bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural-Hazard Maps for Land-Use Planning in Norway
Authors: Hestnes E. , Lied K.
Published: September 2017

Problems concerning natural-hazard mapping have been discussed by the Norges Geotekniske Institutt in pilot projects sponsored by the National Fund for Natural Disaster Assistance. Hazard-registration maps, geomorphic hazard maps and hazard-zoning maps are defined. Hazard-zoning maps are preferable in land-use planning. Both survey maps (1 : 50000) and detailed maps (1:5000) are of interest. A survey map (c. 600 km2) would be mainly based on airphoto interpretation and could be prepared in about 150 h. Detailed mapping is more time consuming and should be limited to development areas.

Mapping of “marine deposits” and “other areas” are handled by separate groups, mainly because of differences in technical and professional problems. This gives rise to two parallel series of survey maps and detailed maps.

The proposed programmes for survey mapping states that 80% of the marine areas should be evaluated in 5 years (1980-84), and that one-third of the country should be examined for rockfalls, rock slides, and snow avalanches in 10 years. Other hazard types are impossible to identify by survey mapping. There is a rising demand for detailed maps but as yet there has been no research project to standardize methods.

The hazard maps are intended primarily to be an aid in land-use planning.
Vertical profile and Horizontal Increase of Drift-Snow Transport
Authors: Takeuchi Masao
Published: September 2017

There are a number of published empirical formulae for drift-snow transport as a function of wind velocity. Comparing these formulae at the same wind velocity, however, results in considerable disagreement. It is hypothesized that the disparity arises from snow conditions and the various stages of development of drifting snow.

The horizontal distribution of drift flux was measured with snow traps along a transect parallel with the wind, beginning at an up-wind boundary that served as the starting point of drifting snow. Results indicate that drift-snow transport cannot be defined uniquely unless the drifting snow attains equilibrium (i.e. the snow profile is saturated).

Saltation of snow particles is thought to prevail near the snow surface. However, the vertical flux profile of saltating snow has never been measured. Vertical profiles of drift flux from the snow surface to a height of 30 cm were measured at nine levels, using snow traps composed of nine streamers (compartments). It appears that the saltation flux prevails up to a height of 7-9 cm above the surface, and the suspension flux gradually takes over as the drifting snow develops.
Constant Strain-Rate Tensile Testing of Natural Snow
Authors: Singh H. , Smith F.W.
Published: September 2017

In conducting tension and compression tests on snow samples, strains and strain-rates are usually determined from the displacements of the ends of the samples. In this work, a strain-gage which mounts directly onto the snow sample during testing, was developed and was found to give accurate and direct measurements of strain and strain-rates.

A commercially available 0-28 pF variable capacitor was modified to perform the required strain measurements. It is a polished metallic plunger sliding inside a metal-coated glass tube. The plunger and tube were each soldered to the end of a spring-steel wire arm. To the other end of these arms were soldered to 10 mm square pads made of thin brass shim stock. The whole device weighs 2.5 g and the low coefficient of friction in the capacitor resulted in a very low actuation force. To mount the strain gage, the pads are wetted and frozen onto the snow sample.

A high degree of sensitivity was achieved through the use of “phase-lock-loop” electronic circuitry. The capacitance change caused by the strain in the sample, changes the frequency of output signal from an oscillator and thus causes the change in output from the system. In the locked state, to which the system is constantly driven by a feed-back loop, the system output is almost ripple free.

The strain gages were calibrated in the field in order to take into account the effects of very low field temperatures. The calibration curves were almost linear over the travel of 15 mm, the maximum limit. The sensitivity of the system is 4 mV per strain unit, but this could be increased by an order of magnitude by minor adjustments in the circuit.

Constant strain-rate tensile tests were performed on natural snow at Berthoud Pass, Colorado, U.S.A., in the density range of 140-290 kg m-3. Four strain gages were mounted onto the samples to sense any non-uniform deformation which otherwise would have gone unnoticed or caused scatter in the data. The average indication of these gages was used to construct stress—strain curves for various types of snow at different strain-rates. The effect of strain-rate on the behavior of snow was studied.

“Ratcheting” in the stress-strain curve in the region where the snow becomes plastic was observed first by Kinosita in his compression tests. A similar phenomenon was observed in these tension tests. It was found that directly measured strain is quite different from that which would be calculated from sample end movement. Strain softening was not observed in these tests up to total strains of 8%. The strain-rate effects found were comparable to the results of other investigators.
Monolithologic erosion of hard beds by temperate glaciers
Authors: Lliboutry Louis A.
Published: September 2017

