bluuebunny/crossref_metadata_2025 huggingface dataset:
Deuterium, Tritium, andβactivity in a snow core taken on the summit of mont blanc (french alps). Determination of the accumulation rate
Authors: Jouzel J. , Merlivat L. , Pourchet M.
Published: September 2017

Deuterium, tritium, and grossβactivity measurements have been performed to a depth of 16 m on a snow core taken on Mont Blanc (French Alps) to establish a chronology of its formation and then deduce the annual accumulation. These three independent methods show that the core was formed over a three-year period. This corresponds to a mean annual accumulation of 2.8 m water equivalent In addition, the isotopic measurements indicate the existence of an altitude effect in the distribution of deuterium and tritium in the precipitation in the Mont Blanc area.
Local Friction Laws for Glaciers: A Critical Review and New Openings
Authors: Lliboutry L.
Published: September 2017

“Sliding velocity” and “friction law” are precisely defined. Different scales for tackling glacier dynamics are introduced. The energy balance in the melting-refreezing process is clarified. The validity of a Glen body as a model for ice rheology is discussed. The assumed model for subglacial water is a very slightly pervious ice, and a not absolutely watertight ice-bedrock interface, owing to glacial striae and rock joints. Then autonomous hydraulic regimes and cavities at water vapour pressure have a negligible influence on the drag, and only the interconnected regime has to be considered.

A more rigorous treatment of Weertman’s model (independent knobs) gives quite different numerical factors. In general a term increasing with Terzaghi’s effective pressure N has to be added to the drag. The double-valued friction law found by Weertman is shown to have been an error.

Kamb’s relations for the model with a vanishing microrelief are considerably simplified. His conjectural solution cannot be extended to slopes actually found in the microrelief.

The author’s (Lliboutry, 1968) treatment is unsatisfactory and includes an error. With a model consisting of irregular bumps of similar length, a new friction law is given. The pertinent measure of the bedrock roughness is then the shadowing function, not the spectral power density.
The Unsolved General Glacier Sliding Problem
Authors: Weertman J.
Published: September 2017

The status of the theory of glacier sliding is reviewed in this paper. The theory of Nye and Kamb essentially solves the problem of glacier sliding when the basal ice is in intimate contact with a non-deformable bed. But experimental work is needed on cyclic creep and the regelation process in order to put better numbers into the theory. The outstanding problem that remains to be solved, called in this paper the general glacier sliding problem, is the case of sliding when basal ice is not in intimate contact with a non-deformable bed because of the presence of cavities and a water film of finite thickness. This problem involves solving an intricately coupled basal water-flow problem. A new field of research is the study of the motion of glaciers over deformable beds.
Empirical Studies of Ice Sliding
Authors: Budd W. F. , Keage P. L. , Blundy N. A.
Published: September 2017

An experimental programme has been carried out for studying temperate-ice sliding over rock surfaces with a wide range of roughnesses, for normal and shear stresses comparable to those expected under real ice masses. The limiting static shear stress for acceleration has been found to be directly proportional to the normal load giving a constant limiting coefficient of static friction characteristic of the surface. For a constant applied normal stress N and shear stress τb, well below the limiting static shear, a steady velocity Vb results which increases approximately proportionally to τb and decreases with increasing N and the roughness of the surface. For high normal stress the velocity becomes approximately proportional to the shear stress cubed and inversely proportional to the normal stress. As the shear stress increases acceleration sets in, which, for different roughness and normal loads, tends to occur for a constant value of the product τbVb. For some surfaces at high normal loads this acceleration was retarded by erosion. For constant-applied-velocity tests a steady shear stress resulted, which tended to become constant with high velocities, and which increased with increasing normal stress but with a reduced coefficient of sliding friction. The relevance of the results to the sliding of real ice masses is discussed with particular reference to the importance of the effect of the relative normal stress, above basal water pressure, to the sliding rate.
Seismic Evidence for Discrete Glacier Motion at the Rock–Ice Interface
Authors: Weaver Craig S. , Malone Stephen D.
Published: September 2017

Seismic monitoring on three Cascade volcanoes in Washington State, U.S.A., has shown that small seismic events are generated by the active glaciers found on each mountain. Detailed seismic experiments have been conducted to investigate the sources for these icequakes. Considerable evidence indicates that the events are the result of a stick–slip type of motion taking place at the bed of the glaciers. The few events we have been able to locate had depths comparable with the glaciers’ thickness. The similarity of wave form from an explosion at the bottom of a glacier and natural icequakes suggests that the complexity of the seismic wave form is due to the path and not the source. The events exhibit an annual trend with more events being recorded in the summer than during the winter. A ten-fold increase in the number of events preceded a large ice avalanche that involved the entire glacier thickness, suggesting that seismic monitoring may be useful in predicting catastrophic ice movements.
Giant Grooves Made by Concentrated Basal Ice Streams
Authors: Goldthwait R. P.
Published: September 2017

Glacial grooves are known on all the flat-lying limestone islands in western Lake Erie. The largest megagroove complexes are on Kelleys Island, each 2–6 m deep, 5–20 m wide, and 100–400 m long before quarrying. Each megagroove floor is rolling with second-order rounded ridges and “sine-shaped” grooves 10–90 cm deep, and 5–40 m long. Furthermore, these are gouged laterally by sharply curving and nesting gouges up to 10 cm deep. All grooves exhibit third-order striation up to 1–2 mm deep and 5–200 cm long made by individual tools of debris traveling mostly 240–260°.

