer of ice and of the force of dry friction against the bottom of a glacier.
Configurational Statistics
Authors: Nagle J. F. 
Published: September 2017

AbstractTheories of the dielectric constant in ice differ in three fundamentally different ways that are often confused with each other. First, there is the choice of interactions to include in the model, notably whether to try to include long-range dipolar interactions as in the Kirkwood theory or to include only the short-range ice-rule interactions. Second, there is the choice of the kind of statistical quantity calculated, e.g. the Kirkwood correlation factor g or the polarization factor G, which Stillinger and Cotter showed to be different. Finally, there is the choice of the kind of computational tool used, and in original papers this choice often obscures the first two differences. With these distinctions in mind a review is given of current theoretical calculations of the dielectric constant and the residual entropy and how the different theories relate to each other and to experiments.
Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection
Authors: Jezek Kenneth C. , Clough John W. , Bentley Charles R. , Shabtaie Sion 
Published: September 2017

AbstractValues of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.
Deformation of Ice Single Crystals Close to the Melting Point
Authors: Jones Stephen J. , Brunet Jean-Guy 
Published: September 2017

AbstractConstant strain-rate compression tests on ice single crystals at temperatures between –20°C and -0.2°C are described. The power-law dependence of yield stress on strain-rate gives a value of n which varies from 1.95±0.04 at –0.2°C to 2.07±0.08 at –20°C. The activation energy of deformation varies with strain-rate, but a mean value of 70±2 kJ mol–1 is obtained, with no indication of any increase close to maleting point,as has been found polycrystalline ice. An apparent work-hardening effect, at strains greater than 15%, is explained as being due to bending of the crystal changing the orientation of the basal planes.
Molecular Orbital Calculations of Water-Ice Surface Interactions
Authors: Plummer Patricia L. M. 
Published: September 2017

AbstractDetailed knowledge of the energetics of the interaction of a water monomer with an ice surface is important in understanding the factors which control both the nucleation and the growth of ice. In this work we model this interaction by using a small section of an ice surface and semi-empirical quantum-mechanical calculations of the CNDO/INDO type to investigate the energetics of a gas-phase molecule approaching the surface. In the attempt to simplify the system as much as possible while retaining the essential features of the "real" physical situation, 13 water molecules arranged in the lattice positions for ice Ih were used to represent the surface. Electron-density plots for both basal and prism surfaces were generated. Potential-energy curves were calculated for a monomer approaching a number of different sites on each type of surface. Monomer-surface binding energies varied from approximately 17 to 33 kJ/mol for the surface sites examined. Ion pairs of the H30+-OH- type were included in the surface and their effect on the energy of interaction with an incoming monomer calculated. For these studies no distortion of the ice surface was allowed. The energies found follow the same trends as observed for a free monomer-ion interaction.
Frazil Nucleation Mechanisms
Authors: Hanley Thomas O'D. 
Published: September 2017

AbstractPreviously the author had suggested that frazil nucleation occurs by a mechanism analogous to spinodal decomposition, aided by turbulence. After further study the following points are made: (1) No critical point exists between solid and liquid; this rules out true spinodal decomposition. (2) Pure water can be supercooled to -40°C; at -40°C the theoretical energy barrier to nucleation is about 10 -19 J. Frazil forms after supercooling less than 0.1 deg; at this temperature the theoretical energy barrier is about 10-14 J. (3) Theory shows that turbulence increases the energy barrier. (4) Turbulence may aid dissipation of heat of solidification, but not sufficiently to account for observed frazil formation at small supercoolings. (5) The author's evidence that frazil can begin to form at supercoolings as small as 0.02 deg suggests that no nucleus except ice itself can account for "heterogeneous" nucleation of frazil.
X-Ray Diffraction Topographic Observations of the Large-Angle Grain Boundary in Ice Under Deformation
Authors: Hondoh T. , Higashi A. 
Published: September 2017

AbstractLarge-angle tilt grain boundaries in artificially-grown ice bicrystals were observed by the method of X-ray diffraction topography. In bicrystals for which misorientation angles satisfy the conditions of a high-density coincidence site lattice (CSL) at the boundary, the images of fine parallel line defects appear on the topograph taken immediately after a light deformation. Since these images disappear in a time period between several hours and a few days and reappear again at the same sites when the specimen is deformed subsequently, it is concluded that these line defects are not stable like the boundary dislocations but may be steps generated on the boundary to form facets which coincide with the high-density CSL plane. X-ray topographic images of boundaries which do not satisfy the conditions of a high density CSL are complex and difficult to interpret, although some of the images indicate that there may be different types of structures on such boundaries.
Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature
Authors: Boned Christian , Lagourette Bernard , Clausse Marc 
Published: September 2017

AbstractDispersions of ice microcrystals were obtained from the breakdown of super-cooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4C1. Their complex permittivity ϵ* = ϵ′ - ϵ″ was studied versus their temperature T, up to the melting point of the ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680A) working at 400 Hz and 1 kHz. The plots ϵ′(T), ϵ″(T), and ϵ″(ϵ′) reveal that these systems exhibit two distinct dielectric relaxations located on both sides of a temperature Tm which was found to be equal to about —20°C in the case of water and lower than —20°C in the case of aqueous solutions of NH4C1. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice as T approaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice microcrystals, at discrete sub-zero temperatures close to their melting point.This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.