The old problem of erosion by temperate glaciers is reviewed. We restrict ourselves to a monolithologic erosion of hard beds where chemical weathering is almost negligible. Rock fracture, either subglacial or otherwise, may have occurred during a previous cold episode, allowing long-lasting quarrying by the temperate glacier, but, once all the loosened material had been dragged away, grooving becomes the main erosional process. The theory of locally stress-controlled temperatures leads to the idea that very small particles found in the bottom ice cannot reach the bed. Therefore, abrasion and polishing come from rock chips due to grooving or sand grains freed by suglacial chemical weathering. In the steady regime, clasts that are able to groove come from the surrounding rock walls. Most of them do not enter the bergschrund, but are embedded in a bottom layer, which melts progressively over several kilometres. After being in contact with the bed over some distance, they are sufficiently blunted to become unable to groove. This distance. λ, increases with the boulder size, and the largest ones are not yet worn out at the glacier terminus. The mechanics of grooving is roughly modelled to estimate, for any stone size, the grooved volume per unit time and the grooving distance λ. From these estimations, and the size distribution, the erosion rate without quarrying as a function of the distance from the head wall, is calculated. It goes through a maximum when all the debris-laden bottom layer has just melted, and thus an overdeepening might form in a steady way. However, two unknown parameters enter the theory the probability ∏ for a stone able to groove which is in contact with the bed to groove and the ratio k of the volume of grooved rock before the stone is worn out to the volume of the stone. Experiments that may allow us to determine them are indicated below.
Polar ice stratigraphy from laser-light scattering: scattering from meltwater
Authors: Ram Michael , Illing Matthias
Published: September 2017

We describe a new laser-light-scattering instrument for measuring variations in dust concentration along polar ice cores. We have used this instrument with considerable success on the GISP2 ice core from central Greenland. Reproducibility is excellent and the required ice-sample size is relatively small. When combined with visual stratigraphy and ECM, the distinct annual spring/ summer dust peaks we observe can be used to date the core with tree-ring-like precision.
The role of the margins in the dynamics of an active ice stream
Authors: Echelmeyer K. A. , Harrison W. D. , Larsen C. , Mitchell J. E.
Published: September 2017

A transverse profile of velocity was measured across Ice Stream B, West Antarctica, in order to determine the role of the margins in the force balance of an active ice stream. The profile extended from near the ice-stream center line, through a marginal shear zone and on to the slow-moving ice sheet. The velocity profile exhibits a high degree of shear deformation within a marginal zone, where intense, chaotic crevassing occurs. Detailed analysis of the profile, using analytical and numerical models of ice flow, leads to the following conclusions regarding the roles of the bed and the margins in ice-stream dynamics:

(i)

The overall resistive drag on the ice stream is partitioned nearly equally between the margins and the bed and, thus, both are important in the force balance of the ice stream.

(ii)

The ice within the chaotic zone must be about 10 times softer than the ice in the central part of the ice stream.

(iii)

The average basal shear stress is 0.06 × 105 Pa. This implies that the entire bed cannot be blanketed by the weak, deformable till observed by Engelhardt and others (1990) near the center of the ice stream — there must be regions of increased basal drag.

(iv)

High strain rates and shear stresses in the marginal zones indicate that strain heating in the margins may be significant.

While the exact quantitative values leading to these conclusions are somewhat model and location-dependent, the overall conclusions are robust. As such, they are likely to have importance for ice-stream dynamics in general.
Hydrology, erosion and sediment production in a surging glacier: Variegated Glacier, Alaska, 1982–83
Authors: Humphrey Neil F. , Raymond C. F.
Published: September 2017

Outlet streams of Variegated Glacier, Alaska, U.S.A., were observed before, during and after the surge of 1982–83. Measurements of discharge, suspended sediment and dissolved load in the outlet streams are presented for the years 1982–84, and comparisons are made with data from previous years. The data are interpreted to yield characteristics of the basal hydraulic system. The surging region of the glacier was underlain by a basal hydraulic zone of low water velocity and high water storage, inferred to be a distributed-flow system. The ice down-glacier of the propagating surge front was underlain by a high-velocity, low-storage zone, inferred to be a conduit system. The volume of water stored above the surge front was the major hydraulic control on the surge. Basal bedrock erosion during the surge was extreme in comparison to non-surging glaciers. The sediment output was directly proportional to the basal sliding, with a dimensionless erosion rate (meters eroded from the bed divided by meters of sliding) of order 1.0 × 10−4. Total erosion during the 20 year surge cycle was on the order of 0.3 m of bedrock, with approximately two-thirds occurring during the 2 years of the surge peak, and the bulk of this during the peak 2 months.
Thinning of the Ice Sheet in Mizuho Plateau, East Antarctica
Authors: Naruse Renji
Published: September 2017

Surveys of a triangulation chain 250 km in length were carried out in December 1969 and December 1973–January 1974 along the surface contour lines from 2250 m to 2600 m in Mizuho Plateau, East Antarctica. Horizontal velocities were obtained as small values near the Yamato Mountains, while they had maxima of more than 20 ± 0.7 m a –1 around long. 39° E., lat. 72° S. in the drainage of the Shirase Glacier. Submergence velocities showed large values, such as (0.7 to 1)± 0.25 m a–1, in the region along lat. 72° S. from long. 39° E. eastward to long. 43° E. The amount of snow accumulation there, of average thickness 0.2 m a–1, was not enough to compensate for the deficit of the ice mass caused by the submergence flow. It follows that the ice sheet was thinning there. It is suggested that the ice sheet of Mizuho Plateau is in an unstable condition as a whole.
The Basal Sliding of a Thinning Ice Sheet, Mizuho Plateau, East Antarctica
Authors: Mae Shinji
Published: September 2017

