bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-climatic control of glacier-terminus fluctuations in the Wrangell and Chugach Mountains, Alaska, U.S.A.
Authors: Sturm Matthew , Hall Dorothy K. , Benson Carl S. , Field William O.
Published: September 2017

Fluctuations of glacier termini were studied in two regions in Alaska. In the Wrangell Mountains, 15 glaciers on Mount Wrangell, an active volcano, have been monitored over the past 30 years by surveying, photogrammetry and satellite. Results, which are consistent between different methods of measurement, indicate that the termini of most glaciers were stationary or retreating slightly. However, the termini of the 30 km long Ahtna Glacier and the smaller Center and South MacKeith Glaciers began to advance in the early 1960s and have advanced steadily between 5 and 18 m a−1 since then. These three glaciers flow from the active North Crater, where increased volcanic heating since 1964 has melted over 7 x 107 m3 of ice. We suspect that volcanic meltwater has changed the basal conditions for the three glaciers, resulting in their advance.

The terminus fluctuations of six tide-water and near-tide-water glaciers in College Fjord, Prince William Sound, have been monitored since 1931 by surveying, photogrammetry and, most recently, by satellite imagery. Harvard Glacier, a 40 km long tide-water glacier, has been advancing at an average rate of nearly 20 ma−1 since 1931, while the adjacent Yale Glacier has retreated at approximately 50 ma−1 during the same period though, for short periods, both of these rates have been much higher. The striking contrast between the terminus behavior of Yale and Harvard Glaciers, which parallel each other in the same fiord, and are derived from the same snowfield, supports the hypothesis that their terminus behavior is largely the result of dynamic controls rather than changes in climate.
Estimating ice temperature from short records in thermally disturbed boreholes
Authors: Humphrey Neil
Published: September 2017

A technique to estimate undisturbed ice temperature is discussed for sensors placed in boreholes that have been heated to the melting point during drilling, and for which only a limited time span of temperature record is available. A short temperature record after the hole refreezes commonly results when using hot-water or steam drills, where measurements are constrained by logistics, ice deformation, sensor drift or other problems, or where the refreezing time is long because of near-freezing ice temperatures or large hole sizes. Short data records are also typical in ongoing drilling programs where temperature information may be necessary for the program itself. Building on analyses by Lachenbruch and Brewer (1959) and a numerical model by Jarvis and Clarke (1974), it is shown that estimates of undisturbed temperatures can be made from records of temperature that extend only marginally beyond the initial refreezing. Complex effects of hole size, heating history, and the thermodynamic and geometrical effects of a moving boundary (the freezing borehole walls) are important to temperature decay immediately after freeze-up, so that the standard technique of comparing temperature decay to an inverse of time model is not applicable, and comparsion has to be made to a numerical model of heat flow to a refreezing borehole. Data from Ice Stream B, Antarctica, are compared to the numerical model to illustrate the technique. Data are also compared to simpler (inverse time) thermal models, and a potential for error is pointed out, since a short data record can be spuriously matched with the simpler, one or two free-parameter, models.
Ice Dynamics and Thermal Regime of Taylor Glacier, South Victoria Land, Antarctica
Authors: Robinson P. H.
Published: September 2017

Glaciological data collected from Taylor Glacier have been used to assess aspects of the dynamics and thermal regime of the glacier. Mass-balance studies suggest that the glacier is in near equilibrium. The thermal condition of the basal ice over much of the ablation area was calculated from estimates of the geothermal heat influx and measurements of near-surface ice temperatures, ice velocities, and ice thickness. It was found that, in as much as 50% of the lower ablation area, the basal ice may be melting.
Relationship Between Bore-Hole Closure and Crystal Fabrics in Antarctic Ice Core from Cape Folger
Authors: Thwaites Richard J. , Wilson Christopher J. L. , McCray Anthony P.
Published: September 2017

Two holes were drilled to depths greater than 300m in the Antarctic ice sheet, near Cape Folger on the Law Dome. The holes underwent considerable closure below 250m with localized strain-rates as high as 1 to 1.5×10−6 s−1. The closure observed in holes was non-uniform and occurred in zones 0.5 to 3 m wide. These Zones parallel the flow plane in the ice mass and are associated with a distinct domainal structure. High-closure zones are characterized by interlocking and irregular-shaped ice grains with many sub-horizontal c-axes and only occasional c-axis clusters at a high angle to the flow plane. Low-closure zones contain tabular grains with the long dimension parallel to the flow plane, abundant deformation features and a predominance of c-axes oriented at a high angle to the flow plane. The relationship between closure rate and c-axis fabric is attributed to marked plastic flow by intracrystalline slip on the basal plane to produce higher closure in areas where there is a greater variation in c-axis orientation. This deformation is attributable to overburden pressure and hence is related to depth, and is independent of shear within the main body of the ice mass.
The Use of Hypsometry to Indicate Long-Term Stability and Response of Valley Glaciers to Changes in Mass Transfer
Authors: Furbish D.J , Andrews J.T.
Published: September 2017

