Geomechanical rock-mass properties control the response of bedrock to applied stresses and can be summarized in a linear Mohr-Coulomb equation, which defines the principal parameters determining failure. Nevertheless, in studying the erosion of bedrock by glacier ice, little attention has been paid to failure criteria though a coincidence of erosion all and forms with fracture systems at regional and local scales has been demonstrated. Few studies have analysed the precise nature of the fracture geometry, or proposed its mechanical impact in association with glacier ice.

This investigation proposes that, since almost all bedrock possesses identifiable fracture systems, the properties of discontinuous rock mass (DRM) be regarded as defining primary conditions of stress and stability which are subsequently modified directly and indirectly by glacier ice. Consequent rock-mass failure modes are prescribed by discontinuity geometry and applied stresses, and evidence from North Wales confirms the validity of the theoretical treatment of rock-mass properties, and explains the accordance of landforms with structure.

Electrical conductivity of melt waters draining from the portal of Gornergletscher, Switzerland, was recorded continuously for extended periods during the 1978‐79 hydrological year. Conductivity was used as a surrogate measure of the total dissolved solids concentration in melt water to describe the seasonal variation of solute, and its relation to discharge, in an attempt to use melt-water hydrochemistry as an indicator of the nature of subglacial processes within an alpine glacier. In winter, conductivity was 2 to 10 times higher than during the summer ablation season. and also showed considerable diurnal and annual variations independent of discharge. The transition from winter to summer discharge regime was preceded by falling solute concentration. A distribution shaped as a “triangle-with-spike” describes the complex relationship between discharge and electrical conductivity for the annual cycle of run-off. Almost all the solute load from beneath Gornergletscher is evacuated during summer. Melt-water hydrochemistry provides some insight into the nature of sub-glacial chemical processes, but, since melt waters do not appear to have access to all areas of the glacier bed, it probably under-estimates total chemical activity.

Ice-thickness and surface-elevation data gathered from radio echo flights over the Antarctic Peninsula are presented as profiles for five major outlet glaciers in northern Palmer Land and as contour maps for an area of 8 000 km2 to the east of George VI Sound. Glacier profiles appear to be closely related to ice discharge especially to convergent and divergent flow. Comparison of subglacial topography with geological evidence of faulting suggests that the area around George VI Sound is a region where structure is an important influence on the pattern of glacial erosion.

A model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice-rock interface on glacier sliding. An increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed. Abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content. A similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness. Sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed.

The existence of cold patches at the base of a glacier suggests that the sliding law will depend on these patches, which will essentially affect the viscosity constant. In a poly thermal glacier, such as a glacier which is cold in its lower part and temperate in its upper part, basal boundary conditions change from no-slip to viscous sliding. It is anticipated that the viscosity constant of this sliding law will depend on the distance from the transition line between cold and temperate ice.

The mixed boundary conditions, namely no-slip where the ice is cold and viscous sliding where it is temperate, induce large stresses and velocity changes close to the transition line. In fact, it is shown that, for a Newtonian fluid and all investigated discontinuities of boundary data, square-root singularities of the stresses will develop at the transition line. Asymptotic expressions for the basal stresses are derived. The explicit forms of these asymptotic expansions depend on the form of the spatial dependence of the sliding law and, furthermore, on the numerical values of the viscosity coefficient. It is, moreover, argued that the stress concentrations are sufficiently pronounced to account for the removal of basal rock especially in regions of high cleavage concentrations, the details again depending upon the sliding coefficients.

No mathematical details of the problem solved are presented as attention is focused on the physical processes.

35 mm still and television techniques are shown to be of great value in following changes at the bedrock/ice interface and along borehole walls during closure over one or more years in polar or sub-polar ice caps. We have found no evidence of basal slip over a one year period in a 137 m hole at the top of the flow line on an ice cap in northern Ellesmere Island, However, the bore hole has deformed to an elliptical cross-section near the bed and some pronounced extrusion-like layers have developed within 3 m of the bed in dirty ice in the year since drilling.