The Japanese Antarctic Research Expedition observed the thinning of the ice sheet, about 70 cm/year, in Mizuho Plateau. The thinning observed is analysed using an equation of mass continuity. The result of the analysis indicates that the thinning is predominantly caused by the basal sliding and the basal sliding velocity is about 10 m/year. This sliding velocity is compared with the basal sliding velocity obtained by the calculation of the velocity due to internal deformation of ice sheet.
Measured Velocities of Interior East Antarctica and the State of Mass Balance Within the I.A.G.P. Area
Authors: Young N. W.
Published: September 2017

Recent measurements of accumulation and ice velocity made in the interior of East Antarctica indicate that a large sector between longitudes 80° E. and 135° E. and north of latitude 80° S. has close to a zero net mass budget. This sector is within the study area for the International Antarctic Glaciological Project (I.A.G.P.) and covers a major portion of the area indicated for projects of special emphasis. Velocity measurements were made at a number of points on a traverse route from Mirny (lat. 66° 33′ S., long. 93°00′ E.) on the coast Dome “C” (lat. 74° 40′ S., long. 124° 00′ E.), in the interior. Accumulation measurements were made along this and other traverse routes, extending as far as Vostok (lat. 78° 28′ S., long. 106° 50′ E.), by a number of methods. These included stake, stratigraphic, isotopic, and total β-decay observations. The better accumulation data have allowed a review of the total mass input to be made. The true mass budget has been estimated by comparing velocities, calculated assuming a zero net mass budget with measured velocities along the traverse routes and on a number of the outlet glaciers. For this purpose the area was divided into a number of drainage basins according to outlet at the coast. The area of about 106 km2 and 150 Gt a−1 flux input is drained primarily by three glacier systems of which the Totten accounts for 40% of the flux from 55% of the area; the Vanderford 20% from 15%; and the Scott/Denman 20% from 20%.
Calculations of Velocity and Temperature in a Polar Glacier using the Finite-Element Method
Authors: Hooke Roger LeB. , Raymond Charles F. , Hotchkiss Richard L. , Gustafson Robert J.
Published: September 2017

Numerical methods based on quadrilateral finite elements have been developed for calculating distributions of velocity and temperature in polar ice sheets in which horizontal gradients transverse to the flow direction are negligible. The calculation of the velocity field is based on a variational principle equivalent to the differential equations governing incompressible creeping flow. Glen’s flow law relating effective strain-rate ε̇ and shear stress τ by ε̇ = (τ/B)n is assumed, with the flow law parameter B varying from element to element depending on temperature and structure. As boundary conditions, stress may be specified on part of the boundary, in practice usually the upper free surface, and velocity on the rest. For calculation of the steady-state temperature distribution we use Galerkin’s method to develop an integral condition from the differential equations. The calculation includes all contributions from vertical and horizontal conduction and advection and from internal heat generation. Imposed boundary conditions are the temperature distribution on the upper surface and the heat flux elsewhere

For certain simple geometries, the flow calculation has been tested against the analytical solution of Nye (1957), and the temperature calculation against analytical solutions of Robin (1955) and Budd (1969), with excellent results.

The programs have been used to calculate velocity and temperature distributions in parts of the Barnes Ice Cap where extensive surface and bore-hole surveys provide information on actual values. The predicted velocities are in good agreement with measured velocities if the flow-law parameter B is assumed to decrease down-glacier from the divide to a point about 2 km above the equilibrium line, and then remain constant nearly to the margin. These variations are consistent with observed and inferred changes in fabric from fine ice with random c-axis orientations to coarser ice with single- or multiple-maximum fabrics. In the wedge of fine-grained deformed superimposed ice at the margin, B increases again.

Calculated and measured temperature distributions do not agree well if measured velocities and surface temperatures are used in the model. The measured temperature profiles apparently reflect a recent climatic warming which is not incorporated into the finite-element model. These profiles also appear to be adjusted to a vertical velocity distribution which is more consistent with that required for a steady-state profile than the present vertical velocity distribution.
The Relationship of Ultrasonic Velocities to c-axis Fabrics and Relaxation Characteristics of Ice Cores from Byrd Station, Antarctica
Authors: Gow A. J. , Kohnen H.
Published: September 2017