Ice of the Erie lobe was under compressive flow as it rose from 9 m below present lake level to 12 m above. Some sort of ice vortices (fixed eddies in the basal ice stream) are postulated to make the scoop marks and ridge ends. Fast-moving ice rather than water or a slurry is favored because there are no percussion marks. Very likely, a till mat of interfering engraving points is required. A strong convergence (2× to 10×) of striae into the deepest grooves indicates squeezing together of the debris tools and increase in local ice velocity. Interglacial subareal streams may well have shaped the initial trough up which these ice streams concentrated, because dendritic tributary grooves intersect, and main groove sets curve as much as 10° or 20°. Furthermore, sharp 100–180° meander curves are preserved at the bottom of the deepest grooves. Hiram-age clay-till with rare erratics half fills the original grooves; it shows that this groove cutting was completed before 15 500 14C years ago.
Direct Measurement of Basal Water Pressures: Progress and Problemss
Authors: Hodge Steven M.
Published: September 2017

In 1975 and 1977, 24 bore holes were drilled to the bed of South Cascade Glacier, Washington, U.S.A., using both electrothermal and hot-water drills. Only two holes connected directly with the basal water system, a significant decrease from the four to five such connections in 13 holes drilled in 1973 and 1974 (Hodge, 1976). Most of the bed, possibly as much as 90%, appears to be hydraulically inactive and isolated from a few active subglacial conduits. Bore holes which penetrate these inactive areas initially should connect eventually with the active basal water system due to bed pressurization by the water standing in the bore hole, provided there is a sufficient supply of water available to form and maintain the connection passageway. These sealed-off areas probably consist of the sub-sole drift and permeability barriers found recently at the bed of Blue Glacier by Engelhardt and others (1978); an increase in the area of bed covered by these features probably caused the decrease in chance of bore-hole connection. This apparently was not due to any external cause but rather was the result of a real internal change in the subglacial hydraulic system which occurred between 1974 and 1975.

If most of the area of a glacier bed is hydraulically isolated sub-sole drift, or something similar, such features may well control large-scale glacier sliding changes, since changes in the amount of water having access to the glacier bed will take considerable time to affect the interstitial water pressure in the more widespread sub-sole drift.

Water pressures in the active part of the basal water system of South Cascade Glacier are generally in the range of 50–75% of the ice overburden pressure. Water levels in a connected bore hole are probably representative over an area of the bed 100 m or more in extent. A correlation of bore-hole water levels with changes in surface motion supports the idea that the sliding of a temperate glacier is controlled largely by the basal water pressure.
Quantitative Determination of the Subglacial Hydrology of Two Alpine Glaciers
Authors: Collins David N.
Published: September 2017

Two components of discharge through the internal hydrological systems of Alpine glaciers were separated on the basis of chemical composition of water. Some surface melt waters retain low solute contents after flowing without delay through conduits in which no chemical enrichment occurs, whereas those flowing slowly at the glacier bed have increased ionic concentrations. A simple mixing model was used to investigate temporal variations in the quantities of water routed through each of the two sub-systems. Electrical conductivity was taken as an indicator of melt-water composition and was monitored for periods during the summer ablation season of 1975 at Gornergletscher and of 1977 at Findelengletscher. At both glaciers, conductivity of melt waters varied diurnally inversely with discharge fluctuations, depending on the proportion of total discharge routed through the two sub-systems. Total discharge and the flow component routed rapidly through conduits within the glacier, a large proportion (50–80%) of total discharge, exhibited in-phase rhythmic diurnal hydrographs at the two glaciers. Distinctive subglacial hydrological regimes are contrasted. At Findelengletscher, the hydrographs of total discharge and of subglacial chemically enriched flow were in phase. At Gornergletscher, the subglacial hydrograph occurred with reverse asymmetry and out of phase. A possible interpretation is that water was temporarily stored in basal cavities during high total discharge. During the night, stored water was released, contributing much of the total discharge at times of low flow.
Characterizing the Glacier Bed Using a Radio-Echo Technique
Authors: Doake C. S. M.
Published: September 2017

