We analyse, above continental ice, the various factors which affect the power return of the Seasat radar altimeter as measured by its Automatic Gain Control (AGC). Corrections of effects due to the AGC loop control are first applied. AGC is then normalized by positioning the half-power point at the middle of the instrument receiving window. This operation is valid for both surface and volume scattering. Over a part of Antarctica between long. 90° and 150°E., the remaining variations of AGC are of the order of 15 dB. Most of these variations occur on a large scale (>100km) and are correlated with the katabatic wind intensity. This indicates that AGC measures either surface roughness of the ice, which is related to wind intensity, or grain-size which could also be dependent on the wind. In-situ measurements support the evidence that the radar altimeter is more sensitive to surface scattering. These data could therefore provide a measurement of the intensity of katabatic winds over the continental ice.

Heat input to basal ice at subglacial low-pressure regions, such as exist on the lee side of bed bumps including regions of ice-bed separation, is shown to melt basal ice internally in a narrow boundary layer at most centimeters thick. Before ice at the ice-bed interface can begin to melt, the heat input Q must exceed a critical value Q*. Q* increases rapidly with an increase in the difference ΔΡ between the nominal (global) overburden pressure and the magnitude of the (local) normal stress acting between the ice and bed or ice and water pocket. Because of the non-linear nature of the flow law, the thickness of the boundary layer decreases rapidly with increasing ΔΡ. The ice in the boundary layer is likely to be soft with a high water content. Under certain conditions, a regelation cycle may exist between the boundary layer and the water in a subglacial cavity. The boundary layer is sufficiently narrow that the processes can reach steady state while ice traverses subglacial low-pressure regions of length the order of 0.01–0.1 m. The regelation phenomenon may preserve or aid the formation of narrow debris-rich ice layers at the base of temperate glaciers.

Crevasses, once formed, are subject to rotation and bending according to the velocity field through which they travel. Because of this, crevasse shapes can be used to infer something about the velocity field of a glacier. This is done using a model in which each crevasse opens perpendicularly to the principal extensional strain-rate, when that strain-rate exceeds some specified critical value, and is then deformed according to the same velocity gradients that formed the crevasse. This model describes how crevasses are formed, translated, rotated, bent, and lengthened.

Velocity fields are sought for which calculations produce crevasses approximating those found in three example areas on Ice Stream B, Antarctica. The first example is the hook-shaped crevasses that occur just outside the chaotic shear zone at the ice-stream margin. They are used to infer a rate of lateral shearing, and side drag. The second example, a pattern of splaying crevasses, is satisfactorily simulated by a model with side-drag stress varying linearly across the ice stream. This confirms that this region is restrained almost entirely by side drag. The third example is transverse crevasses and their change in orientation, but many different velocity fields can produce the observed pattern. Of these three examples, the shapes of hook-shaped marginal crevasses and splaying crevasses can provide useful information whereas transverse crevasses are less helpful.

The Transantarctic Mountains of East Antarctica provide a new milieu for retrieval of ice-core records. We report here on the initial findings from the first of these records, the Dominion Range ice-core record. Sites such as the Dominion Range are valuable for the recovery of records detailing climate change, volcanic activity, and changes in the chemistry of the atmosphere. The unique geographic location of this site and a relatively low accumulation rate combine to provide a relatively long record of change for this potentially sensitive climatic region. As such, information concerning the site and general core characteristics are presented, including ice surface, ice thickness, bore-hole temperature, mean annual net accumulation, crystal size, crystal fabric, oxygen-isotope composition, and examples of ice chemistry and isotopic composition of trapped gases.

The paper presents experimental observations on the growth of spongy ice in the vicinity of the forward stagnation point of a disc situated in a cross flow containing supercooled water droplets. Following some preliminary observations, the discussion focuses on two quantities: the ice fraction and the rate of growth of the accretion. The data presented reveal the effects of air speed, air temperature, liquid-water content, and salinity. They also suggest two morphological regimes: at higher air temperatures, the growth appeared to be crystalline columnar; at lower temperatures, smaller crystals appeared to be randomly distributed, producing a mushy accretion.

