bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Model of Temperate Glacier Flow Applied to the Quiescent Phase of a Surge-Type Glacier
Authors: Bindschadler Robert
Published: September 2017

A time-dependent numerical model of temperate glacier flow without sliding is developed and applied to the quiescent phase of surge-type Variegated Glacier, Alaska. The model is based on a one-dimensional continuity equation but the transverse channel shape is explicitly included allowing the complex geometries of real glaciers to be modelled. Velocities and volume fluxes are calculated from the glacier geometry. Transverse stress is taken into account by shape factors which are fitted to measurements of geometry and velocity and are chosen to be insensitive to changes in geometry. Longitudinal stress gradients are taken into account by use of a large-scale surface slope. A Crank-Nicholson finite-difference approximation is used and it is unconditionally stable when a small contribution from the local slope is added to the average slope.

Model parameters are fitted to extensive data collected on Variegated Glacier in 1973 and 1974. Predictions of the model over a four year interval agree well with field measurements. Predictions of the current quiescent phase (1965–84) indicate depth increases in the upper glacier of more than 75 m with a twenty-fold increase in the volume flux. During this interval the base shear stress increases 40% in the upper glacier and decreases 20% in the lower glacier. During the mid to late quiescent phase, ice motion becomes more important than mass balance in the redistribution of mass over the central region of the glacier. If normal flow were to persist, the predicted steady-state profile would be an average of 100 m deeper and 41% more voluminous than in 1973.

The predicted base shear-stress gradient is never negative enough to satisfy Robin and Weertman’s (1973) condition for blockage of subglacial water flow. The annual rate of water production by dissipation of mechanical straining at the bed remains two orders of magnitude below that produced by summer surface melt. The predicted fractional increase in base stress during the quiescent phase is a maximum in the region believed to be the trigger zone of the surges.
Numerical Simulation of the Evolution of Ice Covers Using the Scandinavian and Laurentide Ice Sheets as Examples
Authors: Kvasov D. D. , Verbitsky M. Ya.
Published: September 2017

A non-linear parabolic equation describing the evolution of an isothermal linearly viscous ice sheet is numerically solved in non-dimensional coordinates obtained by normalization over the horizontal size of a glacier. The horizontal size of the ice sheet is defined from the solution of an ordinary differential equation, the integral mass balance. For simple climate models, approximate relations describing the evolution of glaciers are proposed. These relations and palaeogeographical data are used to estimate changes in the mass balance on the surface of the Scandinavian and Laurentide ice sheets during retreat of the last glaciation.
Antarctic Ice Sheet Surface Oxygen Isotope Values
Authors: Morgan V. I.
Published: September 2017

Collected data on the mean annual surface values for δ18O over Antarctica have been tabulated and also presented in map form. An additional map shows contours of constant δ18O values.
On the Secular Variation of Ice Flow Velocity at Lewis Glacier, Mount Kenya, Kenya
Authors: Hastenrath Stefan , Kruss Phillip
Published: September 2017

Measurements at various epochs in the course of the twentieth century indicate a slowing down of surface ice flow velocity. This is consistent with the numerical modeling of the secular glacier recession, which furthermore shows a gradual upward shift of the regions of highest velocity and mass flux. Crevasse orientation is transverse above, and longitudinal below, the velocity maximum. The secular change in the longitudinal velocity profile seems to affect the crevasse pattern. Net balance in the next five years is a major factor in future changes of the glacier. With this reservation, model calculations for a possible extreme scenario indicate a drastic overall velocity decrease, and a moderate further displacement of the velocity and mass-flux maxima up-glacier, by the mid 1980’s.
A Theoretical Model of Radiative Transfer in Young Sea Ice
Authors: Perovich Donald K. , Grenfell Thomas C.
Published: September 2017

A four stream discrete-ordinates photometric model including both anisotropic scattering and refraction at the boundaries is presented which treats the case of a floating ice slab. The effects of refraction and reflection on the redistribution of the incident radiation field as it enters the ice are examined in detail. Using one- and two-layer models, theoretical albedos and transmittances are compared to values measured in the laboratory for thin salt ice. With an experimentally determined three-parameter Henyey–Greenstein phase function, comparisons at 650 nm yield single-scattering albedos ranging from 0.95 to 0.9997. The models are then used to compare the effects of diffuse and direct-beam incident radiation, to investigate the dependence of spectral albedo and transmittance on ice thickness, and to determine the influence of very cold and melted surface layers.
The Pendular-Funicular Liquid Transition and Snow Metamorphism
Authors: Denoth A.
Published: September 2017

