bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glacier Outburst Floods From “Hazard Lake”, Yukon Territory, and the Problem of Flood Magnitude Prediction
Authors: Clarke Garry K. C. 
Published: September 2017

AbstractIn August 1978 “Hazard Lake” released 19.62 × 106 m3 of water through a subglacial tunnel beneath Steele Glacier, Yukon Territory, Canada. The discharge during the outburst flood was measured by recording lake level changes with time, and a peak discharge of approximately 640 m3 s–1 was estimated from the data. We have attempted to model the 1978 flood from “Hazard Lake” using an adaptation of Nye’s (1976) theoretical model for jökulhlaups from Grimsvötn. Our aim has been to calibrate the Nye model as a first step toward using it as a peak discharge estimator for other glacier–dammed basins. The agreement between our measured and simulated hydrographs is good, and we find that creep closure, though included in our analysis, appears to play an insignificant role in limiting the discharge of “Hazard Lake”. Release of thermal energy from the relatively warm lake water is the dominant factor contributing to tunnel enlargement.The Manning roughness of outlet channels from glacier–dammed lakes is not known a priori and must either be assumed or estimated after the fact from the flood hydrograph. For “Hazard Lake” our fit implies Manning roughness in the range n′ = 0.105 m–1⁄3 s, consistent with Nye’s estimate of n′ = 0.12 ml⁄3s for the 1972 Grimsvötn flood and our estimate of n′ = 0.12 m1/3 s for the 1967 Summit Lake flood. If the Manning roughness for flood conduits can be shown to lie within a narrow range, this would constrain one of the least certain variables of the Nye model.By making several simplifying assumptions, we have succeeded in reducing our adapted version of Nye’s model to a simple mathematical description involving dimensionless numbers characterizing reservoir geometry and the relative magnitudes of creep closure and tunnel enlargement by melting. In this simplified form, the influence of lake temperature, reservoir geometry, and creep closure on the character of flood hydrographs can be conveniently studied.
Oxygen-Isotope and Total Beta-Radioactivity Measurements on 10 m Ice Cores from the Antarctic Peninsula
Authors: Peel D. A. , Clausen H. B. 
Published: September 2017

AbstractAs part of the Glaciology of the Antarctic Peninsula (GAP) programme, the snow cover at 25 stations was sampled to 10 m depth for oxygen–isotope and total β-radioactivity analysis. The mean annual oxygen–isotope ratio correlates satisfactorily with 10 m temperature despite the complex topography of the area and suggests on average that climatic trends in the region are fairly systematic. The relationship with temperature is similar to that derived from a simple model in which an air mass initially of maritime subtropical characteristics is progressively cooled as it moves towards the region. The detailed isotope profiles show that for future deep drilling the most easily interpretable climatic information will be found in the more continental areas—on the cast coast and on the plateau in the south of the region. The degree of continentality of particular sites is reflected in the amplitude of the annual wave in the upper portion of the isotope ratio profile as well as in the accumulation rate.
Steady-State Preferred Orientation of Ice Deformed in Plane Strain at –1°C
Authors: Wilson C. J. L. , Russell-Head D. S. 
Published: September 2017

AbstractSpecimens of polycrystalline ice were experimentally deformed in plane strain at a temperature of –1°C, under a constant load and with shortening strains varying from 2 to 27%. The random c-axis orientation of the initial ice aggregates changes continuously with increasing strain towards a steady-state, small-circle containing two maxima lying about the shortening direction. The ice microstructure is sequentially transformed from undeformed grains to smaller, irregular, deformed grains containing recrystallized grains. Grain growth then occurs forming a coarse interlocking-grain aggregate. These microstructural changes are attributed to solid-state processes occurring during deformation. The previously deformed specimens were then annealed without a load at –1°C. Annealing resulted in a substantial grain-size coarsening. However, no c-axis preferred-orientation difference developed between annealed and unannealed samples.
Inversion for Physical Characteristics of Snow using Passive Radiometric Observations
Authors: Rotman S. R. , Fisher A. D. , Staelin D. H. 
Published: September 2017

