bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for Headwall Weathering Zones, Boundary Glacier, Canadian Rocky Mountains
Authors: Gardner James S. 
Published: September 2017

AbstractTemperature records from several randkluft sites at the margins and headwall of Boundary Glacier (lat. 52° 12′ N., long. 117° 12′ W.) in the Canadian Rocky Mountains are presented. These records indicate that during the ablation season a diurnal freeze-thaw air and rock-surface temperature regime occurs in a 2 m wide zone centred on the randkluft lip. Deeper in the randkluft, stable sub-zero conditions prevail whereas above the randkluft an above-freezing temperature regime prevails. The freeze-thaw temperature regime, observed freezing of melt water and rain water on randkluft rock surfaces, and copious in-situ loose weathering products on the headwall and marginal free faces suggest an active frost-shattering environment. Down-slope migration of the randkluft lip during the ablation season results in a migration of the freeze-thaw zone and thus a seasonal extension of the rock surface area exposed to the favorable weathering environment. Longer-term glacier fluctuations, with attendant thinning and thickening of the ice body, could result in large areas of marginal and headwall rock surfaces being exposed to the randkluft weathering environment over long periods of time. The data and observations from Boundary Glacier support an idea, suggested by Battle (1960), that open and shallow randklufts, rather than closed and deep bergschrunds, are a focus of weathering at glacier margins and thus a potential factor in cirque development.
Research on the Tunnel Excavated In Urumqi Glacier No. 1, Tianshan Glaciological Station, China
Authors: Maohuan Huang , Zhongxiang Wang 
Published: September 2017

AbstractA tunnel was excavated in Urumqi Glacier No. 1, at the Tianshan Glaciological Station. Ice temperature, ice displacement, deformation, and basal sliding, etc. were observed at regular intervals. It is shown that the temperature near the glacier bed is close to the melting point and that the largest proportion of the overall glacier motion is within the lowermost ice layers. The glacier ice is in a state of compression. The maximum shear strain increases towards the entrance of the tunnel, corresponding to the change in slope of the ice surface, and also towards the bedrock.
Crystal Structure of Ice Accreted on an Ice Substrate
Authors: Nasello Olga B. , Levi Laura , Prodi Franco 
Published: September 2017

AbstractThin ice deposits, grown on a prismatic ice substrate and the first layers of large deposits grown about a cylindrical ice collector, are studied. Experiments were performed at 30 m s–1 wind speed and Ta near –20° C. Progressive structural changes in thin accretions with time of water-injection were observed, when the substrate temperature was Ts > –5°C. After 60s injection, which determined a deposit ~1 mm thick, the preferred orientation was established and the mean grain area was ~0.01 mm2. Such structural changes did not appear along the initial layers of thick deposits. These differed mainly from the subsequent zone because of the larger value of the preferred angle between the c-axis and the growth direction. These effects are discussed by considering the nucleation and orientation selection processes which occurred during droplet freezing and the annealing effects that occurred below the growth front. The different c-axis orientations in the initial and main zones are related to the different Ts values during their formation.
Paleothermometry by control methods
Authors: MacAyeal Douglas R. , Firestone John , Waddington Edwin 
Published: September 2017

AbstractThe recovery of past climatic conditions from ice-sheet borehole temperatures can best be accomplished using the calculus of variations (control methods) to minimize mismatch between the observed profile and a solution of the heat equation which depends on the unknown climate history. Here, we use control methods and a simple one-dimensional heat equation and the temperature depth profile observed at Dye-3 to infer the surface temperature of south Greenland over the last 30 000 years. This history illustrates the virtues that recommend control methods for future use in borehole-temperature analysis, namely: (i) it meets objective performance criteria, and (ii) its uncertainty can be established quantitatively. Our inferred climate history displays what may be the Younger Dryas cold event at about 9000 years BP. Borehole paleothermometry by control methods may thus resolve the controversy concerning the interpretation of Greenland ice-core isotope records.
Surficial glaciology of Jakobshavns Isbræ, West Greenland: Part I. Surface morphology
Authors: Echelmeyer K. , Clarke T. S. , Harrison W.D. 
Published: September 2017