A simple equation is derived relating the net mass-balance and hypsometric curves of a steady-state valley glacier. It is used to examine how valley shape is linked to disparate extents and responses of glaciers subjected to similar climatic conditions. Examples are given which show that area-based indices (e.g. AAR) for estimating the equilibrium line altitude (ELA) may be subject to a substantial built-in variance because they implicitly rely upon similarity of glacier shape and regimen over a region. If accurate topographic maps are available, the equation may be used to infer the regimen of modern glaciers in the form of a dimensionless ratio of net mass-balance gradients. Alternatively, if similar information is available concerning regional glacier regimen, disparate extents and responses may be collectively utilized to estimate values of ELA or to infer climatic influence, taking glacier hypsometry into account.
Rates and Mechanisms of Iceberg Ablation in the D’Urville Sea, Southern Ocean
Authors: Keys J. R. , Williams K. L.
Published: September 2017

Wave action causes ablation in a narrow zone around an iceberg’s waterline, at up to 0.3 m per day, in water of −1°C with waves up to 0.4 m high. Subsequent subaerial calving of ice from iceberg sides takes place up to a similar rate. Submarine melting is an order of magnitude slower than wave action but acts over the largest part of an iceberg. Ablation rates derived theoretically or statistically elsewhere for comparable environmental conditions, are in reasonable agreement with those measured here. Drifting icebergs trail a plume of mixed, slightly cooled and diluted sea-water in their wake.
Shock-Wave Studies Of Ice Under Uniaxial Strain Conditions
Authors: Larson Donald B.
Published: September 2017

Shock-wave studies of ice under uniaxial strain conditions have been conducted at stress levels up to 3.6 GPa. A light-gas gun accelerated the flat-faced projectile used to impact the ice-containing targets. The ice samples were initially at ambient pressure and at temperatures of –10 ± 2° C. Gages were implaced at different distances in the ice along the path of the shock wave to measure particle velocity time histories inside the ice samples. The recorded time histories of particle velocity show a precursor wave with an average wave velocity of 3.7 km/s and an average particle velocity amplitude of 0.06 km/s. This wave is travelling at a wave velocity approximately 10% greater than longitudinal sound speed and is believed to originate because of the onset of melting of ice I.

The particle velocity data from these experiments were converted to stresses and volumes using Lagrangian gage analysis and the assumption of a simple non-steady wave. This conversion provides a complete compression cycle (which includes both loading and unloading paths) for comparison with static measurements. All experiments show the onset of melting at 0.15 to 0.2 GPa. Experiments with maximum stress states between 0.2 and 0.5 GPa yield results which suggest that a mixed phase of ice I and liquid water exists at these conditions. For maximum loading stresses between 0.6 and 1.7 GPa the experimental results suggest that the final state is predominately ice VI. In these experiments the specific volume upon compression is changed from 1.09 m3/Mg to approximately 0.76 m3/Mg, which represents compaction of approximately 30%. The unloading paths determined from these experiments indicate that ice VI remains in a “frozen” or metastable state during most of the unloading process. This hysteresis in the compression cycle gives rise to a large “loss” of shock-wave energy to the transformation process. At stress levels above 2.2 GPa, ice VII should be the stable form for water according to static compression measurements. Experimental data at 2.4 and 3.6 GPa suggest that ice VII may be formed but these results indicate a mixed phase of ice VI and ice VII rather than complete transformation to ice VII.
Ice On Planets of the Solar System
Authors: Krass M.S.
Published: September 2017

Several aspects of space glaciology are considered in the paper. Estimates of the water content of the Earth, Mars, and the Galilean moons of Jupiter are corrected. A considerable proportion of the total amount of water in the solar system is localized near Jupiter; part of this water is contained as ice in glaciations, glacial caps, and ice crust on the planets. Ice is one of the main components of the surface of some planets. The major amount of ice on Mars is contained in a permafrost layer of mean thickness about 3 km. The model of an ice crust floating on a water mantle is considered for Jupiter’s moon Europa. It is shown that for definite values of certain parameters this crust may be subject to destruction due to the instability of its proper oscillations, which explains the numerous systems of fractures and cracks observed on Europa’s surface. The stress-strain state of such an ice crust is calculated within the framework of a non-linear thermo-elasticity model. The role of short-period temperature variations at Europa’s surface is estimated and the peculiarities of relief observed on this planet are analysed.
Electrical Resistivity of Ice from the Antarctic Peninsula, Antarctica
Authors: Reynolds John M. , Paren J. G.
Published: September 2017

Georesistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that:

(a)

the resistivity of deep ice is similar to that of other Antarctic ice shelves,

(b)

the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character.