AbstractThe Nimbus-6 Satellite’s Scanning Microwave Spectrometer (SCAMS) mapped the terrestrial surface continuously for eleven months at 22.2 and 31.6 GHz. A semi-empirical method was devised to process these observations of Greenland and Antarctica and to infer long-term snow accumulation rates; comparison with in situ data suggests the method is generally successful except in certain locations where re-melting is more likely.
Shear Test on Snow Explained by Fast Metamorphism
Authors: Montmollin Vincent de 
Published: September 2017

AbstractShear tests performed on natural snow exhibited three kinds of behaviour with increasing shear rate: (1) viscous, without failure, (2) brittle of the first kind (cycles of brittle failure), (3) brittle of the second kind (only one brittle failure, and solid friction). These results can be explained by fast metamorphism of the bond system during the tests. When the shear rate is low, bonds can be regenerated after their destruction, and this regeneration is less active as the shear rate increases.
Further Results on Studies of Temperature-Gradient Metamorphism
Authors: Adams E. E. , Brown R.L. 
Published: September 2017

AbstractA correlation between temperature gradient in snow–pack and material strength is found to exist in laboratory studies on temperature gradient metamorphism of snow. These results are in agreement with earlier field investigations and eliminate diurnal solar and temperature variations as reasons for the existence of the maximum temperature gradient in the zone of minimum strength. Also the laboratory studies have indicated that locally dense layers such as ice crusts tend to enhance weakness directly below the crust due to local alteration of the thermal regimen. Further studies are continuing to describe the thermodynamic process of temperature gradient metamorphism more exactly.
Stress-gradient Coupling in Glacier Flow: IV. Effects of the “T” Term
Authors: Kamb Barclay , Echelmeyer Keith A. 
Published: September 2017

AbstractThe “T term” in the longitudinal stress-equilibrium equation for glacier mechanics, a double y-integral of ∂2τxy/∂x2 where x is a longitudinal coordinate and y is roughly normal to the ice surface, can be evaluated within the framework of longitudinal flow-coupling theory by linking the local shear stress τxy at any depth to the local shear stress τB at the base, which is determined by the theory. This approach leads to a modified longitudinal flow-coupling equation, in which the modifications deriving from the T term are as follows: 1. The longitudinal coupling length is increased by about 5%. 2. The asymmetry parameter σ is altered by a variable but small amount depending on longitudinal gradients in ice thickness h and surface slope α. 3. There is a significant direct modification of the influence of local h and α on flow, which represents a distinct “driving force” in glacier mechanics, whose origin is in pressure gradients linked to stress gradients of the type ∂τxy/∂x. For longitudinal variations in h, the “T force” varies as d2h/dx2 and results in an in-phase enhancement of the flow response to the variations in h, describable (for sinusoidal variations) by a wavelength-dependent enhancement factor. For longitudinal variations in α, the “force” varies as dα/dx and gives a phase-shifted flow response. Although the “T force” is not negligible, its actual effect on τB and on ice flow proves to be small, because it is attenuated by longitudinal stress coupling. The greatest effect is at shortest wavelengths (λ 2.5h), where the flow response to variations in h does not tend to zero as it would otherwise do because of longitudinal coupling, but instead, because of the effect of the “T force”, tends to a response about 4% of what would occur in the absence of longitudinal coupling. If an effect of this small size can be considered negligible, then the influence of the T term can be disregarded. It is then unnecessary to distinguish in glacier mechanics between two length scales for longitudinal averaging of τb, one over which the T term is negligible and one over which it is not.Longitudinal flow-coupling theory also provides a basis for evaluating the additional datum-state effects of the T term on the flow perturbations Δu that result from perturbations Δh and Δα from a datum state with longitudinal stress gradients. Although there are many small effects at the ~1% level, none of them seems to stand out significantly, and at the 10% level all can be neglected.The foregoing conclusions apply for long wavelengths λh. For short wavelengths (λ h), effects of the T term become important in longitudinal coupling, as will be shown in a later paper in this series.
Medial Moraines and Surface Melt on Glaciers of the Torngat Mountains, Northern Labrador, Canada
Authors: Rogerson R.J. , Olson M.E. , Branson D. 
Published: September 2017