AbstractJakobshavns Isbræ is a large, fast-moving ice stream/outlet glacier in West Greenland which ends at a floating, calving front. It drains about 6.5% of the area of the Greenland ice sheet. Studies of its surface morphology are described in this paper. The surface is relatively steep (0.01–0.03) and the thickness is large (up to 2600 m along the center line (Clarke and Echelmeyer, 1989)), indicating very high driving stresses (200–300 kPa). The ice stream is about 6 km wide and 85–90 km long, all of which is in an area of surface melting. The base of the ice stream, and of much of the drainage area, is below sea level. Marginal crevasse zones have a width on the order of the width of the ice stream itself. Unique surficial features are ice blisters and lakes; the latter have a sequence of ogive-like features on their floating ice cover which can be used to determine velocity. There is a pinning point near the terminus which may act as a stabilizing influence, possibly playing a role in halting, at least temporarily, a recent retreat of the terminus. Ice-thickness estimates at the terminus lead to a flux which is less than previously assumed by others (e.g. Bindschadler, 1984; Pelto and others, 1989) when estimating Jakobshavns Isbræ’s drainage basin to be nearly in balance.The driving stresses on Jakobshavns Isbræ are an order of magnitude higher than those of the ice streams of West Antarctica. Its crevasse patterns are much less localized. Its relatively unconfined terminus is more comparable to that of relatively unbuttressed ice streams such as Pine Island and Thwaites Glaciers than it is to other West Antarctic ice streams which terminate in large, confined ice shelves.
On the Role of Mechanical Energy in Maintaining Subglacial Water Conduits at Atmospheric Pressure
Authors: Hooke Roger Leb. 
Published: September 2017

AbstractRecent theoretical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady-state conditions. This, however, is not necessarily the case. Where discharges are larger than a few tens of liters per second and the down-glacier slope of the bed is more than a few degrees, the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice. As a result, the pressure in such tunnels may normally be atmospheric, or possibly even at the triple-point pressure if there is no open connection to the glacier surface. Simple calculations suggest that such pressures in subglacial conduits may be more common than heretofore anticipated.The positions of such “open” conduits may be unstable to small perturbations in discharge or ice velocity. This is because the mechanical energy available in excess of that needed to balance closure can instead offset the general flow of the ice. Conduits can thus trend diagonally across the direction of ice flow. If an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of the conduit, more mechanical energy will become available, resulting in a positive feedback process.Subglacial channels at atmospheric pressure may influence the origin and morphology of certain glacial landforms, such as eskers and “plastically-molded” features.
A Procedure for Testing Polycrystalline Ice in Uniaxial Tension
Authors: Lee R. W. , Currier J. H. , Lim P. N. , Schulson E. M. 
Published: September 2017

AbstractA procedure is described for testing ice in tension. It incorporates a one-piece lucite mold, two carpeted “Synthane” end-caps and a pair of yokes anti ball joints. Use of the procedure has resulted in a successful test rate greater than 80%.
Thin Sectioning and Surface Replication of Ice at Low Temperature
Authors: Daley Margaret A. , Kirby Stephen H. 
Published: September 2017

AbstractWe have developed a new technique for making thin sections and surface replicas of ice at temperatures well below 273 K. Cyanoacrylate glue forms a strong bond with ice and glass at 245 K, eliminating the need to fix the sample to the thin-section slide by melting and freezing. Surface replicas are made by melting away sample material once the glue has cured. Glue replicas are permanent and highly detailed, making them suitable for microstructural and textural studies at room temperature. Thin sections glued with cyanoacrylate glue are comparable in quality to melted-on sections. The ability to make thin sections without melting sample material is important in textural and microstructural studies of ice deformed at low temperatures because of annealing effects we have observed during conventional section making.
Milne Glacier, Northern Ellesmere Island, N.W.T., Canada: a Surging Glacier?
Authors: Jeffries Martin O. 
Published: September 2017

AbstractDuring the period 1966 to 1983 Milne Glacier advanced 4.25 km at a mean annual rate of 250 m a−1. Since surges commonly occur over a two or three year period the maximum rate of advance could have been greater than 2 km a−1. The glacier terminus has a number of features indicative of past surge behaviour. Of these, at least three looped moraines suggest surges of the main valley glacier and tributary glaciers. As Milne Glacier is a cold glacier, surges may possibly be thermally regulated Accumulation rates on the ice caps of northern Ellesmere Island are low hence a critical condition in the “reservoir area” will be only slowly attained. As a consequence the periodicity of surges in Milne Glacier and other High Arctic glaciers is expected to be high.
Air Permeability as a Textural Indicator of Snow
Authors: Conway H. , Abrahamson J. 
Published: September 2017