A hydrodynamic model of interface stability in a stratified fluid is reviewed. The model predicts that irregularities on the boundaries of a stiff layer, embedded in a soft matrix, are unstable in pure shearing flow, when compression is normal to the layer. Perturbations on such a layer can grow to form symmetric pinch-and-swell structures called boudins. The model predicts initial perturbation growth rates on the boundaries of an interglacial period ice layer. We find that, beneath an ice divide, irregularities on the Sangamon layer boundaries will not kinematically decay, as the layer thins. Finite-element modelling is used to determine the strain history of Sangamon ice beneath the divide at Summit, Greenland. That history suggests boundary irregularities have grown, relative to layer thickness, at least 26 fold over the past 90000 years. The result may be severe distortion or severing of the layer. Core holes penetrating the layer may recover anomalously thick or thin columns of ice resulting in erroneous environmental and climatic interpretations. Radio echo-sounding may be useful in searching for zones of boudinage, which should be avoided when coring. Initial perturbations might arise from mass-balance spatial variations or from transient flow fields.

The surface and bottom topography of the central Greenland ice sheet was determined from airborne ice-radar soundings over a 180 km by 180 km grid centered on the 1974 “Summit” site (lat. 72°18′N., long. 37°55′W.), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high-quality radar data were obtained, covering over 99'% of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft’s radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar-altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12% of the grid).

The highest point on Greenland is at lat. 72°34′ N., long. 37°38′W., at an altitude of 3233 ± 6 m a.s.l. The ice surface at this point divides into three sectors, one facing north, one east-south-east, and one west-south-west, with each having a roughly uniform slope. The ice divide between the last two sectors is a well-defined ridge running almost due south. The ice is about 3025 m thick at the summit. Excluding the mountainous north-east corner of the grid, where the ice locally reaches a thickness of about 3470 m and the bed dips to about 370 m below sea-level, the maximum ice thickness, approximately 3375 m, occurs about 97 km south-south-west of the summit. The average bed altitude over the entire grid is 180 m and the average ice thickness is 2975 ± 235 m. The ice in most of the south-west quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sea-level. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10–15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the south-west basin would be suitable for the drilling of a new deep ice core.

Temperatures from a bore hole through an active rock glacier in the eastern Swiss Alps are presented and thermal conditions within the slowly creeping permafrost are analyzed. Present mean annual temperature in the uppermost part of the permafrost is −3°C. Permafrost is 52 m thick and reaches heavily fissured bedrock. Thermal conductivity as determined in situ from seasonal temperature variations and measured in a cold laboratory using frozen samples is close to 2.5–3.0 W m−1 °C−1. Vertical heat flow is anomalously high (around 150 mW m-2), probably due to heat advection from circulating ground water or air within the fissured bedrock zone. Beneath this zone, which could in fact represent a non-frozen intra-permafrost layer or “talik”, relic permafrost from past centuries may possibly exist as indicated by a corresponding heat-flow inversion. Given the current temperature condition at the surface of the rock glacier and the fact that the twentieth century is among the warmest in post-glacial time, permafrost conditions may be assumed to have existed during the whole of the Holocene and, hence, during the entire time of rock-glacier formation.

Digital terrain models (DTM) are a very important tool for all sorts of glacier studies and serve as a basis for many applications. The latest development is the combination of DTM with digital image-processing techniques which enable a much better visualization of the DTM, and thus a better interpretation of glaciological phenomena.

These new technologies have been applied in an investigation of the Vaughan Lewis Icefall, Juneau Icefield, Alaska. A DTM has been produced by means of photogrammetrie measurements, and a glacier-flow velocity of up to 5.70 m d−1 in the steepest part has been derived. The possibilities for the interpretation of the glacier topography have been significantly improved by using digital image-processing algorithms for the visualization of the DTM.

This study investigates the processes of ice-marginal sedimentation in Vestfold Hills, Antarctica. Most debris is released from the ice when basal and englacial debris bands become warped and reach the surface of the glacier and where the debris bands are exposed by ablation of the ice surface. Once released, the debris is redistributed in the ice-marginal area by depositional processes that are controlled by the availability of water. During the short summer, melt water from snow and ice saturates the newly released debris and causes sediment flows and other mass-movement deposits. Melt-out and sublimation tills form after the layer of debris on the moraines is consolidated and melting rates decrease. When the thickness of deposits on the surface of ice-cored moraines reaches or exceeds the depth of summer thawing, the ice core no longer melts and the moraines become semi-permanent features. The sediments and land forms of the ice-marginal area closely resemble those formed by sub-polar glaciers with a complex thermal regime and are unlike those that form at the margins of dry-based polar glaciers. Although glacier thermal regime is understood to be a major control on debris dispersal and processes of glacial sedimentation, the evidence from Vestfold Hills suggests that the primary control is the climate of the glacier terminus area.