A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105 Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice.
A Mathematical Model for Perched Block Formation
Authors: Patterson E. A.
Published: September 2017

A mathematical model for the formation of perched blocks on glaciers due to differential ablation is developed by considering energy balances. The model is applied to naturally positioned rocks on Bersærkerbræ, Greenland. The model predicts correctly whether a rock will perch or sink in eleven out of twelve cases. For artificially positioned small rocks of mean dimension 0.2 m, the model has a 53% success rate. The reduced performance is probably due to the thicknesses of the rocks being of similar magnitude to the range of relief of the glacier surface.
Avalanche Tarns
Authors: Fitzharris B. B. , Owens I. F.
Published: September 2017

Avalanche tarns are a particular morphological form of avalanche impact and sixteen of these features are described from the Fiordland region of New Zealand. Average area of the tarns is 11000 m2. Profiles are given for eight of the avalanche paths where such tarns occur. All are found at the base of very steep avalanche tracks (slopes 38–59°), where there are no fans, so that there is an abrupt change of slope with the valley floor. The plunging avalanches which cause the tarns may have a mass of up to 300000 tonnes and impact pressures of more than 600 kN/m2, although no direct measurements are available.
The Natural Oscillations of an Ice-Covered Channel
Authors: Green Theodore
Published: September 2017

The natural modes of oscillation of an infinitely long, ice covered channel are considered, using the hydrostatic approximation, and assuming the ice to behave elastically. The dispersion relation, mode shape, and associated force on the channel wall are found for the lowest three modes. Special attention is paid to the limitations associated with the hydrostatic and elastic approximations.
The Shear Strength Characteristics of Frozen Coarse Granular Debris
Authors: Nickling W.G. , Bennett L.
Published: September 2017

The effect of ice content and normal load on the shear strength characteristics of a frozen coarse granular debris was investigated. 31 shear tests were carried out in a modified shearbox allowing a sample temperature of (–1.0 ± 0.2)° C and a load rate of 9.63 × 10−4cm/min. The tests showed that as the ice content of the frozen debris was increased from 0% (under-saturated) to 25% (saturated), sample shear strength was markedly increased. In contrast, sample shear strength was reduced as ice content was increased from 25% (saturated) to 100% (supersaturated). The changes in shear strength with increasing ice content were attributed directly to changes in internal friction and the cohesive effects of the pore ice. The shear tests also indicate that shear strength increases with increasing normal load up to a critical limit. Above this limit, dilatancy is suppressed causing the shear strength to decrease or remain relatively constant with increased normal load.

The stress-strain curves of the 31 tests indicated that samples with higher ice contents tended to reach peak strength (τP) with less displacement during shear. Moreover, the difference between τpand τr(residual strength) was lowest for pure polycrystalline ice and highest for ice-saturated samples. The Mohr-Coulomb failure envelopes displayed very distinctive parabolic curvilinearity. The degree of curvature is thought to be a function of ice creep at low normal loads and particle fracture and crushing at high normal loads.
Snow Wetness Measurement by Fluorescent Dye Dilution
Authors: Davis Robert E. , Dozier Jeff
Published: September 2017

The fluorescent dye dilution method for determining the liquid-water content in snow is based on measuring the concentration change of a solution when it is mixed with snow. Samples for analysis can be obtained rapidly and reliably, and, unlike calorimetric or equilibrium-temperature methods, field use requires no on-site data analysis.
Electrical Resistivity Soundings of Glacier Beds: A Test Study on Grubengletscher, Wallis, Swiss Alps
Authors: Haeberli Wilfried , Fisch Werner
Published: September 2017

Electrical resistivity sounding, using electrodes which are lowered directly to the ice–rock interface in bore holes, is proposed as a technique for studying the exact position of glacier beds, as well as their lithological characteristics. A test study is described on Grubengletscher, a partially cold Alpine glacier in Switzerland. Results of soundings along a 400m long profile indicate that previous depth determinations, based on radio echo-soundings, were in general accurate to within less than 5% of the actual ice thickness. The results also show that the glacier rests on non-consolidated sediments of considerable thickness. The proposed method could add substantial information about glacier sliding and glacier erosion, if applied alongside conventional deep drilling projects.
Accelerating Flow of the Brunt Ice Shelf, Antarctica
Authors: Simmons D. A. , Rouse J. R.
Published: September 2017

Position fixes made at the British Antarctic Survey station, Halley, on the Brunt Ice Shelf are considered for the period 1968–82. These show an initial westward velocity of approximately 400 ma−1 rising to over 700 m a−1 by the end of the period. The data are well fitted by two straight lines. The first for 1968–71 has a slope 430 m a−1 in agreement with that found by Thomas (1973) for the period up to 1968. The second for 1972–83 has a slope 740 ma −1, a large increase sustained for up to 10 years.
Spatial and Temporal Variations in Electrical Conductivity in a Pro-Glacial Stream System
Authors: gurnell A. M. , Fenn C. R.
Published: September 2017