Deep cores from Byrd Station were used to calibrate an ultrasonic technique of evaluating crystal anisotropy in the Antarctic ice sheet. Velocities measured parallel (Vp ↓) and perpendicular (Vp →) to the vertical axis of the cores yielded data in excellent agreement with the observed c-axis fabric profile and with the in-situ P-wave velocity profile measured parallel to the bore-hole axis by Bentley. Velocity differences ΔV (ΔV = Vp ↓ – Vp→) in excess of 140 m s−1 for cores from below 1300 m attest to the tight clustering of c-axes of crystals about the vertical, especially in the zone 1 300-1800 m. A small but significant decline in Vp ↓ with ageing of the core, as deduced from Bentley’s down-hole data, is attributed to the formation of oriented cracks that occur in the ice cores as they relax from environmental stresses. This investigation of cores from the 2164 m thick ice sheet at Byrd Station establishes the ultrasonic technique as a viable method of monitoring relaxation characteristics of drilled cores and for determining the gross trends of c-axis orientation in ice sheets. The Byrd Station data, in conjunction with Barkov’s investigation of deep cores from Vostok, East Antarctica, also indicate that crystal anisotropy in the Antarctic ice sheet is dominated by a clustering of c-axes about a vertical symmetry axis.
The Dynamics of the Ross Ice Shelf Revealed by Radio Echo-Sounding
Authors: Neal C. S.
Published: September 2017

Radio-echo data have yielded information on the dynamics of the Ross Ice Shelf. Distinctive features present on the radio-echo records have been used to delineate several flow lines on the ice shelf. Measurement of the power returned from the ice-water interface has revealed regional variations in the r.f. dielectric loss of Ross Ice Shelf ice. These variations are used to indicate zones of bottom melting and freezing.
Deduction of Glacier Flow from the Distribution of Elongated Bubbles
Authors: Nakawo Masayoshi
Published: September 2017

The elongation of air bubbles discovered in a wide area of a glacier surface covered by supraglacial debris does not coincide with the direction of flow. When ice samples including elongated bubbles were subjected to simple-shear experiments, the elongated bubbles deformed passively with ice and their final orientation was a good indicator of the strain induced in the ice. Based on these experimental results, the strain and the velocity field of the glacier were deduced from the distribution pattern of the elongated bubbles. The results agreed with the measured flow velocity. The bubble foliation pattern could also be explained in terms of the passive deformation.
First-Order Stresses and Deformations in Glaciers and Ice Sheets
Authors: Hutter Kolumban , Legerer Fritz J.
Published: September 2017

It appears that the well-known theory describing flow of glaciers and ice sheets over undulations is defective with regard to the precise form of the field equations and boundary conditions to be applied. In particular, when surface-wave phenomena are to be described the formulation of Budd does not seem to be applicable.
Dissipation Of Tidal Energy By Flexing Ice Shelves
Authors: Doake C. S. M.
Published: September 2017

Plastic deformation of ice shelves in the region along the grounding line where they bend with the tide can dissipate enough tidal energy to make them the most important single source contribution to tidal friction (Doake, 1978). Some of the effects are to slow the rotation of the Earth and to cause the moon to retreat from the Earth.
Mechanical Properties of Antarctic Deep-Core Ice
Authors: Shoji H. , Higashi A.
Published: September 2017

Tensile tests were carried out with core-ice samples obtained from various depths at Byrd Station, Antarctica in 1968, Specimens for the tests were so prepared as to have their long axes parallel (L specimen), perpendicular (T specimen), and inclined at 450 (I specimen) with respect to the axis of the core, or to the vertical direction of the ice sheet. Stress-strain relations for many specimens were obtained from tensile tests with different strain-rates and also at different temperatures between —10 and — 20°C.
Testing Numerical Models of Glacier Flow
Authors: Waddington E. D.
Published: September 2017

The recent glaciological literature contains a number of numerical simulations of ice-mass flow based on the mass conservation equation. Although rather complex ice masses have been modelled, there has been little discussion of the necessary tests for correct response time and amplitudes in the models. The analytical work of J. F. Nye (1960, 1963[a], 1963[b], 1965[a],1965[b]) on the response of a steady-state glacier to perturbations in its mass balance provides an excellent test of model dynamics. Only when properly verified can the numerical model be used to extend knowledge of glacier response to more general cases where analytical solutions are unavailable. The model in this paper is checked against Nye’s calculations of response to a step increase in mass balance. It is then used to extend Nye’s results by finding the time constants for diffusion parameters other than 0 and 1.
Theory of Deformations within Ice Sheets due to Bottom Undulations
Authors: Johnsen Sigfus J. , Rasmussen Kjeld , Reeh Niels
Published: September 2017

Bedrock undulations of glaciers and ice sheets cause undulations of the ice surface and of internal layers. Models are constructed, that describe this phenomenon, using perturbation techniques and utilizing the stress function as harmonic solution to the full biharmonic equation. This approach is an extension of a previous treatment of the problem, which was based on the solution of the Laplace equation. This solution is shown to be inadequate. Two types of ice flow, with and without bottom sliding, are considered. Furthermore, in order to cope with the variation of viscosity with depth, semi-analytical multi-layer models have been constructed.
Study of Deformations within Ice Sheets due to Bottom Undulations by Means of Radio Echo-Sounding
Authors: Overgaard S. , Rasmussen K.
Published: September 2017

