bluuebunny/crossref_metadata_2025_split huggingface dataset:
Explosive Growth of Shear-Heating Instabilities in the Down-Slope Creep of Ice Sheets
Authors: Yuen David A. , Saari Marc R. , Schubert Gerald 
Published: September 2017

AbstractThe time-scale for the onset of the explosive growth of a finite-amplitude shear-heating instability in the down-slope creep of a thick ice sheet is determined by integrating the equation for the temporal evolution of the temperature-depth profile subsequent to a sudden change in ice thickness. All instabilities eventually grow explosively after a prolonged period of simmering or relatively slow monotonic growth. Though times for explosive growth depend on initial and final ice thicknesses, surface temperature, accumulation rate, basal heat flux, and ice rheological parameters, the explosion times are extremely sensitive to the activation energy and the pre-exponential constant of the ice-creep law. Sudden increases in ice-sheet thickness of 1–2 km due to a rapid climatic deterioration can lead to explosive instability and melting of the basal shear layer in only thousands of years if ice-creep activation energies are lower than about 60 kJ mol-1.
Wave Ogives
Authors: Waddington E.D. 
Published: September 2017

AbstractWave ogives arise in a solution of the continuity equation by the method of characteristics. Steady ice flow is assumed. Ice velocity, channel width, and mass-balance functions combine to form a wave-excitation potential that yields the forcing function for wave ogives. This linear-systems formulation extends the ogive theory of Nye. Convolution of the temporal cumulative mass balance and spatial forcing functions gives the total wave pattern below an ice fall. Many ice falls do not generate ogives because the wave amplitude is modulated by a factor related to ice-fall length. The wave ogives at Austerdalsbreen, Norway, are due almost entirely to ice acceleration at the top of the ice-fall, i.e. the same zone that King and Lewis showed was responsible for forming Forbes bands.
Isotopic Fractionation at the Base of Polar and Sub-Polar Glaciers
Authors: Boulton G.S. , Spring U. 
Published: September 2017

AbstractThe melting of ice and the subsequent production of regelation ice from the melt water in a large-scale closed system beneath sub-polar and polar glaciers produces progressive fractionation between the melt water and the regelation ice derived from it. A theory is developed which predicts the change of isotopic composition in regelation ice in a subglacial zone of freezing and in the water from which it is derived. The theory is tested against data from the Byrd Station bore hole in West Antarctica, and applied to explain features of the isotopic composition in several other glaciers where thick sequences of regelation ice have formed.The principal conclusions are:1. Basal isotopic profiles can be used to reconstruct important features of a glacier’s hydrological system.2. Isotopic profiles in basal regelation ice do not simply reflect isotopic characteristics of ancient atmospheres but also, by using the theory, some of the isotopic characteristics of the normal glacier ice which was destroyed by melting and subsequently produced regelation ice can be reconstructed. Basal regelation ice at Byrd Station reflects an original ice source isotopically colder than the overlying normal ice, and may have formed during the penultimate glacial period, equivalent to stage 6 of the oceanic record.3. The subglacially derived debris typically found in basal regelation ice gives a complex strain response to a changing pattern of stresses produced by flow over an irregular subjacent bed. Thus, complex tectonic structures in this ice produce highly variable isotopic profiles. However, its gross isotopic characteristics can still be used to reconstruct some of its history. A sharp change in isotopic values tends to occur at the upper limit of basal regelation ice, the nature of which depends on the style and thickness of tectonic disturbance.4. Isotopic profiles in basal ice can be used to distinguish normal glacier ice from regelation ice, and give strong support to the view that regelation is the major process by which debris is incorporated into the base of a glacier.
Method of Measuring Liquid Water Mass Fraction of Snow by Alcohol Solution
Authors: Fisk D. 
Published: September 2017

Abstracta method of making field measurements of the liquid water fraction of snow has been developed in which a snow sample is dissolved in methanol to produce a temperature depression. The depression is linearly related to the liquid water content of the snow sample. a single operator can perform four to five measurements per hour with a maximum absolute error of 1.0%.
Some Comments on Glacier Flow
Authors: Finsterwalder Richard 
Published: September 2017