Abstract“Avalanche-type” medial moraines are described on four Torngat Mountains glaciers with single, rather than compound, firn basins. They form from debris avalanching down couloirs and are exposed by ice melt to form extensive debris covers on glacier snouts in the Torngat Mountains. The debris may play an important part in helping the glacier survive periods with warm summers and/or dry winters since, in the Torngat Mountains, average ice melt on debris-covered sites is approximately one-third that on exposed ice.
Effects of the 1966–68 Eruptions of Mount Redoubt on the Flow of Drift Glacier, Alaska, U.S.A.
Authors: Sturm Matthew , Benson Carl , MacKeith Peter 
Published: September 2017

AbstractMount Redoubt, a volcano located west of Cook Inlet in Alaska, erupted from 1966 to 1968. This eruptive cycle removed about 6 × 107 m3 of glacier ice from the upper part of Drift Glacier and decoupled it from the lower part during a sequence of jökulhlaups which originated in the Summit Crater and flooded Drift River. The same events blanketed the lower part of the glacier with sand and ash, reducing ice ablation. Normal snowfall, augmented by intense avalanching, regenerated the upper part of the glacier by 1976, 8 years after the eruptions. When the regenerated glacier connected with the rest of Drift Glacier, it triggered a kinematic wave of thickening ice accompanied by accelerating surface velocities in the lower part of the glacier. Surface velocities increased by an order of magnitude and were accompanied by thickening of 70 m or more. At the same time, parts of the upper glacier thinned 70 m. The glacier appears to be returning to its pre-eruption equilibrium condition.
Implications of the form of the Flow Law for Vertical Velocity and Age–Depth Profiles in Polar Ice
Authors: Wolff E.W. , Doake C.S.M. 
Published: September 2017

AbstractTwo situations are studied in relation to the flow law of polar ice. In each case, models are used with a flow-law exponent of one, and with the more traditional exponent of three. The horizontal velocity profile at Devon Island, Arctic Canada, is better fitted by n = 1; for the vertical velocity profile, n = 3 gives a better fit, but both model profiles fall well within experimental error. For the Camp Century age–depth profile, only n = 1 gives an acceptable fit when temperature is allowed for. The large discrepancy between isothermal and non-isothermal models for n = 3 shows the importance of allowing for temperature in studies of ice-sheet properties.
Three-Dimensional Coordination Number from Two-Dimensional Measurements: A New Method
Authors: Alley Richard B. 
Published: September 2017

AbstractThe average three-dimensional coordination number, n3, is an important measure of firn structure. The value of n3 can be estimated from n2, the average measured two-dimensional coordination number, and from a function, Γ, that depends only on the ratio of average bond radius to grain radius in the sample. This method is easy to apply and does not require the use of unknown shape factors or tunable parameters.
Grain Growth in Polar Ice: I. Theory
Authors: Alley R. B. , Perepezko J.H. , Bentley C.R. 
Published: September 2017

AbstractMany observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood. Here we develop the theory of grain growth in ice that is not deforming rapidly, and in the succeeding paper we use this theory to explain observations from glacial ice. In the absence of significant strain energy, the driving force for grain growth arises from grain-boundary curvature. Grain growth is slowed by the interaction of grain boundaries with extrinsic materials (microparticles, bubbles, and dissolved impurities). If the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material, then the grain-boundary velocity is determined by the velocity characteristic of the extrinsic material (low-velocity regime). If the driving force is large enough to cause separation, then boundaries migrate more rapidly than the extrinsic material (high-velocity regime) but the net driving force is reduced through transient pinning by the extrinsic material. Polar ice is typically in the low-velocity regime relative to dissolved impurities and the high-velocity regime relative to microparticles and bubbles. Cross-sectional area of grains is predicted to increase linearly with time under most but not all circumstances.
The Granular Structure of Snow: An Internal-State Variable Approach
Authors: Hansen A. C. , Brown R. L. 
Published: September 2017