In order to test the theory of glacier flow over bedrock undulations presented by S. J. Johnsen, K. Rasmussen, and N.Reeh in the accompanying abstract, data from the E.G.I.G. and the Dye-3 flow lines on the Greenland ice sheet have been analysed. The data comprise surface profiles measured by conventional techniques, and ice thicknesses and depths of internal isochronic layers obtained by the Technical University of Denmark by means of radio echo-soundings.
Paleoglaciology’s grand unsolved problem
Authors: Grosswald Mikhail G. , Hughes Terence J.
Published: September 2017

The paleoglaciological concept that during the Pleistocene glacial hemi-cycles a super-large, structurally complex ice sheet developed in the Arctic and behaved as a single dynamic system. as the Antarctic ice sheet does today, has not yet been subjected to concerted studies designed to test the predictions of this concept. Yet, it may hold the keys to solutions of major problems of paleoglaciology, to understanding climate and sea-level changes. The Russian Arctic is the least-known region exposed to paleoglaciation by a hypothetical Arctic ice sheet but now it is more open to testing the concept. Implementation of these tests is a challenging task, as the region is extensive and the available data are controversial. Well-planned and coordinated field projects are needed today, as well as broad discussion of the known evidence, existing interpretations and new field results. Here we present the known evidence for paleoglaciation of the Russian Arctic continental shelf and reconstruct possible marine ice sheets that could have produced that evidence.
Velocity and stress fields in grounded glaciers: a simple algorithm for including deviatoric stress gradients
Authors: Blatter Heinz
Published: September 2017

A new and efficient algorithm for computing the three-dimensional stress and velocity fields in grounded glaciers includes the role of deviatoric stress gradients. A consistent approximation of first order in the aspect of ratio of the ice mass gives a set of eight field equations for the five stress and three velocity components and the corresponding boundary conditions. A coordinate transformation mapping the local ice thickness on to unity and approximating the derivatives in the horizontal direction by centered finite-differences yields five ordinary differential and three algebraic equations. This allows use of the method of lines, starting the integration with prescribed stress and velocity components at the base, and a simple iteration procedure converges rapidly.

The algorithm can be used for a wide rangе of stress-strain-rate relations, as long as strain only depends on deviatoric and shear stresses and on temperature. Sensitivity tests using synthetic and realistic ice geometries show the relevance of normal deviatoric stresses in the solutions for the velocity components even for ice sheets. Stress and velocity fields may deviate substantially from the widely used shallow-ice approximation.
The interaction of katabatic winds and the formation of blue-ice areas in East Antarctica
Authors: Van Den Broeke Michiel , Bintanja Richard
Published: September 2017

Blue-ice areas (BIAs) are an extreme example of a local mass-balance gradient and are furthermore reasonably stable in time and space owing to local feed-back mechanisms. A meteorological experiment, performed in and around a blue-ice area in Dronning Maud Land. East Antarctica, showed that during drifting-snow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains, when corrected for surface roughness and stability. This implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing, which is the case for most BIAs. A diagnostic model is tested for a two-dimensional profile in Terre Adélie. after which it is applied to entire East Antarctica. The present order-of-magnitude estimate shows that areas sensitive to blue-ice formation appear where precipitation is low and mean annual wind speed is high, i.e. in Dronning Maud Land and the drainage basin of Lambert Glacier. The results appeared to be especially sensitive to a change in inversion strength: a decrease in inversion strength weakens the katabatic flow, and thus the amount of snowdrift transport, reducing the area where BIAs can develop.
Frequent outburst floods from South Tahoma Glacier, Mount Rainier, U.S.A.: relation to debris flows, meteorological origin and implications for subglacial hydrology
Authors: Walder Joseph S. , Driedger Carolyn L.
Published: September 2017

Destructive debris flows occur frequently at glacierized Mount Rainier volcano, Washington, U.S.A. Twenty-three such flows have occurred in the Tahoma Creek valley since 1967. Hydrologic and geomorphic evidence indicate that all or nearly all of these flows began as outburst floods from South Tahoma Glacier. Flood waters are stored subglacially. The volume of stored water discharged during a typical outburst flood would form a layer several centimeters thick over the bed of the entire glacier, although it is more likely that large linked cavities account for most of the storage. Statistical analysis shows that outburst floods usually occur during periods of atypically hot or rainy weather in summer or early autumn, and that the probability of an outburst increases with temperature (a proxy measure of ablation rate) or rainfall rate. We suggest than outburst floods are triggered by rapid water input to the glacier bed. causing water-pressure transients that destabilize the linked-cavity) system, The correlation between outburst Hoods and meteorological factors casts doubt on an earlier hypothesis that melting around geothermal vents triggers outburst floods from South Tahoma Glacier.
Resolving the Younger Dryas event through borehole thermometry
Authors: Firestone John
Published: September 2017

Meltwater influxes may partly explain the low oxygen-isotope values measured in the Dye 3 and Camp Century ire cores. This has led to speculation that Greenland may not have cooled during the Younger Dryas and underlined the need for independent checks of the oxygen-isotope record.