Spatial and temporal observations of electrical conductivity during the summers of 1978 and 1981 on the pro-glacial stream sytem of glacier de Tsidjiore Nouve, Valais, Switzerland, are described. Three space–time scales of electrical conductivity variations are considered: single-site, hourly monitoring for a two-month period; multiple-site sampling over 12 h periods using a 1 h sampling interval, and multiple-site sampling over monthly periods using a 24 h and 48 h sampling interval. Detailed analysis of the information from the three scales shows that the sampling strategies employed can reliably be used to investigate space–time patterns in the data. The results demonstrate that there are diurnal cycles in both electrical conductivity and discharge which are slightly different in form and which are out of phase with one another at the same site. Simultaneous multiple-site sampling of electrical conductivity shows that the tributary streams draining the glacier snout exhibit complementary shifts in electrical conductivity between ablation seasons, between days, and within days. The significance of these complementary shifts in tributary electrical conductivity are discussed in the light of possible source areas, storage, and routing fluctuations of melt water draining from the glacier.
Normal Stress Effects in the Creep of Ice
Authors: McTigue David F. , Passman Stephen L. , Jones Stephen J.
Published: September 2017

Most non-linear fluids for which the appropriate measurements have been made exhibit non-zero and unequal normal stress differences in shearing flows. Power-law models such as Glen’s law cannot represent this phenomenon. The simplest constitutive equation that does embody normal stress effects defines the second-order fluid. An exact analytical solution for biaxial creep of such a fluid is fit to data from four tests on polycrystalline ice. The model gives an excellent representation of both primary and secondary creep. The fits provide values for the three material constants. These coefficients indicate positive first and second normal stress differences. One consequence is the prediction that a steady open-channel flow will exhibit a longitudinal free-surface depression of up to several meters for sufficiently thick ice on steep slopes. In addition, the compressive principal stress at the channel margin is decreased and the tensile principal stress is increased in magnitude over those predicted by models without normal stresses. The normal stresses thus favor the formation of crevasses. Furthermore, the angle these crevasses form with the channel margin is decreased.
Mass Balance of the Greenland Ice Sheet at Dye 3
Authors: Reeh Niels , Gundestrup Niels S.
Published: September 2017

The mass balance of the Greenland ice sheet at Dye 3 is estimated on the basis of observations of ice thickness, accumulation rate, surface velocities, and surface strain-rates. The calculations indicate a rate of increase of surface elevation of 3 cm/year, with 95% confidence limits of −3 cm/year and +9 cm/year. Previous estimates of the mass balance of the Greenland ice sheet by the same method reported large imbalances; these are most probably due to lack of precise data and the use of quantities measured at the surface as representative of depth-averaged quantities. The most reliable observations indicate that the interior regions of the Greenland ice sheet are at present thickening at a rate of a few centimetres per year; a contributing cause for this may be the slow thinning of a bottom layer of relatively soft Wisconsin ice.
Icing on a Non-Rotating Cylinder Under Conditions of High Liquid Water Content in the Air: I. Form and Size of Ice Deposits
Authors: Launiainen Jouko , Lyyra Markku
Published: September 2017

Ice accretion on a non-rotating cylinder was studied under icing conditions involving a wet-growth (glaze) process. Experiments were performed in an outdoor wind tunnel designed for icing studies. In this paper, the experimental method is introduced and the characteristics of form, size, and time development of deposits are given. In terms of freezing conditions, these characteristics were found to be very complex, in which all the external effects: air temperature, wind conditions, liquid water content in the air, and accretion time, are of the same order of importance. In a wet-growth process there exists above the icing surface a water film, the behaviour and dynamics of which are affected by various variables. The water film seems to play an important role in the wet-growth icing.
Drainage-Basin Characteristics of Nordaustlandet Ice Caps, Svalbard
Authors: Dowdeswell Julian A.
Published: September 2017