AbstractA statistical model characterizing the granular structure of snow is developed using quantitative stereology. The model is based on specific parameters (e.g. bond radius, grain-size, etc.) which take the form of internal-state variables in a constitutive theory for high-rate deformation of snow. In addition to parameters developed by other authors in previous investigations, a new parameter characterizing the mean bond length is developed. More significantly, general relations are derived for the mean number of bonds per grain and mean number of grains per unit volume without making any assumptions regarding the shape or size of the ice grains, or their respective distributions.
Mass-Balance Measurements: Problems and two New Methods of Determining Variations
Authors: Reynaud Louis , Vallon Michel , Letreguilly Anne 
Published: September 2017

AbstractThe optimum continuation of series of mass-balance measurements and their extension to unmonitored glaciers are important problems in contemporary glaciology. For this purpose, two new practical survey methods are proposed, based on the linear-balance variations model of Lliboutry (1974). The first method is a simplified application of the linear model that uses only a data set limited to selected fixed-measurement sites. It was developed to obtain the mass-balance variation in cases where data are too scarce to obtain the global mass balance or to apply the Lliboutry algorithm. This simplified linear model is used with the 8 years’ of surveys on glacier d’Argentière. The second method uses the continuity equation to derive the mass balance of a glacier sector delimited by two cross-profiles where the surface velocities, surface altitudes, and depths are known. By using this continuity method, the entire mass-balance series is established for a sector of glacier de Gébroulaz (Vanoise area, France) from 1908 to 1950, as well as for two sectors of Unteraargletscher (Oberland, Switzerland) from 1924 to 1981.
Finite-Element Simulation of the Thermal Regime of the Erebus Glacier Tongue, Antarctica
Authors: Stolle D.F.E. , Mirza F.A. 
Published: September 2017

AbstractFinite-element method is used to determine the temperature distribution within the Erebus Glacier tongue based on information from short-term observations (Holdsworth, 1982). It is shown that, provided the up-stream temperature profile along the depth is known, steady-state assumptions are reliable for computing the temperature field within most of the ice mass at any given time for a glacier tongue. Numerical results from analyses of the Erebus Glacier tongue also indicate that the main transport of heat is through advection as expected and, hence, a realistic estimate of the velocity field becomes important.
A Procedure for Testing Cored Ice Under Uniaxial Tension
Authors: Lee Russell W. 
Published: September 2017

AbstractA procedure is described for testing cored ice specimens under uniaxial tension. The procedure incorporates an end-capping system described by Cole and others (1985), two carpeted Synthane end caps, and extensometers mounted directly on the ice. Use of the procedure has resulted in a successful test rate of 75%
Ice Pyramids on Glaciers
Authors: Fisher Joel E. 
Published: September 2017

AbstractWaves of ice on the Gorner Glacier (Switzerland) are described. These finally assume an appearance very similar to the ice pyramids of the Himalaya. The author shows that the former originate as avalanche snow which remains above the general surface of the glacier through its lightness and greater resistance to ablation than the denser glacier ice, and suggests, as do Visser and others, that some Himalayan ice pyramids also originate as avalanche snow.
Franz Josef and Other Glaciers of the Southern Alps, New Zealand
Authors: Suggate R. P. 
Published: September 2017

AbstractPublished literature on the glaciers of the Southern Alps, New Zealand, and the Franz Josef Glacier in particular, is reviewed under the headings of (1) rates of movement, and (2) evidences of advance and retreat. Comparison of available rainfall statistics with the dates of advance and retreat of this glacier suggests that advances are due to periods of high precipitation, and retreats to periods of low precipitation, the effects being seen at the terminal face about five years after such periods began.
Variations in Solar Radiation and the Cause of Ice Ages
Authors: Hoyle F. , Lyttleton R. A. 
Published: September 2017