If glacier ice is assumed to be a uniaxial birefringent material then two parameters are needed for describing the orientation behaviour of the polarization ellipse of a radio signal returned from the glacier bed. These are δ, the relative phase between the ordinary and extraordinary wave, and r, the ratio of their attenuation coefficients (Woodruff and Doake, 1979). If it is assumed that the attenuation in ice is isotropic, then a value of r other than unity will be due to anisotropic reflection coefficients at the glacier bed. A simple way of measuring r separately from δ could then be used to characterize the reflecting surface.
Basal Sliding and Bed Separation: Is There a Connection?
Authors: Bindschadler Robert
Published: September 2017

Analysis of field data from Variegated Glacier supports the conclusion of Meier (1968) that no simple relationship between basal shear stress and sliding velocity can be found. On the other hand, an index of bed separation is defined and evaluated that correlates very well with the longitudinal variation of summer sliding velocity inferred for Variegated Glacier. This bed separation parameter is defined as

where τ is the basal shear stress and is proportional to the drop in normal stress on the down-glacier side of bedrock bumps and Neff is the effective normal stress equal to the overburden stress minus the subglacial water pressure. The water-pressure distribution is calculated assuming water flow to be confined in subglacial Röthlisberger conduits. The excellent agreement between the longitudinal profiles of I and sliding velocity suggests that calculations of the variation of bed separation can be used to deduce the variation of sliding velocity in both space and time. Further, it is possible that a functional relationship can be developed that adequately represents the geometric controls on basal sliding to permit accurate predictions of sliding velocities.
The Nature of the Ice-Rock Interface: The Results of Investigation on 20 000 m2 of the Rock Bed of Temperate Glaciers
Authors: Vivian Robert
Published: September 2017

This paper reviews the results of ten years study of the only four subglacial sites which are permanently accessible thanks to the work of hydro-electrical companies. All the sites occur beneath temperate ice. The first part is devoted to the study of the rock-ice interface as a glaciological phenomenon. The dynamic conditions for separation of the ice from the rock bed are considered. This cavitation phenomenon occurs when tan α > Vi/Hi. “Regressive cavitation” explains the existence up-stream of large permanent cavities and of a series of small cavities which, although they are not permanent, are fundamental because they control sub-glacial water drainage. The second part analyses the sliding movement of ice on a rock bed. Indeed the deformation of the cavities depends mainly on the variations in the velocity of the glacier. The sliding velocity measured at the interface accounts for 60 to 80% of the surface movement of the glacier. 80 to 90% of the surface velocity is attained a few metres above the glacier-bed interface. The third part describes the characteristics of subglacial drainage which are necessary to understand the nature of the ice-rock interface. The fourth part is devoted to the precise description of the different types of interface as they appeared in the subglacial sites.

This paper has been accepted for publication in full in a future issue of the Journal of Glaciology.
Marks and Forms on Glacier Beds: Formation and Classification
Authors: Laverdière Camille , Guimont Pierre , Pharand Michelle
Published: September 2017

Glacial erosion wears the bedrock grain by grain, that is it breaks free a multitude of little fragments. It also acts upon the bedrock to cause trains of concentric fractures and quarried surfaces. Since this type of erosion is selective in places of variable resistance, it brings about dug-out forms like grooved joints, or salient forms like veins carved out from up-stream down, it produces small-scale features like grooves or chattermark trains or, on a larger scale, acts upon rocky knobs to produce roches moutonnées; the latter, in spite of their dimensions, are subject to an action that can still affect every point simultaneously. Our objective is thus to present hierarchically the glacial forms left on the bedrock, along with the terminology that designates them. In Table I we give both English and French terminology, but it is not our purpose to make definite proposals for the few new terms in English.
The Ice-Rock Interface and Basal Sliding Process as Revealed by Direct Observation in Bore Holes and Tunnels
Authors: Kamb B. , Engelhardt H. F. , Harrison W. D.
Published: September 2017

The glacier bed, where basal sliding occurs, was reached by cable-tool drilling and sand-pump bailing in seven bore holes in Blue Glacier, Olympic National Park, Washington. Basal sliding velocities measured by bore-hole photography and confirmed by inclinometry are unexpectedly low, ranging from 0.3 to 3.0 cm/day and averaging 1.0 cm/day. This is much less than about half the surface velocity of 15 cm/day, which was the sliding-rate expected from earlier deformation measurements in bore holes made by thermal drilling alone.
Glacier-Bed Landforms of the Prairie Region of North America
Authors: Moran S. R. , Clayton Lee , Hooke R. LeB. , Fenton M. M. , Andriashek L. D.
Published: September 2017

Two major types of terrain that formed at or near the bed of Pleistocene continental ice sheets are widespread throughout the prairie region of Canada and the United States. These are (1) glacial-thrust blocks and source depressions and (2) streamlined terrain.