Two seismic arrays recorded in an 11 month field experiment in 1985 the seismicity of Ekström Ice Shelf in the area of an ice rumple and an inlet, situated respectively about 10 km north-west and 7 km north of the German Antarctic station Georg von Neumayer (lat. 70°37′S., long. 08°22′W). Most of the focal depths of the icequakes considered until now are in the range 5–9 m; the ice-rumple area shows extremely high seismic activity. Tensile fracture is the most frequent fault mechanism, although there are a few shear-fracture events. The ice rumple’s seismicity provides information on the dynamics of the ice shelf in this area. A comparison of this time-dependent seismicity with tides suggests that most of this seismicity is induced by tides. The most active period of this seismicity starts at the beginning of low tide and ends at low tide. The location of the epicentres of icequakes recorded at that time and the digital recording on tapes of the seismicity without interruption for 396 h shows a jerky vertical movement of the ice shelf in response to tides; this can be interpreted as a kind of “grater effect”, especially at the southern ice-rock boundary of the ice rumple.

The seismicity in the inlet is much less and tensile fracture seems to be the only fault mechanism.

Bualtar Glacier, Karakoram Range, northern Pakistan, surged during the spring and early summer of 1987. This followed a major episode of three landslides which impacted part of the glacier ablation zone on 30–31 July 1986. In May 1987, surface velocities of 7 m d−1 were measured at one profile down-glacier from the landslide deposits, where in 1986 velocities were an order of magnitude less. Surface and hydrological characteristics of the glacier in and down-glacier from the landslide deposit were also indicative of surge-like behavior in 1987, and a return to pre-surge conditions by 1988.

Drilling bore holes in deep, cold ice masses by hot-water methods and maintaining these holes with sufficient diameter to allow down-hole experimentation poses a major obstacle to the investigation of conditions beneath ice sheets and ice streams. Closure of the water-filled holes by refreezing is the dominant difficulty. In this paper, we describe calculations of heat transfer from the drilling system to the ice and the subsequent time-dependent motion of the phase boundary defining the bore-hole wall. Results are presented with the view of optimizing the bore-hole radius at depth for a fixed drill performance and a variable rate of drilling.

Calculation of melting/refreezing rates at the bore-hole wall requires the use of a one-dimensional, time-dependent numerical heat-flow model with a distorting mesh which follows the changing hole size. The delay of hole closure is discussed with a view to keeping holes open long enough to allow instruments to be lowered to the glacier bed, while realizing that drilling-system performance may be marginal because of logisitical and/or expenditure constraints. The relative merits of drilling a large hole, which is very time consuming with a small drill, and the use of water-soluble antifreezes, which have a history of creating plugs of ice slush, are discussed. A method of creating a stable hole filled with antifreeze in which ice slush does not occur is described.

The recent application of these theoretical ideas to the planning and implementation of successful hot-water drilling programs in Antarctica and Greenland is also presented.

In spring and winter, there is a considerable amount of solid precipitation in the western part of the Tian Shan mountains. Avalanches frequently occur here, and often endanger national economic construction and human life. Observation shows that the avalanche occurrences are closely related to the physical characteristics of the snow, especially to the development of depth hoar in the snow cover. The conditions for the development of depth hoar are determined by thickness of the snow cover, air temperature, ground-temperature regime, and the duration of negative temperatures. The results of this study have revealed that the optimum depth of snow cover for the development of depth hoar is about 80 cm in the Tian Shan mountains, and the mean maximum depth of the snow cover in this region is 78 cm. Therefore, depth hoar develops extraordinarily well. The thickness of depth hoar can reach more than 80% of the total snow-cover depth. That is one of the main reasons why avalanches still occur frequently under the conditions of a limited snow-cover depth in the western part of the Tian Shan mountains.

The deep-drilling projects at the Summit ice divide will require thermal models to help interpret the paleoclimatic signals in their cores. An analytic, steady-state model predicts basal temperatures within 1 °C of the ice melting-point and basal ice no older than 100–400 kyear should melting occur. A two-dimensional, time-dependent temperature model includes the effects of realistic two-dimensional ice flow and the temperature and mass-balance patterns of the last two glacial cycles. The model relaxes some assumptions made in one-dimensional studies and produces lower basal temperatures. The basal temperatures are most sensitive to the value of the geothermal heat flux and the mass-balance pattern. If the flux is less than 56 mW m−2, the bed has likely been frozen throughout the last glacial cycle. The decoupling of the energy and mass-conservation equations is a significant source of error which can be eliminated only by a fully coupled ice-flow/ heat-flow model.