Recent mapping of ice-surface and bedrock topography from airborne radio-echo sounding has shown that the ice caps of Nordaustlandet, Svalbard, are divided into a series of well-defined drainage basins. Three lines of evidence indicate that several distinctive modes of ice-flow regime characterize these basins: (1) comparison between observed and theoretical ice-surface profiles; (2) analysis of driving stresses; and (3) observations of ice-surface features on satellite imagery and air photographs. The drainage basins are inferred to behave in the following ways. First, basins with low driving stresses and surface profiles, some of them clearly stagnant, are associated with the quiescent phase between glacier surges. Secondly, the ice streams draining southern Vestfonna have low surface profiles, relatively low driving stresses, and marked shear zones at their margins. They are interpreted to be flowing continuously at a relatively faster rate than the ridges between them. Basal melting, perhaps combined with substrate deformation, is probably responsible for the regime of these glaciers. Thirdly, the remaining basins studied on Nordaustlandet have relatively high marginal driving stresses and high surface profiles. They are interpreted to be frozen to their beds, at least near their margins. Some of these basins may also surge, particularly those where a part of the basin is below sea-level, and therefore is probably underlain by considerable thicknesses of deformable sediments.
Assessment of mass-balance variations within a sparse stake network, qamanârssûp sermia, west greenland
Authors: Braithwaite Roger J.
Published: September 2017

Variations of area-averaged annual balance can be calculated from sparse stake networks, if the specific balances satisfy a simple version of the linear model proposed by Lliboutry. The linear model is tested with 4 years of data at 13 stakes on Qamanârssûp sermia, West Greenland, and is satisfied with a model error of ±0.34 m water equivalent. From analyses of data from three stakes a few metres apart, the random error in the measurement of annual balance is estimated to be greater than ±0.23 m water equivalent. The variation in balance for the 4 years is ±0.52 m water equivalent which reflects the year–to–year variation in climate. The shortness of the present data series is admitted and its continuation is recommended.
Combined measurements of Subglacial Water Pressure and Surface Velocity of Findelengletscher, Switzerland: Conclusions about Drainage System and Sliding Mechanism
Authors: Iken Almut , Bindschadler Robert A.
Published: September 2017

During the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.

The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.

The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.
Changes in microstructure of snow under large deformations
Authors: Edens Michael Q. , Brown Robert L.
Published: September 2017

A set of microstructural variables is selected to characterize the behavior of snow. Corresponding mathematical relations from quantitative stereology theory are presented along with relations and techniques required for numerical evaluation. An experimental investigation is carried out to determine changes in these variables for snow subjected to large compressive deformations. The micro-structural variables studied included coordination number, grain-size, bond radius, neck length, pore-size, free surface area and grains/unit volume. Measurements at several stages of deformation are used to evaluate the changes in the microstructure as functions of deformation. Microstructure measurements of six snow samples subjected to confined compression tests are presented for pre-compressed and compressed states, corresponding to final stresses of 0.387, 0.77 and 1.55 MPa. Grain-size and bond radius were found to go through finite changes during compression, although the variation of bond radius was more complicated in nature. The coordination number and number of bonds/unit volume were found to go through large changes during compression, while specific free surface area was found to increase by 100% due to grain- and bond-fracture processes. No discernible patterns of change in neck length could be found in the experiments. A close relationship between some of the microstructural variables and the stress response of the material was observed. These results serve to contribute to the presently available data and understanding of the microstructural behavior of snow.
The topology of ice-sheet centres
Authors: Nye J.F.
Published: September 2017

An ice sheet will, in general, possess points where the horizontal component of velocity is zero, and some of these will be ice centres, occurring close to summits. The paper examines the possible flow patterns near such points. The corresponding horizontal strain-rate pattern is studied by considering an ice sheet which initially has perfect circular symmetry about a vertical axis. Before perturbation there is an isotropic point for the horizontal surface strain rate at the centre. It may be shown, on purely topological grounds and without any reference to the mechanism of flow, that, when the symmetry is broken, this point, being degenerate and structurally unstable, breaks up into two structurally stable components. The breakup always occurs in essentially the same way. Around the two component points the trajectories of principal strain-rate directions always have the lemon pattern. The contours of equal principal strain rate around them are usually hyperbolic; however, if the unperturbed flow pattern had a very pronounced spiral character, they would be elliptic. This behaviour is in contrast to that of the ice centre itself, which remains unsplit.
Ice physical properties, structural characteristics and stratigraphy in Hobson’s Choice Ice Island and implications for the growth history of East Ward Hunt Ice Shelf, Canadian High Arctic
Authors: Jeffries Martin O. , Serson Harold V. , Krouse H. Roy , Sackinger William M.
Published: September 2017