Glacial-thrust terrain formed where the glacier was frozen to the substrate and where elevated pore-water pressure decreased the shear strength of the substrate to a value less than that applied by the glacier. The marginal zone of ice sheets consisted of a frozen-bed zone, no more than 2 to 3 km wide in places, within which glacial-thrust blocks are large and angular. Up-glacier from this zone the thrust blocks are generally smaller and smoothed. Streamlined terrain begins 2 to 3 km behind known ice-margin positions and extends tens of kilometres up-glacier. Streamlined terrain formed in two ways: (1) erosion of the substrate as a consequence of basal sliding in the sub-marginal thawed-bed zone and (2) erosional smoothing accompanied by emplacement of till in the lee of thrust blocks where they were deposited and subsequently exposed to thawed-bed conditions as a result of further advance of the glacier.

This paper has been accepted for publication in full in a future issue of the Journal of Glaciology.
Piezometric Observations of Water Pressure at the Bed of Swiss Glaciers
Authors: Röthlisberger H. , Iken A. , Spring U.
Published: September 2017

A technique for drilling deep holes with a hot-water jet has been developed in recent years at our institute (Iken and others, [1977]). The holes have served to investigate the water pressure at the bed of various Swiss glaciers since 1973. Drainage occurred naturally in rare cases when the drill reached the bed, but more often it was necessary to use explosives first, probably because the drill was stopped short of the bottom of the glacier by rock inclusions in the ice. In order to record piezometric water pressure over an extended period of time it was necessary that water was draining fairly continuously into the hole, otherwise the water level dropped eventually to a great depth when the weather turned cold, whereupon the holes closed off. By suddenly shutting off the water supply to a hole and observing the lowering of the water level with time some information on the channel characteristics has been obtained. In many cases there was little change of level, indicating that such a hole gives almost the true pressure head of the subglacial drainage system.

Our efforts have so far been concentrated on flat tongues of fair size over 100 m thick, the distance from the uppermost hole to the terminus ranging from about 1 to 4.5 km. The main characteristic of the water pressure is a very large diurnal variation of the order of 100 m and more. The mean pressure generally rises and falls in times of high and low water supply, respectively, but re-adjusts to approximately the original level within a few days. Mean levels are higher early in the melt season than later, and the amplitude of the diurnal variation has a tendency to increase with time, but also shows strong short-term modulations depending on the water supply. From observations on moulins and a hole which had remained connected to the bed from the previous year it seems likely that at the beginning of the melt season the water pressure at the bed may become as large as or larger than the ice pressure.

On Gornergletscher a record of water pressures has been obtained during the drainage of Gornersee, an ice-dammed lake at the confluence of the two main branches of the glacier. Levels stayed high day and night in the piezometer holes, which were located off to the side of where the main drainage channel was suspected to pass through. The surface drainage pattern was affected over a large area of the glacier. These two observations indicate that during the drainage of the lake some sort of sheet flow must have occurred. The surface velocity of the glacier roughly doubled during that time, but no lifting-up of the ice was observed within the accuracy of the survey. On one occasion on Glacier de Breney the main channel must have been blocked temporarily between an upper area, where the water level was rising simultaneously in three piezometer holes, and an area further down-glacier, where the holes were not affected.
Interdependence Between Glacier Erosion and Geological Features
Authors: Arenillas M. , Mantinez de Pison E. , Samartin A.
Published: September 2017

A strong relationship between the shapes of glacier excavation and some specific structures of the bedrock seems to exist in all the cases observed by the authors. Important examples of this kind include present and Quaternary glaciers in the Iberian Peninsula, the Alps, and the Peruvian Andes. A preliminary mathematical model has been developed, a brief description of which is given in this paper. Within the framework of this model the above interdependence can be interpreted. In this way the excavation mechanism that occurs in stationary glaciers can be explained without requiring the use of more sophisticated theories implying quite complex morphological phenomena. Suggestions for further studies are also made.
Glacial-Bed Types and Their Radar-Reflection Characteristics
Authors: Reynolds R. , Whillans I. M.
Published: September 2017

Studies of radar reflection characteristics can indicate much about the bed of an ice sheet and the associated ice motion. This contribution analyzes the relative significance to the ice flow of rough ice-rock, rough ice-water-rock, and flat ice-water-rock interfaces, and establishes criteria for distinguishing among these interface types under ice sheets using radar equipment of the type developed by the Technical University of Denmark.
Reconciliation of Temperature-Depth Profiles in Polar Ice Sheets with Past Surface Temperatures Deduced from Oxygen-Isotope Profiles
Authors: Robin G. de  Q.
Published: September 2017

Investigations of isotopic and temperature profiles in polar ice sheets were mostly carried out independently of one another until 1973 when a workshop dealing with both topics was held in Cambridge. Studies of temperature profiles show the approximate validity of theoretically derived temperature distributions for steady-state models of ice sheets, while other analyses help to determine departures from the steady state. The review gives some idea of the degree of accuracy of various solutions arising from studies of the heat flow and temperature distribution of ice sheets. Much of this knowledge is directly applicable to interpretation of isotopic profiles if a direct correspondence between mean isotopic δ values and mean annual temperatures can be established. The paper therefore reviews various methods of comparing δ values and temperatures, and shows that for central regions of polar ice sheets a reasonably consistent relationship between these factors does exist.
Microwave Emission From Snow and Glacier Ice
Authors: Chang T.C. , Gloersen P. , Schmugge T. , Wilheit T.T. , Zwally H.J.
Published: September 2017

The microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.
The Theory of Thermal Convection in Polar Ice Sheets
Authors: Hughes T.J.
Published: September 2017

Application of thermal convection theory to polar ice sheets (Hughes, 1970, 1971. 1972[a],[c]) is reviewed and expanded. If it occurs, thermal convection is mainly concentrated near the bed of the ice sheet; resulting in active and passive convective flow, respectively below and above the ice density inversion. Convection begins as transient creep when a stress-independent critical Rayleigh number is exceeded, and stabilizes as steady-state creep when a stress-dependent critical Rayleigh number is exceeded. Transient- creep convection begins as unstable ripples in isotherms near the bed, with some ripples becoming upward bulges of basal ice which rapidly shrink laterally and grow vertically to become ascending dikes of recrystallized basal ice during steady-state creep. Sills of basal ice are injected horizontally between weakly coupled layers in the strata of cold ice slowly sinking en masse between dikes. Convection begins under domes of thick ice toward the ice-sheet center and a stable polygonal array of dikes may form if frictional heat creates hot ice at the bed as rapidly as convection flow redistributes hot basal ice in dikes and sills, Advective flow transports the converting ice toward the margin of the ice sheet where dikes converge at the heads of ice streams. Dike—sill convection then becomes ice-stream convection in which the entire ice stream behaves like a dike, uncoupling from the bed, and rising en masse. This would help explain why ice streams flow at surge velocities.
Field Observations and Experimental and Theoretical Studies on the Superimposed Ice of McCall Glacier, Alaska
Authors: Wakahama Gorow , Kuroiwa Daisuke , Hasemi Tatsuo , Benson Carl S.
Published: September 2017

The formation of superimposed ice in the accumulation area of sub-polar glaciers plays an important role in the heat and mass balance of the glaciers. In order to study the process of superimposed ice formation in detail, field observations were conducted on McCall Glacier, a sub-polar glacier in Arctic Alaska. It was found that the approximate thickness of superimposed ice formed in a whole summer was 20 cm in the upper region and 30—40 cm in the lower region of the accumulation area of the glacier. This difference in thickness may be attributed to the difference in the temperature of the underlying ice and the rate of supply of melt water. The ratio of the amount of superimposed ice formed in the accumulation area from May to July in 1972 to the total amount of melt was determined. Approximately 50% of the total melt water was discharged from the glacier as run-off water, and the remainder contributed to the formation of superimposed ice.

An experimental study on the artificial formation of superimposed ice was conducted in the cold laboratory to obtain the ratio of superimposed ice, that of run-off water, and that of free water suspended between snow grains, to the total amount of melt water produced in the snow. The ratios obtained in the laboratory experiment agree fairly well with those derived from the observational data on McCall Glacier.

Numerical calculations were conducted to examine the relationship between the growth rate of superimposed ice, the rale of snow melting, the rate of discharge of excess melt-water, and the temperature of the underlying ice. Calculations were made in reference to both the laboratory experiment and the field observations on McCall Glacier. It was found that the predominant factors controlling the growth rate or the total amount of superimposed ice in a sub-polar glacier are the rate of supply of melt water to the snow-ice interface and the initial temperature distribution in the underlying ice. By using the present calculation, it may be possible to estimate the growth rate, the total amount of superimposed ice, and the ratio of superimposed ice to the total amount of melting in the accumulation area of any sub-polar glacier, if observational data on the initial temperature distribution in ice and the rate of snow melting at the snow surface are available.
Physical Processes in Temperate Glaciers
Authors: Lliboutry L.
Published: September 2017

In a temperate glacier ice the water content results from the past history of the ice, and the temperature adjusts itself to the appropriate value. Results obtained by the Laboratoire de Glaciologie are summarized. Several facts seem to prove some migration of the liquid phase and a coalescence of liquid inclusions. The enthalpy flux is calculated, but it cannot be proved that a spontaneous gathering together of liquid inclusions could occur. The water-rich, small grain-size layers should come from the lowering of the viscosity when the water content increases, as discovered by Duval. The form of Weertman’s sliding law without cavitation can be derived from simple dimensional considerations. Numerically, it cannot account for high sliding velocities, for which subglacial cavitation must be introduced. The cavities are infilled with more stagnant regelation ice than water. Two subglacial hydraulic regimes are distinguished: autonomous and interconnected. The effect which the salt content may have on cavitation is estimated.
Direct Measurement of Basal Water Pressures: a Pilot Study
Authors: Hodge Steven M.
Published: September 2017