Using optimal control methods and heat-flow modeling, the author makes a valiant but ultimately futile attempt to distinguish the Younger Dryas event in the ice-sheet temperatures measured at Dye 3, south Greenland. The author discusses the prospects for attempting the same in the new Summit boreholes in central Greenland: how that will require more accurate temperature measurements, a coupled thermo-mechanical model and a refined uncertainty analysis. He concludes by discussing how borehole-temperature analysis may improve the climate histories determined from ire cores.
A method for determining the average height of a large topographic ice sheet from observations of the echo received by a satellite altimeter
Authors: Wingham D.J.
Published: September 2017

Ice-sheet surfaces have scales of fluctuation that arc similar to the diameter of the area illuminated by a satellite radar altimeter. The present theory of altimeter, developed to describe scattering from the ocean surface, does not deal properly with the geometry of ice-sheet surfaces. In this paper, the theory of altimeter is extended to cover this geometry. A general relation for the altimeter echo from a surface of unknown geometry is developed, including the effects of the penetration of the surface by the radar waves. This expression is linearized, using the characteristic operating geometry of satellite altimeters and the gentle nature of ice-sheet gradients. From this expression, an integral equation is derived, from whose solution the spatial average of the height of the surface relative to a spherical datum can be determined. The integral equation is of a Volterra type, which permits the uniqueness of the solution for the average height to be investigated simply. The method is extended to provide a solution for the spatial average of the height of a local region of the ice sheet, provided the region remains large in comparison with the area illuminated by the altimeter, and to deal with variations in the antenna bore-sight alignment. The results have a number of implications for the collection and reduction of echoes in an experiment to determine the average height of an ice sheet. The unique determination of the average height requires the echo to be known over a time interval that depends on the extrema of the surface, which therefore must be known a priori. The average height itself can be determined by the operation on the echo of a linear operator whose kernel is derived from the solution of the Volterra-type equation. This marks a change from the procedures currently used in practice to reduce echoes from ice sheets.
Positive degree-day factors for ablation on the Greenland ice sheet studied by energy-balance modelling
Authors: Braithwaite Roger J.
Published: September 2017

Ice ablation is related to air temperature by the positive degree-day factor. Variations of the positive degree-day factor in West Greenland are studied using an energy-balance model to simulate ablation under different conditions. Degree-day factors for simulated and measured ice ablation at Nordbogletscher and Qamanârssûp sermia agree well with values around 8 mm d−1 °C−1. Degree-day factors for snow are less than half those for ice. Energy-balance modelling shows that degree-day factors vary with summer mean temperature, surface albedo and turbulence but there is only evidence of large positive degree-day factors at lower temperatures and with low albedo (0.3). The greatest effect of albedo variations (0.3–0.7) is at lower temperatures while variations in turbulence have greater effect at higher temperatures. Current models may underestimate runoff from the Greenland ice sheet by several tenths because they use a degree-day factor for melting ice that is too small for the colder parts of the ice sheet, i.e. the upper ablation area and the northerly margin.
Ice Lensing, Thermal Diffusion and Water Migration in Freezing Soil
Authors: Palmer Andrew C.
Published: September 2017

When a surface layer of the soil freezes, both heat and water diffuse from the unfrozen soil beneath to the frozen region. Often the soil does not freeze homogeneously but distinct ice lenses form. An analysis of the diffusion and ice nucleation processes suggests conditions under which ice lensing can be expected; in particular, it is shown that multiple ice lenses cannot form unless the soil thermal diffusivity is greater than the water diffusion coefficient. Analysis of a simple one-dimensional case (a semi-infinite mass of homogeneous soil whose surface temperature is suddenly lowered) gives the temperature and water-content fields as functions of time; these agree with those observed in an experimental study of freezing clay.
The Equation of Continuity and its Application to the Ice Sheet Near “byrd” Station, Antarctica
Authors: Whillans I. M.
Published: September 2017

The continuity relationship that is often used in the study of ice sheets and ice shelves is developed by integrating the equation of continuity through the ice thickness. This equation is then integrated again with respect to horizontal distance from an ice divide, showing that the difference between the true ice velocity and the balance velocity, which is defined, is a measure of the time chance of the mass of a column through the ice thickness.

The relationship is applied using data from along the “Byrd” station strain network, Antarctica. This region is found to be thinning slowly (0.03 m a−1 of ice of mean density) and uniformly, but it is still close to steady-state. The calculations would show a larger thinning rate if bottom sliding contributed more to the ice movement and integral shear contributed less, but the “Byrd” station bore-hole tilting results of Garfield and Ueda (1975, 1976), together with surface velocity measurements at “Byrd” station, indicate that most of the ice flow is by deformation within the ice mass. This large amount of internal deformation is more than that predicted by most “flow laws”, probably because of the strongly oriented ice-crystal fabric in the ice sheet. The cause of ice thinning is probably decreased surface mass balance beginning before A.D. 1550.