The influence of snow structure on the liquid water distribution is recorded by measuring the high-frequency relative permittivity. The structure is characterized by the size and the shape of the ice grains, which are derived by analyzing the static dielectric constant and by analyzing photographs of the surface of the snow samples. The liquid distribution is very sensitive to the liquid saturation and to the shape of the ice grains; it is unaffectcd by the grain size. A transition from the pendular into the funicular mode of liquid distribution occurs in the range of 7 to 18% saturation. This transitional zone is very sensitive to the structure of snow; it decreases from approximately 13 to 18% liquid saturation for new snow to 7 to 12% saturation for old, coarse-grained snow.
Glacier Outburst Floods From “Hazard Lake”, Yukon Territory, and the Problem of Flood Magnitude Prediction
Authors: Clarke Garry K. C.
Published: September 2017

In 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

As 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

Specimens 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

The 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

Shear 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

A 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

The “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

“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

Mount 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

Two 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

The 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

Many 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

A 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

The 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

Finite-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

A 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

Waves 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

Published 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

Most 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

The 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

The 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

A 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

The 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.
Determination of the Three-Dimensional Velocity Field in a Glacier
Authors: Raymond C.F.
Published: September 2017

A method for the determination of the three-dimensional velocity field in a glacier is described, Measurements in three or more bore holes arranged in an appropriate array are needed for its application. Surface motion measured by triangulation and tape measure, bore-hole profiles given by inclinometry, and the geometry of the bed are all considered simultaneously in order to determine the velocity field. The basic assumption is that velocity between the bore holes can be represented by suitable interpolation based on the measurements in the holes. Ice displacement parallel to bore holes is calculated indirectly from incompressibility and the constraint that velocity normal to the bed be zero. As an example, the method is applied to an array of 9 bore holes in Athabasca Glacier.
Basement Ice, Ward Hunt Ice Shelf, Ellesmere Island, Canada
Authors: Lyons J.B. , Savin S.M. , Tamburi A.J.
Published: September 2017

Oxygen-isotope and chlorinity determinations, as well as petrographie observations, indicate that the basement we of the Ward Hunt Ice Shelf is largely composed of a unique brackish ice, which interdigitates with sea ice. Some iced firn occurs near the top of the Basement Ice, below an unconformity.

stratification in brackish and sea ice represents annual increments to the bottom of the ice shelf The c-axis vertical orientation and small-angle grain-boundary relations in brackish ice are explained by nucleation and floating of ice dendrites from the undercooled brackish water zone to the bottom of the ice shelf, where they attach themselves sub-parallel to the plane of the undersurface.

Ice island T-3 did not come from a break-up of the main part of the Ward Hunt Ice Shelf, but probably originated in a nearby area to the west.
Albedo of Melting Sea Ice in the Southern Beaufort Sea
Authors: Langleben M.P.
Published: September 2017

Two Kipp hemispherical radiometers mounted back to back and suspended by an 18 m cable from a helicopter flying at an altitude of about 90 m were used to make measurements of incident and reflected short-wave radiation. The helicopter was brought to a hovering position at the instant of measurement to ensure that the radiometers were in the proper attitude and a photograph of the ice cover was taken at the same time. The observations were made in 1969 during 16 flights out of Tuktoyaktuk, Northwest Territories (lat. 69° 26’N., long. 133° 02’W.) over the fast ice extending 80 km north of Tuktoyaktuk. Values of albedo of the ice cover were found to decrease during the melting period according to the equation A = 0.59 —0.32P where P is the degree of puddling of the surface.
Instruments and Methods: A New Bore-Hole Inclinometer
Authors: Raymond C.F.
Published: September 2017

A newly developed bore-hole inclinometer permits the determination of bore-hole configurations with greater accuracy and efficiency in comparison with earlier systems of inclinometry. Instrument orientation is given to within 0.1° in magnitude of tilt and 10° in azimuth of tilt by an electrical output which can be read remotely from the surface.
An Improved Method for Determining Ice Fabrics
Authors: Hill J.R. , Lasca N.P.
Published: September 2017