Hobson’s Choice Ice Island is a tabular iceberg that calved in 1982-83 from East Ward Hunt Ice Shelf, N.W.T., Canada. Four ice cores have been analyzed for ice-crystal size, structure and fabric, bulk density, liquid electrical conductivity, δ18O and tritium. This has enabled a complete characterization of the physical properties and the structural characteristics of the ice-shelf component of Hobson’s Choice Ice Island and the first ever study of the stratigraphy and growth history of East Ward Hunt Ice Shelf. The δ18O values range from -34.6 toand indicate that all the ice is derived directly and/or indirectly from precipitation. High tritium values occur only in the lowermost 5 m of the ice shelf in a layer named stratum B. The tritium is anthropogenic and indicates bottom accretion of fresh-water ice since 1952, most likely from fresh water flowing out of Disraeli Fiord below the eastern ice shelf. Above this deepest and youngest ice layer is a 35-38 m thick, unconformable layer (stratum A) comprising three ice types: iced-firn, slush ice and lake ice. This depositional-superimposed ice represents past surface accumulation, which, according to δ18O and ice-crystal structure and size variations, occurred in three major periods, each interrupted by major ablation periods. Fresh water flowing out of Disraeli Fiord below the ice shelf during those warm intervals was the most likely agent responsible for the ablation and eventual complete loss of the original sea-ice platform on which stratum A initially accumulated. The three sub-strata of stratum A vary in thickness from core to core and suggest that there has been an inversion of relief during each ablation period. The different properties and occurrences of the three superimposed ice types are due primarily to past topographic variability.
Polythermal conditions in arctic glaciers
Authors: Blatter Heinz , Hutter Kolumban
Published: September 2017

Englacial temperature measurements in Arctic valley glaciers suggest in the ablation zone the existence of a basal layer of temperate ice lying below the bulk of cold ice. For such a polythermal glacier, a mathematical model is presented that calculates the temperature in the cold part and the position of the cold-temperate transition surface (CTS). The model is based on the continuum hypothesis for ice and the ice-water mixture, and on the conservation laws for moisture and energy. Temperate ice is treated as a binary mixture of ice and water at the melting point of pure ice. Boundary and transition conditions are formulated for the free surface, the base and the intraglacial cold-temperate transition surface. The model is reduced to two dimensions (plane flow) and the shallow-ice approximation is invoked. The limit of very small moisture diffusivity is analysed by using a stationary model with further reduction to one dimension (parallel-sided slab), thus providing the means of a consistent formulation of the transition conditions for moisture and heat flux through the CTS at the limit of negligibly small moisture diffusion.

The application of the model to the steady-state Laika Glacier, using present-day conditions, results in a wholly cold glacier with a cold sole, in sharp contrast to observations. The present polythermal state of this glacier is suspected to be a remnant of the varying climatic conditions and glacier geometry during the past few centuries. Steady-state solutions representing a polythermal structure can indeed be found within a range of prescribed conditions which are judged to be realistic for Laika Glacier at the last maximum extent of the glacier.
Crack-fabrication techniques and their effects on the fracture toughness and CTOD for fresh-water columnar ice
Authors: Wei Y. , DeFranco S.J. , Dempsey J. P.
Published: September 2017

The effects of notch acuity (crack-tip sharpness) on the fracture toughness of S2 ice were investigated using six groups of single-edge-notched-bend (SENB) specimens with different crack (or notch) root radii fabricated by six different methods. The mean value and standard deviations of the apparent fracture-toughness valuesKQof the specimens with blunt notches were significantly higher than those of the specimens with sharp cracks. The results presented in a plot of fracture toughness versus, wherepis the crack-tip radius, provide an estimate of the required notch acuity for fracture-toughness testing. The microstructural features in the immediate vicinity of the crack tip and the crack-tip geometry govern the magnitude of the apparent fracture toughness of the ice. The crack-tip-opening-displacement (CTOD) measured in this study indicates the existence of microplastic deformation in the vicinity of the crack tip at the initiation of unstable fracture.
A numerical simulation of supraglacial heat advection and its influence on ice melt
Authors: Moore R. D
Published: September 2017

Energy exchange between the atmosphere and a melting glacier surface is mediated by the presence of a water layer. Under conditions of rapid melt and/or heavy rainfall, the possibility exists that a supraglacial run-off layer can advect sensible heat and influence the spatial variations of melt. The potential magnitude of such advection was investigated by numerically solving differential equations expressing the mass and energy balances of a two-dimensional run-off layer. Solutions were obtained for conditions typical of rainfall events, in which the potential for supraglacial heat advection should be maximal. The solutions indicate that advection cannot influence macro-scale melt patterns and surface morphology, except perhaps under heavy rainfall and/or rapid melt conditions, but can possibly cause micro-scale variations in ice melt. One-dimensional energy-balance models, which have normally been applied over glacier surfaces, should remain valid for most conditions.
The Crystalline Structure of Ice
Authors: Owston P. G. , Lonsdale Kathleen
Published: September 2017

Only one form of natural ice has been proved to exist at ordinary pressures. The positions of the oxygen atoms are known definitely from X-ray investigation. These form an open-work structure in which each oxygen is surrounded tetrahedrally by four others, the whole system having hexagonal symmetry. The positions of the hydrogen atoms between each pair of oxygens are not known with certainty, perhaps because they may be continually changing. Curious diffuse X-ray patterns, which are related to the temperature of ice, have yet to be explained in detail, but may throw light on the atomic movements. A cubic form of ice may exist at temperatures below −70° C. and under special conditions, and some less symmetrical high pressure forms have also been studied.
The Constitution of Valley Glaciers
Authors: Sharp Robert P.
Published: September 2017