The consistent relationship between measured velocity and balance velocity indicates that the ice flow is simple and that flow lines are in the same direction at depth as at the surface when considered smoothed over a distance of 10 km. Because the ice sheet is at present thinning, the balance velocity, calculated only from flow line and surface mass-balance data, and the somewhat mistaken assumption of steady-state is 15% less than the true ice velocity. This rather small difference confirms the use of balance-velocity estimates where velocity measurements are not available.
The Optical Properties of Ice and Snow in the Arctic Basin
Authors: Grenfell Thomas C. , Maykut Gary A.
Published: September 2017

Measurements of light transmission and reflection were carried out on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher’s Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.). Spectral albedos (400-1 000 nm) and extinction coefficients (400-800 nm) were determined for melt ponds, snow, and various types of bare ice. Albedos were largest in the 400-600 nm range, decreasing toward longer wavelengths at a rate which appeared to be related to the liquid-water content of the near-surface layers. Extinction coefficients remained nearly constant between 400 and 550 nm, but increased rapidly above 600 nm. At 500 nm, albedos ranged from 0.25 over mature melt ponds to 0.93 over dense dry snow, while the corresponding extinction coefficients ranged from 0.6 to 16 m-1. Intensity profiles taken in the upper 50 cm of the ice indicated that the extinction coefficient at a particular wavelength was nearly constant with depth below 15 cm, although the bulk extinction coefficient decreased with depth because of the strong attenuation in the red. Near the surface it was found that multi-year ice absorbed slightly more energy than did first-year blue ice, but at depths below 10 cm the flux divergence in the first-year ice was three to four times larger than that in the multi-year ice. A simple procedure is described for estimating light transmission and absorption within the ice under clear or cloudy skies from total flux measurements at the surface. Methods by which satellite data could be used to estimate regional albedos, melt-pond fraction, and lead area are also presented.
Secular Trends of Accumulation Rates at Three Greenland Stations
Authors: Reeh N. , Clausen H.B. , Dansgaard W. , Gundestrup N. , Hammer C.U. , Johnsen S.J.
Published: September 2017

The annual layer thickness profiles along three 400 m ice cores are transferred into accumulation-rate records. A linear decrease of 3±2% per millenium is found in mid-Greenland. Intermediate-term (periods longer than 120 years) deviations from the linear trend lines are less than 5% in mid-Greenland but reach 11% at Dye 3 around A.D. 1700 and 1400. Short-term (periods between 120 and 30 years) oscillations are generally in phase at Milcent and Crête.
Ivory Glacier, New Zealand, an I.H.D. Representative Basin Study
Authors: Anderton P.W. , Chinn T.J.
Published: September 2017

Mass, water, and energy balances were measured lit the Ivory Glacier, South Island, New Zealand from 1969 to 1975 as part of an I.H.D. programme of representative basin studies. Ivory Glacier is a small cirque glacier within the high-precipitation maritime environment of Westland and was chosen initially for convenience of study rather than representativeness. Mass-balance investigations included a detailed study of the sampling efficiency of a pole network. Annual mass balance was consistently negative during the study period. The run-off pattern was dominated by rain. The estimated annual mean precipitation is 9630 mm for 1971-75. Snow represents about 25% of annual precipitation. Melt contributed 21% of run-off including 9% contributed by melt of perennial snow and ice. The relative contributions of different fluxes to the energy balance during summer are: net radiation 52%, sensible heat 29%, and latent heat 17%. Heat content of precipitation contributes significantly to the energy balance during individual rain-storms and is probably significant during periods of high precipitation in spring and autumn. Climatic characteristics and behaviour of Ivory Glacier appear to follow regional trends in the Southern Alps and the glacier is considered to be reasonably representative.
Sediment Concentration in Melt Waters as an Indicator of Erosion Processes Beneath an Alpine Glacier
Authors: Collins David N.
Published: September 2017

Suspended-sediment concentrations in melt waters from the Gornera, Gornergletscher, Switzerland, were determined at hourly intervals for periods during the ablation seasons of 1974 and 1975. Rapid erratic fluctuations of suspended-sediment concentration produced peaks which occurred both before and after highest daily flows. Clockwise daily hysteresis rating loops between sediment concentration and discharge included many involutions. Suspended-sediment-concentration-discharge rating curves were different for rising and falling limbs of individual diurnal hydrographs and varied from day to day. Close-interval measurements of sediment concentration and discharge records allow interpretation of the nature of ice–water–sediment interactions at the bed of an Alpine glacier. At Gornergletscher, subglacial sediment is delivered to melt waters flowing in the smaller basal conduits, which often change course suddenly, entraining unworked sediment stored at the bed. During diurnal discharge maxima, sediment concentration in the Gornera is reduced because the rate of increase of water volume outstrips the rate of supply of sediment. The drainage of the ice-dammed lake Gornersee, producing exceptionally high flows, extended the drainage network over large areas of the glacier bed, and evacuated much sediment.
Plough Marks in the Weddell Sea
Authors: Orheim Olav
Published: September 2017