A comparison is made of silt-particle size and shape, and of boulders, from supraglacial, englacial, and subglacial locations of Roslin Gletscher in east Greenland, Findelengletscher* in Switzerland, and fragments of laboratory ground sandstone. Particle roundness increases as size decreases in each zone of both glaciers. Roundness increases similarly for silt and for boulders from the supraglacial to the subglacial zone. Elongation expressed as width-to-length ratio has a mean value of 0.67 ± 0.17 which persists through a wide range of silt and boulder sizes. Crushing into smaller pieces, rather than the removal of asperities, is postulated as the dominant process of glacial erosion. Sediment loads are given for the glacial streams.

Results are given of radio echo‐sounding of 53 glaciers of different sizes and glaciological regimes during 1974–75 and 1977–79 in Spitsbergen. Mountain glaciers have maximum ice thicknesses ranging from 90 to 350 m. Thicknesses up to 165 m, as well as the presence of overdeepened sections of the bed and subglacial ridges up to 100 m high are typical. Other glaciers have ice thickness values of up to 500 m (e.g. Veteranen) but on some sections of glaciers and ice caps depressions in the bed with ice thicknesses reaching 540 m have been found, which exceed the “background” thickness by 200 to 400 m. Subglacial relief of Vestfonna, Nordaustlandet, is very rough in its outer region but is rather smooth in the central part beneath the ice dome, where ice thickness reaches 385 m. Multiple correlation analysis of 15 glaciers indicates a number of significant relationships between the area of terminal and lateral moraines of glaciers and length, area, and, consequently, volume.

Recent studies have shown the important influence of pore-water movement and the subglacial thermal regime on processes of erosion and deposition at the subglacial interface. the influence of migrating freezing fronts within subglacial material has been largely ignored. the phenomena of ice-water interface processes will be examined and their relevance to subglacial processes illustrated. four case studies are presented that deal with the various effects that freezing-front movement may have on pore water, consolidation, shear strength, and likely diagenetic characteristics of subglacial deposits. the influence upon erosional and depositional processes will be outlined, and a mechanism related to potential surge-like conditions within the subglacial zone postulated.

A rapid displacement of glaciers occurs at times when the water supply from melting or lake drainage surmounts the capacity of the subglacial drainage system. It is explained by the hydraulic action of water at high pressure in cavities which open up on the lee side of undulations or steps of the glacier bed. It is suggested that, because of pressure-induced temperature fluctuations, rock fragments may freeze on to the glacier sole and be lifted out into an opening cavity. Laboratory experiments have shown that small pressure fluctuations of a few bars* only are sufficient for rock slabs of a considerable thickness to be moved in this way.

The basal ice layer of Glacier de Tsidjiore Nouve in the Swiss Alps consists of debris bands and associated clear ice lenses. This layer is due to refreezing of squeezed water at the sale of the glacier, as evidenced by the chemical properties of the ice. Active erosion processes include entrainment of debris in the basal ice layer and abrasion on rock protuberances immediately down-glacier. The formation of the basal ice layer requires that the temperature of the squeezed water, which is determined by the pressure-melting point within the basal ice, should be below the freezing temperature of the pore water in the subglacial debris layer. This would be the case if the pore water were at a pressure lower than the basal ice pressure.

Mercury is used to force a block of ice, measuring 0.20 ⨯ 0.45 m in area and 0.20 m in height, over an irregular bed. Normal and shear stresses on the bed can be varied up to 15 and 3 ⨯ 105 Pa respectively, so the apparatus permits a full-scale simulation of sliding of a 150 m thick glacier over irregularities a few tens of millimeters in height.