In ice-fabric studies, use of an accessory plate is necessary in conjunction with the Rigsby universal stage to discriminate between the a- and c-axes of an ice crystal when the orientation of the c-axis is parallel or nearly parallel to the stage. The techniques described permit orientation of the c-axis regardless of its orientation.
A Hot-wire Engine to Produce Periodic Grooves on an Ice Surface
Authors: Tobin T.M. , Itagaki K.
Published: September 2017

A strain-tree grooving method has been developed for surface self-diffusion studies of ice. This method utilizes a hot-wire grooving engine and is capable of obtaining a uniform spacing between grooves ranging from 15.9 μm to 159 μm in increments of 15.9 μm.
Stress Variations with Ice Flow Over Undulations
Authors: Budd W.F.
Published: September 2017

The analysis of steady-state flow over bedrock perturbations of Budd(1970[a]) is extended to evaluate the stress variations associated with the flow. In particular the four separate terms of the fundamental one-dimensional (longitudinal) stress equation (Budd,1968) are examined to show explicitly how the longitudinal stress gradient G, the base stress τ, the surface slope stress s, and the integrated second derivative of the shear stress T all vary over-a given wave.

The result shows an error of a factor of 2 in some earlier studies relating longitudinal stress variations to the slope. This error resulted from the erroneous assumption that remains constant at its regional value. In fact the basal stress varies over the undulations in a similar way to the longitudinal stress gradient, and this is the same as the surface slope stress for long waves, but for short waves or less) requires the addition of the fourth term T, which then becomes dominant.
Small-Scale Strain Measurements on a Glacier Surface
Authors: Colbeck S. C. , Evans R. J.
Published: September 2017

Surface deformations in the neighborhood of a crevasse field were measured over short (3 m) gage lengths in order to study flow conditions associated with crevasse formation. The results obtained were unusual in that they were inconsistent with large-scale results found by previous workers. It was concluded that the presence of small-scale surface effects, such as fractures, pot-holes and healed crevasses give rise to small-scale deformation fields with large spatial and temporal variations and that there is a lower limit of gage length below which deformation measurements pertinent to regional (low phenomena cannot be made. This lower limit is apparently an order of magnitude greater than the spacing of the features which give rise to localized effects.
Chloride Segregation Along Grain Boundaries in Ice
Authors: Prodi F. , Nagamoto C.T.
Published: September 2017

A new technique for precisely detecting chlorides in ice has been developed. It is based on a microchemical contact reaction which takes place when a thin surface layer of ice melts through a membrane filter previously soaked in a concentrated solution of silver nitrate and dried. The silver chloride thus formed is reduced to metallic silver under ultra-violet light. The results on natural hailstones and laboratory doped ice show that foreign molecules are mainly segregated along the grain boundaries rather than being captured in the ice lattice.

The technique, which makes quantitative evaluations possible, appears promising in all experimental studies on natural ice (hailstones and sea ice) and on ice artificially grown in the laboratory (by accretion or by freezing of solutions).
Oxygen-Isotope Measurements on 1700 ± 300 Year Old Antarctic Ice
Authors: Hamilton Wayne L.
Published: September 2017

Values of δ18OSMOW measured on ice from 250 m depth at old “Byrd station”. Antarctica, averaged about A monotonie trend in values through the 16 cm long core piece suggested that part of an annual layer was represented. Snow accumulation in excess of 14.4 g cm-2 year-1 ca 1 700 years B.P. is indicated.
A First Simple Model for Periodically Self-Surging Glaciers
Authors: Budd W. F.
Published: September 2017

A two-dimensional model of glacier flow is presented which includes periodical surging as a natural phenomenon for a certain class of glaciers. The input consists of the bedrock and balance profiles along the glacier, together with the ice flow properties and a frictional lubrication factor. The basal stress is determined from the condition of gross equilibrium for the whole glacier, together with the distribution of the frictional lubrication from energy dissipation along the glacier.

The difference between the basal stress and the down-slope stress of the glaciers produces longitudinal strain-rates which determine the basal sliding velocity. Since the velocity is also involved in the frictional lubrication, feed-back develops between the basal stress and sliding velocity.