The 1976/77 Norwegian Antarctic Research Expedition carried out studies of the sea bed by side-scan sonar. The equipment was operated from the expedition vessel down to about 350 m depth by personnel from the Continental Shelf Institute, Trondheim. Various types of plough marks mostly ranging from 10 to 100 m in width were observed. These included several generations of crossing plough marks as well as plough marks with abrupt changes in trend reflecting changing iceberg motion. The investigations will be expanded during the 1978/79 expedition to include towing at greater depths, and mapping of sea-bed morphology by mosaic towing patterns.
Water Movement At The Base Of Ice Sheets
Authors: Whillans I. M.
Published: September 2017

Flat-surfaced subglacial lakes, such as those discovered by Oswald (1975), can form where basal sliding velocities are low. As the glacier moves onto a subglacial lake, its underside retains the shape of the vertical relief at the lake edge. Differential heat transfer from the lake into high and low points in the interface flattens the surface by extra melting of the downward projections or freezing in the high areas. A time of the order of 103 years is required to flatten the fluting, and the down-glacier part of a subglacial lake can be flat-surfaced if the glacier takes longer than some 103 years to traverse the lake. Such a slow traverse time is expected near ice-drainage divides, and it is there that flat-surfaced lakes were discovered by radar sounding.
Ice At Melting Point Sliding Over A Pebble Slab–A Film
Authors: Budd W. F. , Blundy N. A.
Published: September 2017

A time-lapse movie technique has been developed to study processes taking place near the interface when ice under high normal stress slides over a rough slab for shear stresses and sliding velocities comparable to those of real glaciers.

The “sledge rig” described by Budd and others (1979) was set up with one of the strips of ice (160 mm long and 23 mm wide) close to the edge of the pebble slab on which it rested. The normal stress was applied by loading the rig with lead to 5 bars. The shear stress was applied by a direct load on a cable over a pulley while the rig rested on the slab on a strong table. Shear stresses in the range 1 to 2 bars were used giving velocities from about 50 to 500 m a–1. Beyond 2 bars it was found that acceleration would set in, so this was avoided.

A time-lapse movie camera was set up beside the rig to focus first on the whole configuration and then on the ice and interface as a close-up. A flash light was set up behind the rig to shine through the ice strip. A scale rule was placed along the slab under the ice strip. A dial-gauge micrometer was also used to monitor displacement.

A time-lapse frequency of about 1 frame per 8 s was found to give a suitable speed. An automatic control triggered the camera and flash and also recorded the number of frames. A number of different markings were tried on the ice to indicate the relative ice deformation. Small graphite particle tracers were found the most successful.

A number of runs have been filmed showing the ice sliding speed increasing with increasing shear stress. The tests were carried out in a cold room at a temperature close to 0°C.

Copies of the film can be made available at cost.

The authors were greatly assisted by Mr David Gardner of the Department of Educational Technology of Melbourne University by the provision of the filming equipment and general support for the operation.
Abstracts of Papers Presented at the Symposium But Not Published in Full in this Volume: Subglacial, Englacial, and Supraglacial Sediment Differentiation and Erosion in Glacial Basins
Authors: Rogerson R. J. , Eyles N.
Published: September 2017

If sediments being transported by glaciers in subglacial, englacial, and supraglacial situations can be differentiated on the basis of their textural characteristics, some potential exists for interpreting the relative importance of subglacial and sub-aerial periglacial processes in the excavation of glacial valleys, by examining the sediments in abandoned or active terminal moraines. Caution should be used with compound glacial valleys where subglacially eroded debris may become englacial as ice streams merge, be subsequently transported passively, and in terminal moraine deposits appear to represent sub-aerially derived sediments.
Erosion of Grooves by Subglacial Melt-Water Streams
Authors: Whillans I. M.
Published: September 2017

The shape of the former Laurentide ice sheet in what is now northern Ohio and southern Ontario is calculated and the subglacial hydrological potential field computed. Subglacial water flow is found to be concentrated over high points in the bed, such as what is now Kelleys Island in Lake Erie. Some 1010 litres of subglacial melt water per year passed over Kelleys Island.

It is argued that the “glacial” grooves on Kelleys Island are subglacial melt-water channels. Assuming that the subglacial melt water attained saturation with respect to CaCO3, in passing over the limestone of Kelleys Island, the material formerly occupying the grooves could have been dissolved in 102 years. This is a much shorter time than glacier occupancy and the assumption of chemical equilibrium is not critical.

The features on Kelleys Island are fluted valleys about 6 m across and each flute is about 0.1 m in width. Each flute represents a subglacial channel but only one or two of these channels operated at any one time. Blockages, perhaps caused by basal debris, caused the rivers to make minor course changes and in many instances it is possible to determine the order of channel occupancy. The channels were striated after abandonment by water when moving basal debris or debris-laden ice occupied the channels. From the Gauckler-Manning formula and the potential gradient obtained from the ice-sheet model the river velocity is calculated to be about 4 m s–1, in rough agreement with the water flux calculated earlier.

The grooves support the concept that subglacial water flows in “Nye” channels, and raise the suggestion that subglacial erosion by solution is of widespread importance.