Preliminary results of an experiment in which ice slid over a bed consisting of two streamlined bumps, roughly 15 mm in height, suggest that sliding velocity is independent of normal pressure in the absence of cavitation. This is consistent with existing theoretical models of glacier sliding (Weertman 1964, Kamb 1970, Lliboutry 1979), but is not consistent with the experimental results of Budd and others (1979). Further studies are needed to determine the reasons for this disagreement.

The relationship between bedrock erodibility and the characteristic bed form and roughness produced by subglacial abrasion is largely unknown. Less resistant bedrocks may be abraded down to a surface of low obstacle size and low roughness parameter. However, Hallet (1979) notes that bedforms are probably dampened at widely varying rates, and that certain bedforms may actually be amplified through time by rapid trough abrasion. The object of this paper is to examine the relationship between the mechanical strength of several bedrock types and the magnitude of subglacially streamlined bed forms found on them.

Cambrian limestones, mudstones, dolomites, and chert, some with abundant quartz veins, are the bedrock types examined. They lie as a series of steeply-dipping beds up to 100 m thick with their strike across the floor of the Yoho valley, in the Rocky Mountains of British Columbia. They were covered by the ice of Yoho Glacier 30 years ago, and are now less than 0.5 km below the present ice terminus. The sites examined lie within an area less than 0.25 km2, up-glacier from a major riegel form. The Yoho River nearby flows in a deep gorge and has not affected this section of the former glacial valley floor.

The bedrocks were analysed and tested in the laboratory for mechanical strength and resistance to abrasion.

During summer 1979, streamlined bedforms and surface roughness were surveyed along the former glacier flowline, evidenced by striations, and plane table maps were completed across several beds. Small 1 m2 plots were surveyed in detail on each bedrock type. Analysis of surface forms has included 3-dimensional SYMVU plots. Preliminary indications are that the micro-roughness shows greater variability between bedrock types than do large wavelengths of relief. However, resistant bedrocks are areas of prominent positive relief while others are generally low-lying. Analysis of the results continues.

Experimental data from several Soviet authors are used to investigate the importance of relief-forming processes in a glacial environment. Water discharge from glacial rivers was found to be crucial for the evolution of frontal moraines versus pro-glacial glaciofluvial deposits (sandar and valley trains).

Mýrdalsjökull is a temperate ice cap with an area of 596 km2, covering the volcanic Katlamassif in southern Iceland. Since 1900, extensive areas of ground moraine have been exposed during glacier retreat along the northern margin of the ice cap. The ground moraine surface is characteristically covered by a coarse layer of rock particles 10 to 150 mm in size. At the present glacier front, particles of corresponding size can be seen melting out from the lowermost glacier ice. Samples of ice and debris were collected from the basal transport zone. here generally 20 to 50 mm thick. and the volume, grain size, shape, and surface texture were determined. The orientation of rock particles in the englacial position. in the basal transport zone, and in the under lying lodgement till were analysed. The rock particles that dominate the debris content in the basal transport zone and constitute the coarse surface layer beyond the glacier margin are interpreted as a residual, which has escaped subglacial frictional deposition.

The origins of diamictons deposited at the Matanuska Glacier are identified in stratigraphic sequences mainly by the presence or absence of a pebble fabric, internal structure, and variation in gravel-size clast distribution. These properties correlate with major differences in depositional mechanisms and source material. Melt-out till mostly inherits fabric, internal structure, and grain-size distribution from its debris-laden basal ice source. Sediment flow deposits and ice-slope colluvium (deposited by ablational slope processes) have properties developed by resedimentation mechanisms. Melt-out till ranges from structureless to stratified with interspersed lenses and discontinuous laminae, and generally possesses a well-defined pebble fabric. Sediment flow deposits show various combinations of six sedimentologic units with distinct sedimentary features and clast dispersion. Pebble fabric is absent or poorly defined, depending upon the unit's origin. Ice-slope colluvium is usually featureless, except for randomly-dispersed laminated lenses and irregularly-shaped gravelly zones in an otherwise disarrayed assemblage of particles, and is without a pebble fabric.