For a given lubrication factor, a critical stage can be reached for which the velocity becomes sufficiently high to lower the basal stress, enough to cause very high velocities to develop. The model thus gives rise to three classes of glaciers with two modes of flow.

“Ordinary” glaciers do not have sufficient mass flux, for the given bedrock profile, to go beyond the “slow mode” in which the basal stress and velocity increase together as the glacier builds up to steady state.

“Fast” glaciers have sufficient flux to remain continuously in the “fast mode” with high velocities and relatively low basal stress.

“Surging” glaciers have sufficient flux to reach the fast mode but not sufficient to maintain it, and thus develop a periodically oscillating state between the fast and slow modes with gradual build up and rapid drainage.

Sample results are presented for models of a typical large valley surging glacier and for a very high-speed surging glacier.
Temperature Measurements in a Temperate Glacier
Authors: Harrison W. D.
Published: September 2017

Temperatures have been measured at two sites in a temperate glacier (Blue Glacier, Washington, U.S.A.) to depths of 192 and 76 m. The accuracy, which varies between about 0.002 and 0.005 deg, is about an order of magnitude better than previously obtained. Except near the surface, temperatures vary linearly with depth but are in disagreement with the simplest model of a temperate glacier, being about 0.02 deg colder near the surface and 0.04 deg colder at 192 m depth.
A Measurement of Surface-Perpendicular Strain-Rate in a Glacier
Authors: Harrison W. D.
Published: September 2017

The surface-perpendicular component of velocity and strain-rate have been determined at one site in the ablation area of Blue Glacier, Washington, U.S.A., where the total depth is about 250 m. The strain-rate is near zero at the surface but increases with depth to about 4% a−1 at 175 m. The results were obtained with the help of a finite deformation theory from the measured stretch of cables frozen into the ice.
Investigation of Polar Snow Using Seismic Velocity Gradients
Authors: Robertson James D. , Bentley Charles R.
Published: September 2017

Compressional wave velocity gradients at 43 of 50 Antarctic traverse stations plot as sequences of straight lines on semilogarithmic graph paper. Intersections of the lines appear to correlate with depths at which the predominant metamorphic mechanism in polar snow changes. The seismie pattern supports a three-layer interpretation of snow densification. The base of the upper layer (8.4±12.3 m) corresponds to the “critical depth” of Anderson and Benson (1963) at which snow grains settle into a “random closepacked” arrangement. The base of the lower layer may correspond to the firn: ice transition depth, but more data are needed to confirm this conclusion. It is unclear what densification phenomenon is marked by the base of the middle layer (27.7±4.4 m). The distinction between the middle and lower layers tends to disappear and the velocity gradient at a fixed depth increases as mean annual accumulation decreases.
Radio Echo Sounding On Temperate Glaciers
Authors: Goodman R. H.
Published: September 2017

A high-resolution radio echo sounder operating at a frequency of 620 MHz has been developed for studies of temperate glaciers. Excellent spatial resolution is obtained through the use of a short pulse length (70 ns) and an antenna beam width of 5.2°. Large amounts of high-quality data may be rapidly collected since the sounder incorporates an automatic positioning system and an on-line computer. Real time analysis of the echoes facilitates the understanding of complex reflecting horizons observed in temperate glaciers.

Results obtained during field trials of the echo sounder on both the Wapta Icefield and Athabasca Glacier are given. Intraglacial structures which may be due to water levels within the ice have been detected.
Radio Echo Soundings and Ice-Temperature Measurements in a Surge-Type Glacier
Authors: Clarke G. K. C. , Goodman R. H.
Published: September 2017

Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier.
Radio Soundings On Trapridge Glacier, Yukon Territory,Canada
Authors: Goodman R. H. , Clarke G. K. C. , Jarvis G. T , Collins S. G. , Metcalfe Robert
Published: September 2017

As part of a program to study surge-type glaciers, a radar-depth survey, using a frequency of 620 MHz, has been made of Trapridge Glacier, Yukon Territory. Soundings were taken at 26 locations on the glacier surface and a maximum ice thickness of 143 m was measured. A rapid change in surface slope in the lower ablation region marks the boundary between active and stagnant ice and is suggestive of an “ice dam” or the water “collection zone” postulated by Robin and Weertman for surging glaciers.
Effect Of Inversion Winds On Topographic Detail And Mass Balance On Inland Ice Sheets
Authors: Whillans I. M.
Published: September 2017