Ice streams composing a compound valley glacier may be juxtaposed, inset or superimposed, and Demorest’s concepts of ice flowage provide a plausible explanation for these relations. If valley floors are accordant, juxtaposition results because the waxing force of gravity and obstructed gravity flow in the tributary glacier overcomes the waning force of obstructed extrusion flow from the trunk glacier enabling the tributary to force its way into a juxtaposed position with the trunk glacier in the main valley. If discordance in valley floors is less than the thickness of the trunk glacier, an insert position develops by the same mechanism. If the discordance is greater than the thickness of the trunk glacier, superimposition results. Locally, superimposed or inset relations may be established by exceptionally rapid advances, even with accordant valley floors, but any superimposed ice stream shortly becomes inset by sinking into the underlying ice, at least in temperate glaciers.
A Model for Sorted Patterned-Ground Regularity
Authors: Ray R. J. , Krantz W. B. , Caine T. N. , Gunn R. D.
Published: September 2017

Sorted patterned ground refers to polygons, nets, or stripes defined by rocky borders which are the result of sorting in soil subjected to frost action. This paper presents a model in which convection cells, driven by unstable density stratification in the aqueous phase, result in uneven melting of the underlying ice front during thawing. The resulting undulatory ice front with regularly spaced peaks and troughs provides the pattern which results in the regularity observed for certain types of patterned ground. In addition, the model predicts the width to depth-of-sorting ratio for both polygons and stripes, and explains the characteristic hexagonal shape of sorted polygons, the transition from sorted polygons to sorted stripes on sloped terrain, and the formation of sorted polygons under water. The predicted ratio of width to depth-of-sorting of 3.81 for sorted polygons is compared with the ratio of width to depth-of-sorting of 3.57 found from a linear regression analysis of 18 field study data.
Some Aspects of the Cenozoic Glaciation of Southern Victoria Land, Antarctica
Authors: Brady Howard , McKelvey Barrie
Published: September 2017

Palaeoglacial evidence at three sites in southern Victoria Land has been examined to consider the possible uplift of the Transantarctic Mountains through the East Antarctic ice sheet prior to the Middle Miocene. A Cenozoic tillite at Mount Feather and a striated pavement at Mount Brooke pre-date uplift. Another tillite remnant adjacent to Odell Glacier near Mount Brooke post-dates the uplift and is locally derived. This tillite, together with the Mount Feather tillite, has been previously placed in the Sirius Formation, a term that the authors abandon as it covers tillites of varying ages. Basement complex derived clasts in the Mount Feather tillite. previously reported by these authors, could be inherited from the Jurassic Mawson Formation or the Permian Metschel Tillite but they still provide evidence that the Mount Feather tillite was deposited by a regional glaciation.
Derivation of Voellmy’s Maximum Speed and Run-Out Estimates from a Centre-of-Mass Model
Authors: McClung D. M.
Published: September 2017

The commonly used maximum speed and run-out equations for flowing avalanches given by Voellmy’s (1955) method are considered from a more general model proposed by Perla and others. (1980). Equations analogous to those of Voellmy are derived and the approximations are defined from the point of view of the more general model.
Mode of Formation of “Ablation Hollows” Controlled by Dirt Content of Snow
Authors: Rhodes Jonathon J. , Armstrong Richard L. , Warren Stephen G.
Published: September 2017

A contradiction has existed in the literature as to the conditions favoring formation of “ablation hollows” (“suncups”) on a melting snow surface. Some experiments find that these features grow under direct sunlight and decay in overcast, windy weather; whereas others find just the opposite result, that they grow best under cloudy, windy conditions and decay if exposed to direct sunlight. We find that the hidden variable in past experiments, which acts as a switch to determine which mode of formation can operate, is the absence or abundance of dark insoluble impurities in the snow. Direct sunlight causes ablation hollows to grow in clean snow and to decay in dirty snow (for dirt content below a critical value), because the dirt migrates to the ridges between the hollows, lowering the albedo at the ridges. By contrast, when ablation is dominated by turbulent heat exchange, the presence of dirt favours development of ablation hollows because the dirt migrates to the ridges and insulates them; albedo reduction has a negligible effect on ablation.