AbstractTwo air-permeability devices were developed and measurements were made to study the relationship between air permeability and structure of different snow types. Permeabilities varied both with position and direction in the snow-pack, and changed with time as metamorphic changes occurred. A marked increase of air permeability was noted as faceted crystals grew due to radiation recrystallization. In other observations, as a snow-pack densified and crystals became more rounded (destructive metamorphism) the air permeability decreased. Measurements were made of air permeability of snows that had been subjected to a creeping tensile strain, and initial tests indicated that the changes in air permeability due to strain, even to rupture, were significant, but small compared with the intrinsic variability of snow.
A Glacier Flow Model Incorporating Longitudinal Deviatoric Stresses
Authors: Shoemaker E. M. , Morland L. W. 
Published: September 2017

AbstractA model for glacier flow is developed which incorporates longitudinal deviatoric stress contributions to the field equations. The underlying assumptions may be applied to develop models for various situations. Here, they are developed for steady-state and non-steady-state sliding glaciers in plane flow. The models reduce to a proper generalization of plane-flow pseudo-hydrostatic theory if longitudinal deviatoric stresses are neglected in comparison to basal shear stresses. Solution of this simpler reduced model allows an estimate to be made of the magnitude of the longitudinal deviatoric stress to test if it is negligible or, more generally, investigate under what conditions it can be neglected. The steady-state model predicts that longitudinal deviatoric stresses are negligible for very arbitrary non-uniform sliding-law distributions provided that the following conditions exist: the region must be distant from an ice divide or terminus and subject to normal (not extreme) accumulation or ablation. On the other hand, examples are produced where, under non-steady conditions, longitudinal deviatoric stresses are important and even dominant.
Flood and Landslide Events, Peyto Glacier Terminus, Alberta, Canada, 11–14 July 1983
Authors: Johnson P. G. , Power J. M. 
Published: September 2017

AbstractTwo flood waves from the terminus of Peyto Glacier occurred as a result of very high precipitation in early July 1983 and a landslide which exposed a large section of ice-cored moraine. The flood waves induced erosion, and subsequent melt, of the moraine and deposited an estimated 6000 m3 of gravel in the valley. The majority of the deposition occurred in an area approximately 200 m × 20 m to depths of 3 m at the site of the National Hydrology Research Institute gauging station 1 km from the glacier terminus. The initial flood washed away most of the equipment from the site and the gravel deposition totally destroyed the rest of the installation. These events appear to be unique in the period that hydrological records have been maintained for Peyto Creek.
The Dynamics of Ice-Sheet Outlets
Authors: Mcintyre N. F. 
Published: September 2017

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.
Adjusting Two-Dimensional Velocity Data to Obey Continuity
Authors: Rasmussen L. A. 
Published: September 2017

AbstractAn algorithm is developed for adjusting glacier surface-velocity vectors, given on the nodes of a square grid, so that they obey a central-difference approximation of the continuity equation. Also required on the grid nodes are the glacier thickness, the ratio of the surface-velocity to the average velocity in the column, and the difference between the mass balance and the thickness change. All these other variables are assumed to be known exactly, and only the surface-velocity field is adjusted. The result is optimum in the sense that the magnitude of the adjustment is minimized. Either the relative or the absolute adjustment can be minimized, depending on how weights are specified. No restriction is placed on the shape of the solution region, and no boundary condition is required. The algorithm is not iterative. The algorithm first forms a parallel flow field that satisfies the continuity equation, and then uses a stream function to add a divergenceless field to it. The stream function that leads to the minimum velocity adjustment is obtained as four independent, interlacing solutions covering the solution region. For each of the four, a well-conditioned, sparse-matrix system of simultaneous linear equations is solved. A compact, sub-optimum, well-behaved iterative procedure is also developed for transforming part of the velocity adjustment into an adjustment of the thickness field.
Growth Forms of Large Frost Crystals in the Antarctic
Authors: Knight C. A. , Devries A. L. 
Published: September 2017

AbstractA variety of frost-crystal forms found growing from the vapor in ice caves and tunnels in the Antarctic are described and illustrated. Complex layered structures found within large, skeletal crystals are ascribed to the action of the temperature gradient. Some novel c-axis growth forms and a rare type of bicrystal growth – accelerated growth in a particular direction along a particular grain boundary – are also shown.
Calculation of A Velocity Distribution from Particle Trajectory End-Points
Authors: Rasmussen L. A. R 
Published: September 2017