Bore-hole drilling techniques have been used to connect with the subglacial water system of the temperate South Cascade Glacier. The water level in a connecting bore hole probably represents a direct measurement of the basal water pressure over an area at least to m in extent. Fluctuations of up to 40 m in bore-hole water levels occur typically over periods of several days and often peak about 2 d after large changes in water input at the glacier surface. The long-term trend in bore-hole water levels supports the idea of seasonal storage and release of liquid water.
Geo-Hydrologic and Thermometric Observations in the Vicinity of the Columbia Icefield, Alberta and British Columbia, Canada
Authors: Ford D.C. , Harmon R.S. , Schwarcz H.P. , Wigley T.M.L. , Thompson P.
Published: September 2017

The Columbia Icefield rests upon limestones containing natural caves that drain waters from the glacier sole. The principal cave is sealed at one end by an extrusion of glacier ice 300 m below the icefield surface. The hydrologic regime of the cave indicates that the modern icefield is temperate in character and that water is present at the glacier sole throughout the year. An interpretation of the air temperature pattern in the cave suggests that the geothermal flux to the glacier is only 10-40% of the expected value because heat is abstracted by melt water circulating through the rock. U, Th and O isotopic analyses of calcite speleothems further indicate that the base of the icefield has probably been temperate throughout the past 150000 years. The cave was inundated when glaciers expanded during the classical Wisconsinan main Würm period. The inundation implies maintenance of a permanent water table at some hundreds of meters above the base in a valley glacier 750—800 m in depth.
Thermal Regime of a Surge-Type Glacier
Authors: Bindschadler Robert , Harrison William D. , Raymond Charles F. , Gantet Claude
Published: September 2017

Recent measurements of near-surface temperature and surface velocity from the Variegated Glacier are presented. Temperature was measured with thermocouples at nine sites spaced along the length of the glacier. Maximum measurement depths ranged from 8 m in the lower ablation area to 20 m in the accumulation area. Accuracy of measurement was about 0.1 deg. By the end of summer the temperature at all measured sites and depths was not measurably different from zero, indicating that practically all of the near-surface ice of the glacier is temperate. The distribution of surface velocity along the length of the glacier shows distinct variations with time which cannot be explained by internal deformation in the glacier as influenced by changes in ice depth and slope. This indicates that the glacier is sliding over much of its length, which requires that the base of the glacier is temperate. Taken together, the near-surface temperature and velocity data provide good evidence that Variegated Glacier is temperate throughout and also indicate that the surge behavior of this glacier cannot be explained by thermal triggering.
Bridge Optimization for Thermistor Measurements
Authors: Narod B. Barry
Published: September 2017

An expression for optimum bridge parameters is derived for a thermistor in a Wheatstone bridge and numerical values are assigned to determine the useful limits of resistance bridges tor thermistor measurements. Several digital ohmmeters are evaluated as measuring devices and are shown to compare unfavourably with a simple bridge and null detector.
Future Regard to the Atomic Waste Disposal Problem
Authors: Philberth K.
Published: September 2017

The waste disposal in an ice sheet need not rely on storage periods longer than some hundreds of years. Three hundred years after dumping, the radioactive power of the fission products has decreased to about 10-4 times the value of two-year-old waste. Six hundred years after dumping, it has decreased to about 10-6 times the two-year value. There are only four radioactive fission.isotopes with half-lives between six years and 60000 years: 85Kr (10 years) has practically disintegrated after 300 years. 90Sr (with its daughter 90Y) and 137Cs (both 30 years) are reduced to 10-3 after 300 years and to 10-6 after 600 years. 151Sm (85 years) has an extremely low disintegration energy; the waste contains only a very small percentage of this isotope.

Radiation and thermal power of all fission products with long half-lives (more than 60 000 years) are many orders of magnitude smaller than those of all other fission products in waste that has been stored for several years. Furthermore, long-lived fission products have almost no radiation other than β-radiation. Future research is necessary as to whether and to what extent such long-lived isotopes, and possibly other isotopes (c.g. 239Pu or 14C), have to be separated and as to how it could be done in the safest and most economical way. The technology of separating and recycling 239Pu, an extremely valuable fissionable fuel, is being developed in view of the increasing importance of breeder reactors. The separate disposal of long-lived isotopes would not raise serious thermal or handling problems; for example, they could be deposited in a highly concentrated form into a deep geological formation

Should the waste be retrievable or not? That is ultimately a philosophical question. Which is more reliable, man or Nature? Should we trust that our descendants will have sufficient knowledge and goodwill to keep the waste safe and not misuse it—or should we rely more on Nature not to bring the waste into the biosphere by unexpected catastrophic events ?