This hypothesis is supported by an experiment which showed that the presence of a thin layer of volcanic ash on the snow inhibited formation of ablation hollows under direct sunlight.
A Transient Temperature Solution for Bore-Hole Model Testing
Authors: Hanson Brian , Dickinson Robert E.
Published: September 2017

Transient temperature variations in a vertical column of ice with horizontally uniform conditions, constant vertical strain-rate and specified surface temperature, and basal heat flux can be calculated analytically. The solution consists of eigenfunctions which are forms of the confluent hypergeometric function. This solution shows that advection and diffusion have clearly separated areas of dominance, with diffusion being a sufficient approximation for small-scale perturbations in the temperature profile and advection placing an upper limit on the response time of the ice sheet as a whole. This solution is useful for analysis and testing of numerical models, for evaluation of the response time of an ice sheet and for exploratory analysis of real bore-hole data. The lowest eigenvalue of the solution determines the time-scale for transient decay of temperature anomalies. The time-scale can be determined for more general strain-rates using a finite-difference approximation to the linearized energy-balance equation.
Topoclimatic Studies of a High Arctic Plateau Ice Cap
Authors: Bradley Raymond S. , Serreze Mark C.
Published: September 2017

Meteorological observations on and around a small, exposed plateau ice cap on north-eastern Ellesmere Island, N.W.T., Canada, were carried out in the northern summers of 1982 and 1983. The objective was to assess the effect of the ice cap on local climate as the melt season progressed. In 1982, seasonal net radiation totals were lowest on the ice cap and greatest at the site farthest from the ice cap. The ice-cap site received only 35% of net radiation totals on the surrounding tundra. This reflects a gradient in albedo; albedo changed most markedly away from the ice cap as the summer progressed. A thermal gradient was observed along a transect perpendicular to the ice-cap edge; this gradient was greatest at low levels (15 cm) and was maximized under cloud-free conditions. The “cooling effect” of the ice cap was less at the start of the ablation season than later. Low-level inversions occurred more frequently over the ice cap than over the snow-free tundra. Overall, melting degree days on the ice cap were only 40–65% of those on the adjacent tundra. A model of interactions between the atmosphere and a snow and ice cover, or a snow-free tundra/felsenmeer surface is proposed. Observations indicate that the ice cap has a cooling effect on the lower atmosphere relative to the adjacent snow-free tundra; this effect is absent when snow cover is extensive (as in 1983).
A Major Calving Event of Jakobshavns Isbræ, West Greenland, on 9 August 1982
Authors: Epprecht W.
Published: September 2017

On 9 August 1982, the calving of a large ice mass, approximately 0.3 km x 1.5 km in size, from Jakobshavns Isbræ was filmed. The event, which took place as the tide was rising, is described by means of picture sequences from the ciné film. First, a large transverse crevasse opened in the glacier. The subsequently detached piece then split into large blocks which toppled forward one after the other in the direction of the fjord, so that finally large, clean ice slabs lay in front of the glacier terminus. The tilting ice blocks pushed the whole mass of fjord water, together with the ice debris which floated on it, in the direction of the sea. The tilting processes had terminated after approximately 8 min. Then a wave which had been reflected farther out in the fjord returned to the break-off zone, where it caused the formation of a large amount of ice debris and high jets of water.
Ice/Structure Interaction Tests with Ice Containing Flaws
Authors: Timco G.W.
Published: September 2017

A test series has been performed to investigate the influence of flaws or cracks in ice during an ice/structure interaction event. The tests were carried out by measuring the horizontal load on a 6 cm diamter vertical indentor which was being pushed through sheets of fresh-water ice containing flaws of various shapes, lengths, and densities. The results are analyzed and correlated in terms of an elementary damage theory. The tests show that flaws can have a significant influence on the load which an ice sheet can exert on a structure.
Snowfall and Oxygen-Isotope Variations off the North Coast of Ellesmere Island, N.W.T., Canada
Authors: Jeffries Martin O. , Roy Krouse H.
Published: September 2017

Snow-pack along the land-fast ice fringe off the north coast of Ellesmere Island was generally characterized by depth-hoar overlain by dense snow and wind slab. Mean snow depth in the study area was 0.54 m (1982-85) and the mean δ18O value of the snow-pack was -31.3˚/00. Isotope data were not obtained previously for this geographic region and, therefore, complement a previous study of δ18O variations in High Arctic snow (Koerner, 1979). The data are consistent with an Arctic Ocean moisture source. The δ18O profiles show seasonal variations, with winter snow being more depleted in 18O than fall and spring snow. However, the δ18O profiles are dominated by a trend to higher δ18O values with increasing depth. This is attributed to a decrease in δ18O values as condensation temperatures fall during the autumn-winter accumulation period. During this time, there is also a change from relatively open to almost complete ice cover in the Arctic Ocean. The change in evaporation conditions and consequent effect on δ values gives rise to a sharp discontinuity in the δ18O profiles and a bi-modal δ18O frequency distribution. The bi-modal distribution is reinforced by a secondary isotope fractionation that occurs during depth-hoar formation. This isotope effect leads to a wider δ18O range but does not significantly alter the mean δ18O value.