AbstractDrs. Orowan and Perutz have shown that glacier ice does not behave as a viscous fluid but is plastic like all crystalline materials. The present author discusses two observed types of ice flow:—(1) the normal, regular streaming flow in slow-moving glaciers; (2) Block-Schollen movement in swiftly flowing ice. Mention is made of the shear plane or laminar flow theory of Philipp. lt appears that Orowan s thesis is also applicable to Block-Schollen flow. The author agrees with Orowan on the fundamental point that when ice is subjected to shear stress a critical value of the shear stress exists beyond which the ice alters its consistency. But the author disagrees with Orowan in that he believes that below this critical value ice behaves as a viscous material, and he supports this view by reference to many phenomena, measurements and calculations.
The Significance of air Bubbles in Glacier Ice
Authors: Bader Henri 
Published: September 2017

AbstractThe study of air bubbles in glacier ice can give valuable information on the evolution of the ice. An analysis of the relation between an air bubble and the water associated with it shows that it may be possible to determine the maximum depth from which the ice containing the bubble has emerged. The shapes of the cavities containing water and air bubbles are described. They are found to reflect the anisotropism of ice crystals and reveal that the main crystallographic axis is polar. The question of the mechanism of elimination of air bubbles from glacier ice is raised. The investigations were made on the very old and coarse-grained ice from the foot of the Malaspina Piedmont Glacier in Alaska, which is a temperate glacier.
The Possible Future Behaviour of Berendon Glacier, Canada—A Further Study
Authors: Fisher David A. , Jones Stephen J. 
Published: September 2017

AbstractUntersteincr and Nye (1968) calculated the possible future movement of Berendon Glacier, B.C. These calculations are repeated using much improved data and a slightly different method for computing the datum state. The predictions that result are very similar to those found in the earlier work. It is concluded, however, from mass-balance data, that the chance of the glacier rising sufficiently in the next 25 years to be a danger to the mining installations situated near the snout of the glacier is much greater than was previously considered. The sensitivity of the theory to changes in input data is discussed.
Permafrost Occurrence in the Front Range, Colorado Rocky Mountains, U.S.A.
Authors: Ives Jack D. , Fahey Barry D. 
Published: September 2017

AbstractIn contrast to the extensive and rapidly growing body of knowledge on permafrost in the Eurasian and North American Arctic and sub-Arctic, little is known about permafrost occurrence in the high mountain regions of the world. Preliminary results of permafrost studies from the Colorado Rocky Mountains are presented.Above tree line (about 3 500 m) in the Front Range, scattered patches of permafrost begin to occur under wet sites blown free of snow in winter with a mean annual air temperature of about — 1.0°C. At greater elevations, with correspondingly lower mean annual air temperatures (extreme case — 9.0°C and 4400 m), permafrost becomes more extensive and probably exceeds 60 m in thickness. These initial results are derived from a skeleton ground-temperature observation program supplemented by indirect evidence and by data gathered from engineering and mining operations in the high country. It is probable that under the higher summits and ridge crests the alpine equivalent of the continuous zone of Arctic permafrost can be anticipated.
The Origin of Glacially Fluted Surfaces-Observations and Theory
Authors: Boulton G. S. 
Published: September 2017

Abstract
Studies of fluted surfaces beyond the margins of glaciers in Spitsbergen, Iceland,
Norway and the Alps show that almost all emanate from rigid obstructions, commonly boulders in
till. Field relations of flutes are described and it is shown that a relationship exists
between flute height and the height of the initiating obstruction. Subglacial observations
indicate that flutes form when till is intruded into tunnels which tend to open up in the lee
of obstacles. The pattern of strain implied by this process is shown to be reflected by micro-
and macrofabrics in the till. The commonly found occurrence of an average spacing between
flutes does not arise because of some rhythmic or periodic mechanism in the glacier, but is
produced by the random seeding of boulders which themselves generate flutes.
It is suggested that the term flute be used as a genetic rather than a descriptive
term, and be restricted to long parallel-sided ridges which reflect accurately the direction
of ice movement and which form when deformable subglacial materials are intruded into tunnels
which tend to open up on the lee sides of single rigid obstructions on the glacier
bed.
Deuterium, Tritium and Gross-Beta-Activity Investigations on Alpine Glaciers (Ötztal Alps)
Authors: Ambach W. , Eisner H. , Elsässer M. , Löschhorn U. , Moser H. , Rauert W. , Stichler W. 
Published: September 2017