The proposed ice-sheet disposal—be it in deep ice layers or near the surface—avoids the main dangers of both aspects. Under normal glaciological conditions the waste containers are practically irretrievable from the beginning (deep-layer deposit) or after some centuries (near-surface deposit). If, however, a catastrophic climatic change should melt away the ice sheets very quickly, the ablation melts off one after the other of the upper layers while the deep layers still remain cold. Under these circumstances the containers are “self-retrieving”: they come to the surface of (the ice or of the ice-freed bedrock and can easily be picked up. Further research on such a melt-out process and on the durability of the waste containers and their solidified contents should be carried out.
Ice Sliding and Friction Experiments
Authors: Budd W.F.
Published: September 2017

We are interested in studying the processes of sliding of ice over a variety of rock surfaces with the object of determining an empirical relation for the basal shear stress appropriate for glaciers. The variables to be considered include: normal stress Ν, shear stress Ƭ, surface roughness r, sliding velocity V, temperature θ, water at the interface, and the presence of debris. The roughness is considered to be a function of two variables; the scale or wavelength λ, and the shape or slope of the roughness a / λ, where ais the amplitude of the variations of that scale.
Formation of the Three-Layered Structure of the Amery Ice Shelf, Antarctica
Authors: Wakahama Gorow , Budd W.F.
Published: September 2017

Extensive glaciological studies on the Amery Ice Shell have been conducted since 1962 by the Australian National Antarctic Research Expeditions (ANARE). Deep core drilling to the depth of 310 m was carried out in 1968 at the site GI on the shell in order to obtain the vertical ice temperature distribution and to collect ice cores over the whole depth of the bore hole. General core analyses have been conducted since 1970 under an Australia- Japan Cooperative Project in order to clarify the structure of the ice shelf in connection with its flow.

It was found through these analyses that the Amery Ice Shelf consists of three layers of different origin, which are denoted the top, middle, and bottom layers. The top layer is formed by the in situ accumulation of snow on the shelf, the middle layer is glacier ice flowing from the Lambert Glacier, originating far inland on the Antarctic ice sheet, and the bottom layer is developed by the freezing of sea-water at the bottom surface. Numerical calculations were made of the formation processes of the three-layered structure of the ice shelf, in which the accumulation and the densification of snow at the top surface, the straining of the shelf, and the freezing of sea-water at the bottom surface were taken into account.

The thicknesses of the top and the bottom layers at site G1 obtained from the present calculations agree well with (hose obtained from the core analyses. The freezing rate of seawater at the bottom surface of the ice shelf estimated from the temperature profile is approximately 0.5 m a-1. This considerable growth of frozen sea-water at the base of the ice shelf results in water flowing out from under the ice shelf being more saline and warmer than that flowing in.
The Speed of Glacier Ization of Canada During the Wisconsin Ice Age
Authors: Mahaffy M.W. , Andrews J.T.
Published: September 2017

A three-dimensional, time-dependent numerical model of ice sheets, developed by Mahaffy (unpublished), has been applied to the general problem of the speed of ice-sheet inception and development over Canada during the last major glaciation. Ice sheet development is assumed to begin due to a lowering of the equilibrium-line altitude with a resulting increase in the accumulation over Baffin Island and Laborador in Canada. This leads to the development of large snow fields over the high plateau areas of this region. Preliminary results are given for the areal extent and the water volume of the ice sheets possible after a period of 10000 years from the initiation of glaciation.
A Movie Film Illustrating the Numerical Modelling of Periodically Surging Ice Masses
Authors: Budd W.F. , Mcinnes B.J.
Published: September 2017

A general two-dimensional numerical model for a typical flow line of a glacier or ice cap has been developed which results in periodical surging for certain ranges of the input parameters. The input includes the bedrock and surface-balance profiles along the flow line, some three-dimensional parameterization depending on the cross-section shape and the flow-line patterns, the flow properties of the ice, and a numerical basal lubrication factor.

The movie shows how a number of different ice masses grow from zero thickness to either steady state or a periodically surging state depending on the input. Typical examples of real surging ice masses from the small to the large are closely matched by the model in many effects such as the period, duration, and speed of the surges, as well as the length and thickness changes.

A preliminary study for the surging potential of a flow line in east Antarctica is also made even though the full temperature modelling is not included. The results indicate that periodic surging of the ice sheet can develop in spite of the expected high viscosity. The resultant surface profile is very similar to the measured profile. For much lower viscosities steady-state, fast-sliding, ice-stream flow develops.
Electrical Resistivity Profiles and Temperatures in the Ross Ice Shelf
Authors: Bentley C.R.
Published: September 2017

During the 1973-74 Antarctic field season, two electrical resistivity profiles were completed along directions perpendicular to each other at a site in the south-easternpart of the Ross Ice Shelf. These profiles differ from each other only at short electrode spacings (less than 10 m) indicating no measurable horizontal anisotropy below the uppermost firn zone. The shape of the apparent resistivity curves is similar to that found by Hochstein on the Ross Ice Shelf near Roosevelt Island, but is displaced toward lower resistivities despite the colder 10 m temperature (—29°C instead of —26°C) at the more southerly site. Some factor other than temperature must therefore be effective in determining the overall magnitude of the resistivities in the shelf, although the variation with depth can still be expected to be primarily a temperature phenomenon.