Steady-state gravity flow of air (inversion wind) on sloping snow-covered ice sheets is analyzed for sensitivity to local topography. Topographic features of the order of a few kilometres or less in length are too small to affect the direction and speed of this air flow. Air flow on a longer scale should however conform cosely to topography. Surface roughness on ice sheets is consistent with these results. Features of length shorter than a few kilometers (drifts and sastrugi) are transient, but longer features (surface undulations) remain essentially unaltered for many years. On the longer scale, inversion wind speed and therefore the amount of drifting and blowing snow should vary with the surface slope even where slope changes by as little as 1/10%. Observed variations in surface mass balance (aceumulated snow) in upper Marie Byrd Land, Antarctica, support this hypothesis.

Snow drift and inversion winds thus constitute a feed-back mechanism on the form of ice sheets and some of the topographic detail, formerly attributed to ice-flow character alone, may be in large part due to this mechanism.
Wind Regimes And Heat Exchange On Glacier De Saint-Sorlin
Authors: Martin S.
Published: September 2017

During the summers of 1969 and 1970, we recorded in the ablation zone of the Glacier de St-Sorlin (Massif des Grandes Rousses, France) temperature, air moisture, and wind profiles, as well as the radiation balance and the daily ablation. Numerous profiles characterize a katabatic flow following the line of greatest slope, and there appears to be a correlation between the speed of the “glacier wind” and the corresponding temperature gradients. Computed according to Prandtl’s theory of turbulent transfers, the flux of sensible and latent heat added to the radiation flux leads to theoretical values for the daily melting in good agreement with the measured values. The relative importance of the radiation balance on the melting of the snow is 57%; that of the sensible heat flux is 43%; the latent heat flux is very weak and negative.
Water Flow in Glaciers: Jökulhlaups, Tunnels and Veins
Authors: Nye J. F.
Published: September 2017

The physics of water flow within and under glacier ice is examined with special reference to the periodic catastrophic outbursts of water (jökulhlaups) from the subglacial lake Grímsvötn, Vatnajökull, Iceland. The lake is sealed until it reaches a critical level which enables it to lift the glacier, helped by a hydrostatic cantilever effect. The differential equations for non-steady water flow in a subglacial tunnel are derived and applied to the 1972 Grímsvötn outburst. The discharge: time relation observed during the growth stage, and the abrupt ending of the flood, are both very well accounted for by a theory which is insensitive to the details of the subglacial tunnel system. The steady state, in which an intergranular vein or tunnel is simultaneously melted open by frictional heat and closed by plastic deformation, may be stable or unstable according to the conditions imposed at the ends. This explains why the flow of water in a vein does not normally increase unstably as in a jökulhlaup. An ice-dammed lake does not drain away through the vein system because the driving force on the vein-water is towards the lake rather than away from it.
The Application of Fracture Mechanics to the Problem of Crevasse Penetration
Authors: Smith R. A.
Published: September 2017

The elastic stress intensity factor is a parameter used in fracture mechanics to describe stress conditions in the vicinity of the tip of a sharp crack. By superimposing solutions of stress intensity factors for different loading conditions, equations are derived which model crevasses in ice. Solutions are presented for the theoretical depth of isolated crevasses, free from or partially filled with water. Close agreement exists with a previous calculation by Weertman using a different technique. The effect of crevasse spacing is investigated and it is demonstrated that closer spacing always reduces crevasse depth, but over a wide range of spacing the predicted variation in depth is slight.
The Bearing Capacity of Floating Ice Plates Subjected to Static or Quasi-Static Loads*
Authors: Kerr Arnold D.
Published: September 2017

This paper contains a critical survey of the literature on the bearing capacity of floating ice plates. It consists of a discussion of general questions, a critical survey of analytical attempts to determine the bearing capacity of floating ice plates and a survey of field and laboratory tests on floating ice plates and their relation to the analytical results. It concludes with a systematic summary of the results, a discussion of observed shortcomings, and suggestions for needed investigations.