By measuring the deuterium contents of stream water, spring water and melt water, as well as ice and snow samples, the mean contributions to melt water in the run-off from Hintereisferner have been estimated: that of melt water being 60% and that of spring water being 40% in the months of July to September. Spring water is characterized by very low deuterium contents, whereas ice-melt water and snow-melt water in the summer were found to have about the same, rather high deuterium content. The deuterium content in the run-off was subjected to considerable seasonal fluctuations owing to the changing shares in melt water and spring water. The deuterium contents in individual glacier run-offs show similar seasonal fluctuations and are furthermore characterized by a parallel shift of the deuterium concentrations, because of the different altitudes of catchment areas. Differences in the mean altitudes of catchment areas were estimated for the winter and summer discharges on the basis of the isotope altitude effect.The seasonal fluctuations of the tritium contents in glacier discharges are caused mainly by the melt water from glacier ice, which contains practically no tritium. Minimum values of tritium content in the runoff were thus found during the period of maximum ice ablation. The mean residence time of the base-flow in the ground-water system of a catchment area was roughly estimated to be a few years on account of the tritium content in the winter run-off and in the precipitations of past years.Profiles of the gross beta activity in firn cores, despite a reduced atmospheric fall-out during the past years, clearly show activity peaks in summer horizons that are suitable for net accumulation analyses. A characteristic peak in the profile of the tritium content which may be attributed to the net accumulation of 1962/63 is well suited for use as a reference horizon.
Mathematical Models of Ice Shelves
Authors: Shumskiy P. A. , Krass M. S. 
Published: September 2017

For flat external ice shelves, expanding freely in all directions, the problem of thermodynamics is one-dimensional. In the affine dimensionless system of coordinates, equations of the dynamics together with the rheological equation lead to the non-linear integro-differential equation involving the reduced temperature. In the quasi-steady case the boundary problem for this equation is solved by means of the method of combining asymptotic expansions. It is shown that if ice is coming from the upper and lower surfaces in the opposite directions the regime is unsteady because of the internal heat accumulation.The integro-differential equation for the temperature in the case of thinning internal ice shelves is more complicated, but it can be solved by a method analogous to the one mentioned above.
Surface Mass-Balance Variability Near “Byrd” Station, Antarctica, and its Importance to Ice Core Stratigraphy
Authors: Whillans I. M. 
Published: September 2017

AbstractThe local variability in surface mass balance (net snow accumulation) up-glacier from "Byrd" station, Antarctica, is due to the combined effects of year-to-year "climate" variations and of the surface microrelief clue to snow drifts and sastrugi. These variabilities are consistent with the variability in surface mass balance obtained from core stratigraphy (Gow, 1968), and are used in a discussion of the difficulties encountered with the deep "Byrd" station core in detecting annual layering by the stable oxygen-isotope ratio and the microparticle concentration techniques. The recognition of annual layers by these techniques requires that the snows of certain seasons be present in the measured section, but near "Byrd" station the microrclief is such that summer snow layers are not horizontally continuous and may be absent from a given section. At other sites on ice sheets, where the microrelief is less (less wind activity) or where the surface mass balance is larger, or both, less difficulty is anticipated in using the stable oxygen-isotope ratio and micro-particle-concentration techniques to identify annual layers.
Recording Wire Strainmeters on the Barnes Ice Cap, Baffin Island, Canada
Authors: Evans K. , Goodman D.J. , Holdsworth G. 
Published: September 2017