A computer program has been written to calculate apparent resistivities based on Crary’s analysis of temperatures in an ice shelf. Results are not yet available; when completed they should indicate the sensitivity of the resistivity measurements to differences in the temperature- depth profile, and hence their usefulness in estimating bottom melt/freeze rates.
Clathrate Ices—Recent Results
Authors: Davidson D. W. , Ripmeester J. A.
Published: September 2017

The last five years have seen an increasing interest in clathrate ices as a result of the discovery of extensive deposits of natural gas hydrates in permafrost regions. Twenty-six new clathrate hydrates have been identified, mainly by NMR, including a tetragonal hydrate of dimethyl ether. N-butane and neopentane have been found to be enclathrated in natural gas hydrates, the former as a gauche conformer. As a result of their high symmetries, encaged neopentane, CF4, SF6, and SeF6 exhibit a Resing apparent-phase-change effect in the temperature range of NMR line narrowing. There is increasing evidence that reorientational jumps of water molecules are more frequent than translational jumps in clathrate ices. This is certainly so for ethylene oxide-d4 and tetrahydrofuran-d8 hydrates for which two regions of proton line narrowing and two T1ρ minima have been observed. The reorientational motions of most guest molecules in structure II hydrates only become isotropic on a time scale long enough to permit the cage configurations to be averaged to 43m symmetry by reorientation of the water molecules. The orientations of the water molecules remain disordered to the lowest temperatures.
Interaction of Point Defects in Ice
Authors: Bilgram J. H. , Gränicher H.
Published: September 2017

The interaction of point detects in ice has been neglected for a long time. Experimental data obtained from dielectric measurements on HF-doped crystals stimulated a new evaluation of the possibility of an interaction between Bjerrum defects and ions. In a previous paper it has been shown that this leads us to assume the existence of aggregates of Bjerrum defects and ions. In this paper these aggregates and Bjerrum defects are used to explain the dielectric properties of ice, especially the temperature dependence of the product of the high and low frequency conductivity σ0σ∞.

The interaction of Bjerrum defects and impurity molecules leads to a dependence of the concentration of frenkel pairs on Bjerrum-defect concentration. At HF concentrations above the native Bjerrum-defect concentration the formation of a Frenkel pair is enhanced. This leads to the fast out-diffusion which has been studied in highly doped crystals by means of NMR techniques.
Theoretical Models for Interpreting the Dielectric Behaviour of HF-doped Ice
Authors: Camplin G. C. , Glen J. W. , Paren J. G.
Published: September 2017

To understand the recent dielectric measurements made on HF-doped ice single crystals requires a full knowledge of the concentration of electrical defects present in ice and their subsequent interactions. Previous interpretations of the behaviour of HF-doped ice have concentrated upon specific features in isolation, whereas this paper presents analyses of a data set of 139 temperature and impurity combinations from 17 HF-doped ice single crystals. The interpretation of the behaviour of these crystals is in terms of several possible theoretical models. All models are based upon the common assumptions that HF molecules enter the ice lattice substitutionally and that excess Bjerrum and ionic defects can be formed at the HF sites. They also use the theory of electrical conduction in ice by Jaccard (1959) and the defect equilibria analysis in ice by Kroger (1974).

All models yield values for the concentration, mobility, energy of formation and charges for the different types of electrical defect considered to be generated.

From the model which assumes that only three fluorine centres exist, the approximate derived values of the mobility and charge for the L-defect and positive ionic defect are as follows: μL = 5 × 10-8 m2 V-1 s-1 at 273 K, eDL = 0.44e; μ+ = 2.7 × 10-8 m2 V-1 s-1 at 273 K, e± 0.73e.

Finally, using the derived defect conductivities and the Jaccard theory of electrical conduction, the relaxation tune of HF-doped ice has been successfully predicted over a wide range of temperature and fluoride concentration.
Effect of Pressure on the Dielectric Properties of Ice Ih Single Crystals Doped with NH3 and HF
Authors: Hubmann M.
Published: September 2017

This paper describes measurements of the dielectric constant and of the conductivity on pure and doped ice single crystals subjected to hydrostatic pressure. The dopants used were NH3 (cNH3 ≈ 5 × 10-5 to 1.2 × 10-4 mol/1) or HF (cHF = 5 × 10-6 and 5 × 10-4 mol/1). The pressure and temperature ranges covered were 1 to 1 500 bar and — 15 to 60°C. The activation volumes for the orientational and the ionic contribution to the conductivity could be determined. A definitive interpretation is not possible because many questions concerning the formation of the defects are still open, hi addition to the main subject, some new data from conductivity measurements on NH3-doped single crystals at atmospheric pressure are presented.