The growth of two-dimensional, or laterally confined (flume), aufeis is shown from laboratory data to depend primarily on seven, independent, dimensionless parameters. During the early, two-dimensional, phase of its growth, aufeis consists of a mixture of ice and water, or ice-water slush, forming on a frigid base. Its early growth depends on four parameters: those expressing position along aufeis, period of spreading, slope of frigid base over which aufeis forms, and magnitude of heat flux to air from the surface of aufeis relative to latent heat release during freezing. The influences of two of the three remaining parameters, those expressing magnitude of heat flux to air relative to heat flux to frigid base and confined width of aufeis growth, are not felt until after a transition time has passed. The transition time apparently coincides with the beginning of the processes by which the ice-water slush on the surface of aufeis freezes solid. After a slush layer on aufeis begins to freeze solid, a new slush layer forms over its frozen surface. The continuing, cyclic process by which slush layers form and eventually freeze results in the ice laminations that are a feature of aufeis. The influence of the seventh governing parameter, a Reynolds number, cannot be discerned in the laboratory data.

Air content (V) of polar ice has been used as an indicator of the past elevation of the ice sheets. A calculation is presented to correct V measurements performed on ice samples for the effect of cut bubbles at their surface. The results indicate a correction ranging from 1 to 10% for cubic ice samples with about 3 cm length. The correction depends mainly on the size of the bubbles. The theoretical calculation is experimentally verified. The statistical noise linked with the presence of a finite number of bubbles in the ice samples is evaluated. The influence of such a correction on the V profiles measured on polar ice cores is discussed. The method in this paper can also be used for correction of ice-density data obtained by the hydrostatic method.

Freezing processes in temperate ice consisting of a mixture of pure ice with water inclusions are studied for the case that the initial amount of moisture content is uniform. By introducing a cold source at the center of the ice specimen, the cold front propagates outwards leaving behind pure cold ice with a temperature distribution dictated by the exact set-up of the cold source. The speed of the front is directly related to the water content of the temperate ice and depends essentially on the Stefan condition.

Three types of initial and boundary conditions are considered and realized in uniaxial, cylindrical, and/or spherical symmetry: (1) a metallic core at a temperature below the freezing point is initially brought into contact with the ice and the system is left free to evolve; (2) the metallic core is kept at constant temperature below freezing; (3) Case (2) is repeated with an insulating air layer between the metallic core and the ice.

Two-dimensional finite-element calculations of velocity and temperature fields have been applied to the energy balance of a cross-section of Barnes Ice Cap, Baffin Island, Canada. The flow plane currently is cooling near the ice divide and warming near the margin. Long-term simulations show a net warming trend followed by a cooling trend with a steady-state average temperature similar to the present. Sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface-temperature forcing, because a negative feedback in temperature advection is substantially larger than a positive feed-back in strain heating. The response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one-dimensional modeling. When bedrock-temperature calculations are included, response times increase an order of magnitude, but these do not substantially affect the short-term response.

Glacial abrasion was simulated in experiments in which a small artificial glacier bed was pushed beneath a fixed ice block under pressure. The experiments provide a means of testing theoretical models of abrasion, particularly those factors that govern the magnitude of stress concentrations beneath abrading rock fragments. In preliminary experiments, vertical ice flow around a sphere mounted on the bed was studied. In subsequent experiments, marble tablets were pushed beneath granitic rock fragments frozen into the base of the ice block. Unlike previous abrasion experiments, the sliding velocity was realistic (25 mm d−1), and ice near the bed was at the pressure-melting temperature. Resultant striations closely resemble those observed on glaciated bedrock.

As predicted by Hallet (1979), the component of the ice velocity towards the bed strongly influenced stresses beneath fragments, and classical regelation and creep theory provided an approximate estimate of the downward drag force on fragments. Half of the rock fragments rotated significantly, accounting for 10–50% of their motion relative to the bed and influencing abrasion rates and the shear stress supported along the ice-bed interface. Striation patterns indirectly suggest that fragment rotations were inhibited by increases in ice pressure, which presumably increased the drag on roughness elements on fragment surfaces. This may have resulted from a reduction in the thickness of the water film around fragments, facilitated by leakage of water from the bed.