AbstractThe report describes an experiment to evaluate the use of geophysical (Cambridge-type) wire strainmeters for the rapid acquisition of strain-rate data and to compare strains on a large ice mass over gauge distances of 5 m, 50 m, and 1 km.Three continuously recording wire strainmeters were installed at the centre of two separate arrays of strain poles 10.6 km and 19.5 km from the ice divide on the Barnes Ice Cap. Data was collected between 24 April and 15 May 1976. The 1 km strain arrays had previously been measured in 1974 and 1975. The results show good agreement between the strainmeter data and the larger strain arrays at the 10.6 km site but differ at the 19.5 km site. When the daily means are calculated for the strainmeters at the 19.5 km site, the strain-rates show a possible periodic variation with an apparent period ofabout 11 d. Since there appears to be no direct correlation between the strainmeter signal and either temperature or pressure, the result is assumed to represent real varying strain within the ice.
Direct Measurement of Stress at the Base of a Glacier
Authors: Boulton G. S. , Morris E. M. , Armstrong A. A. , Thomas A. 
Published: September 2017

AbstractContact stress transducers were placed in subglacial bedrock and used to monitor continuously shear stress and normal pressure changes at the contact with the overriding glacier sole 100 m beneath the surface of the Glacier d’Argentière during periods in summer 1973 and spring 1975. The measured fluctuations in normal pressure and shear stress do not appear to be related to changes in sliding velocity. Analysis of the data reveals short-term fluctuations in normal pressure and shear stress which appear to be related to the passage of individual large debris particles or groups of particles over the transducer. The shear stress appears to be a function of the volume concentration of debris in the ice. The volume concentration at any point appears to be partially dependent on a “streaming” process by which basal debris-rich ice tends to flow around the lateral flanks of hummocks on the glacier bed. Where sub-glacial cavities occur, this streaming effect appears to be dependent on the extent of cavitation and thus on ice overburden pressure and velocity. It is suggested that this process can account for an apparent lag between changes in normal pressure and shear stress.The maximum ratio between shear and normal stress averaged over a period of 10 min was 0.44. This is equivalent to a spatial average over 0.3 cm. Debris concentrations in basal ice of up to 43% by volume occurred. It is suggested that concentrations of this order are common at the base of temperate glaciers and thus that a significant part of the drag at the base of a glacier may be contributed by frictional interactions between the basal-debris load and the bed.
Pattern of Ice Surface Lowering for Rennick Glacier, Northern Victoria Land, Antarctica
Authors: Mayewski Paul A. , Attig John W. , Drewry David J. 
Published: September 2017

AbstractRennick Glacier is one of the major ice drainages in northern Victoria Land. Unlike glaciers farther south along the Transantarctic Mountains, Rennick Glacier does not drain into the Ross Ice Shelf but flows directly into a seasonally ice-covered ocean. Therefore, current fluctuations of this glacier are unhampered by the dampening effects of the Ross Ice Shelf. The primary controls on the activity of this glacier and others in this region are mass balance and sea-level.Two major glacial events are recorded in the upper Rennick Glacier region. The location of erratics and glacially scoured features suggest that during the oldest or Evans glaciation ice covered all but the highest peaks in the region. Following this glaciation a re-advance produced the Rennick glaciation. Drift produced during this glaciation has a surface cover of unweathered clasts and is commonly found in the form of recessional moraines with associated ice-marginal lakes. Rennick Glacier is currently in a recessional phase of the Rennick glaciation. The phase is characterized by physical re-adjustments of local ice masses including progressive inland migration of the Rennick Glacier grounding line. To date the grounding line has migrated up to the mid-point of the glacier. This trend may be expected to continue.
The Formation and Composition of the Gas Content of Sea Ice
Authors: Tsurikov V. L. 
Published: September 2017