AbstractMost astronomical hypotheses on the causes of ice ages are dynamically untenable. Alterations in the amount of solar radiation, however, have long been recognized as a possible cause, but only with recent progress in the theory of stellar evolution has it become clear that such changes must occur. At irregular intervals the sun will pass, and will have passed, with low relative speeds through interstellar hydrogen clouds, and the gravitational action of the sun leads to an increase in the quantity of material falling to the surface with high velocity. The conversion of the kinetic energy of fall of this material results in an increase of emission at the solar surface. Increases of order up to about 10 per cent of the present total radiation could occur, and the process is such that the extra energy would be located mainly in the shorter wavelengths.
The Origin of Dirt Cones on Glaciers
Authors: Swithinbank Charles 
Published: September 2017

AbstractThe characteristics and probable development of dirt cones on Vatnajökull (Iceland) are described. Thick accumulations of debris protect the ice beneath them from ablation, whereas thin ones accelerate the process. Under given conditions of ablation, the nature of the debris covering is the deciding factor—in particular its radiation absorption coefficient, conductivity and thickness. Contrasts are noted between the dirt cones of Vatnajökull and those of other glaciers. The nature of the debris and of the ablation varies greatly from place to place, but all dirt cones result from differential ablation.
On The Temperature Profile and the Age Profile in the Central Part of Cold Ice Sheets
Authors: Philberth K. , Federer B. 
Published: September 2017

AbstractThe generalized Glen’s law έ = έ0Tn exp (kθ ) is used to calculate die horizontal and vertical velocity profiles and from these the temperature and age profiles of cold ice sheets. It is shown that, by substituting for θ a function increasing linearly with height, velocity profiles for all ice sheets are obtained which represent excellent approximations to the true ones, since, above a critical height he where the deviation from linearity becomes large, the influence of temperature on ice flow becomes negligible. In a comparison of the present theory with Robin’s (1955) treatment a larger temperature difference ΔT of up to 30% is obtained. Furthermore the present theory yields an age considerably increased compared with Nye’s model; e.g. more than 50% at a relative height of h\H = 0·1.
Permeability, Brine Content and Temperature of Temperate Ice
Authors: Lliboutry L. 
Published: September 2017

AbstractA temperate glacier is defined as a glacier containing liquid inclusions in which the concentration of salts is not too high. Nevertheless these salts suffice to produce a depression in temperature comparable with that due 10 the pressure, and much greater than that due to interfacial energies. Because of this a large part of the liquid water present in the ice is not mobile, contrary to the theory of Nye and Frank. Deformation and recrystallization is bound to close off capillary intergranular channels, for glacier ice is usually impermeable. An explanation is given of why firn, at a depth which the annual cold wave does not reach, is nevertheless transformed relatively suddenly into practically impermeable ice. Saline inclusions will migrate with a velocity inversely proportional to the potential temperature (difference from the melting point of pure ice at the pressure in question) and proportional to the gradient of this potential temperature. This velocity, the salinity, the liquid water content, and the ice temperature, parameters which are all functions of the depth, are calculated for a steady state in a stagnant or moving glacier. Under the action of anisotropic stresses, isolated inclusions perpendicular to the maximum compressive stress will enlarge at the expense of their neighbours. If however the two inclusions are connected by a capillary channel, no enlargement occurs, but instead the salt content decreases, evacuated to the other inclusion. This process would constitute an objection to the theory of glacier sliding by melting and refreezing around small obstacles, unless new subglacial mechanisms were to occur.
Shear Stress at the Base of a Rigidly Rotating Cirque Glacier
Authors: Weertman J. 
Published: September 2017

AbstractThe value of the basal shear stress is derived for two-dimensional and three-dimensional cirque glaciers. It is assumed that a cirque glacier moves primarily by a rigid-body rotation over a bed of cylindrical or spherical shape. In the region of maximum ice thickness the new value of the basal shear stress is only about one half that derived from equations in common use in the literature. The new expression for the basal shear stress of a cirque glacier is used to correct a data point in Paterson’s recent compilation of measured sliding velocities and basal shear stresses of glaciers.