Ablation of glacier ice has been observed with artificial debris layers prepared with Ottawa sand (ASTM C-109) ranging from 0.01 to 0.1 m thick. Data on external variables observed during the experiments and determination of physical constants of the debris layers have allowed the testing of a proposed simple model. Theoretical predictions compare favourably with the observations. Discussion is extended to a proposal for a simple method by which ablation under a debris layer could be estimated even if the thermal conductivity or thermal resistance of the material were unknown.

A question is posed regarding the source of melt-water sediment. Does stagnant ice, functionally separated from active ice and gradually melting in place, contain enough rock debris to account for the volume of melt-water deposits known to exist in deglaciated areas, or does the volume of these deposits require a sediment source in close association with active ice from which the supply of rock debris is continually replenished?

Differing opinions on this question are implied in two contrasting models for deglaciation in the north-eastern United States. One, involving regional stagnation, assumes a sediment source in stagnant glacier ice; the other, involving stagnation-zone retreat, considers active ice the principal sediment source. This paper presents reported values of debris content in glacier ice and uses these values to calculate theoretical sediment volumes for a small drainage basin (1 300 km2) in northeastern U.S.A.

A typical value for the amount of rock debris in temperate glacier ice is 25% (volume) debris content in a 400 mm-thick basal debrisrich zone. This value gives a calculated sediment volume of 0.13 km3, about 6% of the estimated actual volume of melt-Hater sediment in the test basin. Comparison of calculated theoretical sediment volume with the estimated actual sediment volume in the basin indicates that stagnant ice is an inadequate sediment source, and that active ice, rather than stagnant ice, is probably the principal sediment source for melt-water deposits.

Casa Pangue glacier is a regenerated valley glacier, covered by supraglacial moraine of variable thickness (1 to 3 m). Seven moraine in-transit arcs have originated from avalanches falling on the ice from the steep walls at the head of the valley. The debris has been relocated by glacier movement, and vegetation has become established on areas with sediment cover. Primitive soil has developed very rapidly, probably in less than 100 a. Chemical analysis of soil samples show that it is acid (pH 4.6 to 4.7), nitrogen and organic matter are absent, calcium content is low, and potassium content is high. Pedogenic processes are mostly related to intense chemical weathering, under conditions of more than 4 000 mm a−l of total precipitation.

The plant communities established on the moraine are essentially similar to the Va1divian rain forest that characterizes the region. The most frequent tree is “coihue” (Nothofagus dombeyi), followed by “teniú“ (Weinmannia trichosperma) and “notro” (Embothrium coccineum). One specimen of N.dombeyi was found to be 18 m tall and 0.62 m in diameter; many others were taller than 12 m and reproduction was abundant. Dendrochronological analysis indicates a minimum age of 45 a for the oldest tree. Other plants found here are shrubs, some hemiparasitic and creeping plants, mosses, lichens, ferns, and fungi.

Using air photographs of 1942, 1953, 1970, and our own oblique photographs of 1978, taken from the summit of a neighbouring peak 1 200 m above the glacier tongue, average surface velocity of the glacier tongue was estimated at 22.5 m a−l for the lower and intermediate sectors where the trees are growing. If the total length of the regenerated valley glacier is taken into account, the mean annual movement rate is 35.0 m a−l. If this value is extrapolated over the last 45 a, the trees have moved an average distance of at least 1 000 m in that time.

The discovery of established communities (also observed at Río Blanco glacier, southwest of Mt Tronador) on moving ice constitutes an event not previously recorded in glaciological literature. Some significant aspects are discussed: time lapse for soil development on moraine deposits, primary plant succession on moraine deposits, the need of stable ground for plant colonization, the absolute validity of radiocarbon dating of glacier advances using fossil wood found within terminal moraines, and the validity of lichenometric techniques in deglaciated terrain.