AbstractThe longitudinal component of the velocity of a particle at or near a glacier surface is considered, its position as a function of time being termed its trajectory. Functional relationships are derived for obtaining the trajectory from the spatial distribution of velocity and for obtaining the velocity distribution from the trajectory. It is established that the trajectory end-points impose only an integral condition on the velocity distribution, and that no individual point on the velocity distribution can be determined if only the end-points are known. An example is given of a deduced velocity distribution that is consistent with (although not uniquely determined by) the end-points of several trajectories on the lower reach of Columbia Glacier, Alaska. It is shown that constructing a velocity distribution by assigning the average trajectory velocity to the trajectory mid-point can be subject to errors of several per cent for velocity distribution features that are typical of actual glaciers. The error in this method is determined, and closed-form expressions for the trajectory are obtained, for linear velocity distributions and for two classes of second-degree distributions. The class of functions is identified to which the velocity distribution must belong for this error to be zero.
Modifications to the Theory of Intraglacial Waterways for the Case of Subglacial Ones
Authors: Lliboutry Louis 
Published: September 2017

AbstractIt is argued that in temperate mountain glaciers, waterways are subglacial. It is shown that the theory of Spring and Hutter (1981) for intraglacial flooded conduits leads to an equation for the grade line which differs from Röthlisberger’s (1972) only by negligible terms, and a slight modification of the exponent of the discharge. For a subglacial flooded waterway two important processes should instead be introduced: the enhancement of plastic deformation on the up-stream side of bumps, and the heat afforded by ground water (which in winter accounts for most of the discharge). The theory modified in this way explains why Röthlisberger had to adopt an unrealistic value for the rheological parameter of ice. It leads to the conclusion that in areas which are not overdeepened, most of the year subglacial waterways should remain not flooded and at atmospheric pressure. The case of overdeepening is examined. Finally the implications of this new model for glacier sliding theory are demonstrated.
Dual Frequency Radar Ice and Snow Signatures
Authors: Ketchum R. D. 
Published: September 2017

AbstractDual frequency (X-band and L-band) synthetic-aperture radar imagery of sea ice is examined to show the differences between the bands and their complementary nature for resolving ambiguities in interpretation. High backscatter at X-band from visibly smooth thin ice is not observed at L-band. One hypothesis is that the high X-band backscatter may be caused by a reflective layer at the snow/ice interface. A second hypothesis is that the high X-band backscatter may be caused by moisture in the snow. A third hypothesis states that the phenomenon may be due to snow flowers. High backscatter at L-band is observed for slush on open water. The return is very weak at X-band, thus allowing distinction of slush by comparing L-band and X-band images. High intensity, but only partial returns from icebergs at L-band have been observed. The hypothesis is that internal iceberg/sea-water reflections are occurring. Some signals are directed away from the antenna, other reinforced signals are returned, producing very bright images. Occasionally, time-delayed signals are returned causing a false image at far range from the iceberg. The conclusion is that L-band is a poor choice for studies of iceberg distribution and size, but a good choice for iceberg detection because of the high reinforced returns from many icebergs and the low return from the adjacent sea ice. The penetration and subsequent signal loss of L-band in glacial ice, when compared to high X-band returns, may be useful to map glacierized land masses.
Optical Measurements of Water Lenses in Ice
Authors: Walford M.E.R. , Roberts D.W. , Hill I. 
Published: September 2017

AbstractThe dihedral angle of water at a grain boundary in ice is found, by measuring the optical focal length of lenticular water inclusions, to be 33.6 ± 0.7°. The new result leads to only minor revision of published experimental values of specific surface free energies in the ice–water system (Ketcham and Hobbs, 1969).
Interpretation of Radio-Echo Returns from Internal Water Bodies in Variegated Glacier, Alaska, U.S.A.
Authors: Jacobel Robert W. , Anderson Stefan K. 
Published: September 2017

AbstractRadio echo-sounding studies were used to detect water-filled cavities on Variegated Glacier, Alaska, during its surge in 1983. Cavity locations were determined by spatial surveys, and changes in cavity size and water content over a 5 week period were inferred from phase and amplitude changes in the echo wave form. Data were taken at both 4 and 8 MHz central frequencies of the impulse transmitter. These bi-frequency results, together with spectral analysis of the digitized wave forms, were used to provide additional information about the cavity dimensions. Cavity response is interpreted in terms of a simplified model of a thin layer of strong dielectric contrast. Computer simulations of radar pulses encountering such layers reproduce the main features of the data.