AbstractThe different factors contributing to the formation of the gas porosity of sea ice are: (Ia) gases captured during the formation of the initial ice cover, (Ib) gases released from solution during the initial freezing of sea-water, (Ic) the inclusion of gases rising from the sea bottom, (2a) the substitution of gas for brine drained from the ice during times of melting, (2b) the release of gas from the brine within the ice during the course of partial freezing, and (2c) the formation of voids filled with water vapour during the course of internal melting. An analysis is made of each of these processes and it is concluded that processes Ib, 2a, and 2C are important. Process Ic may also be a major effect but it is difficult to evaluate until the rate of gas release from the sea floor is better known. The migration of air pockets into the ice from the overlying snow is shown to be a possible but not a significant effect. Available data on the composition of gas in sea ice are reviewed and it is shown to be significantly different from air. Possible causes for these differences are discussed.The porosity of sea ice, i.e. the total relative volume of its gas plus its brine inclusions, is one of the factors strongly affecting its strength, as has been shown by Tsurikov (1947) and by Weeks and Assur (1968). In seas with high salinities the effect of the presence of brine within the ice will usually be the dominant factor. However on water bodies with low salinities the effect of the gas included within the ice may be greater than the effect of the brine. Despite its significance there have not been any attempts at a quantitative analysis of the entrapment of gas in sea ice. This paper is an attempt at such a study.
Flexural Wave Studies on the Basis of Single-Sensor Recordings
Authors: Taylor R. W. 
Published: September 2017

AbstractThe method described here provides a means of measuring flexural-wave dispersion and attenuation appropriate to a selected area, on the basis of single-sensor recordings made remote from the area of interest. The measured dispersion may then be inverted in the conventional manner to obtain thickness and elastic properties of the ice within the selected area. The procedure eliminates the need for equipment within the study area and minimizes the need for personnel within the area. As only a single sensor is necessary, the requirements for recording equipment and sensor cabling are also minimized. The method is suited to any study of flexural-wave dispersion from artificial sources and is ideally suited to the study of areas where personnel and equipment safety are a major concern.
Gravitational Stresses in Floating Ice Sheets
Authors: Evans R.J. , Parmerter R. Reid 
Published: September 2017

AbstractThis note is addressed to the determination of the in-plane components of stress in floating ice sheets due to gravity and the hydrostatic pressure in the water. The distribution and magnitude of these stresses are of interest with regard to crack propagation in sea ice. Two cases are considered. In the first, the ice sheet is formed on land by accretion at the top surface and then introduced into the water, such as happens in the Antarctic. In the second, the ice is formed in the water by accretion on the bottom, which is the usual situation in the Arctic pack ice.
An Analysis of the In-Situ Resistivity of Sea Ice in Terms of its Microstructure
Authors: Timco G. W. 
Published: September 2017

AbstractThe results of 66 Schlumberger geoelectric soundings on first-year sea ice are analysed to obtain average values of d.c. electrical resistivity both parallel ρ1 and perpendicular ρp to the long brine cell direction. This analysis yields ρ1 = 104 Ω m, 80 Ω m, 45 Ω m, and ρp = 298 Ω m, 230 Ω m, 129 Ω m for brine volumes νb of 40‰, 67‰, and 82‰ respectively. The observed dependence of ρ1 on νb is used in conjunction with a mixing formula for the electrical resistivity of a two-phase heterogeneous system to arrive at values of “average” brine cell lengths l for relatively warm sea ice. This treatment yields l ≈ 1.7 cm for 40‰ ≤νb≤ 70‰ with a rapid extension of brine cell lengths for brine volumes above c. 70‰.
A Field Study of Brine Drainage and Oil Entrainment in First-Year Sea Ice
Authors: Martin Seelye 
Published: September 2017

AbstractFrom field observations this paper describes the growth and development of first-year sea ice and its interaction with petroleum. In particular, when sea ice initially forms, there is an upward salt transport so that the ice surface has a highly saline layer, regardless of whether the initial ice is frazil, columnar, or slush ice. When the ice warms in the spring, because of the eutectic condition, the surface salt liquifies and drains through the ice, leading to the formation of top-to-bottom brine channels and void spaces in the upper part of the ice. If oil is released beneath winter ice, then the oil becomes entrained in thin lenses within the ice. In the spring, this oil flows up to the surface through the newly-opened brine channels and distributes itself within the brine-channel feeder systems, on the ice surface, and in horizontal layers in the upper part of the ice. The paper shows that these layers probably form from the interaction of the brine drainage with the percolation of melt water from surface snow down into the ice and the rise of the oil from below. Finally in the summer, the oil on the surface leads to melt-pond formation. The solar energy absorbed by the oil on the surface of these melt ponds eventually causes the melt pond to melt through the ice, and the oil is again released into the ocean.