In the summers of 1993, 1994 and 1995, video and Global Positioning System location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the Bering Glacier and Bagley Ice Field system (Alaska) in an effort to characterize surge-crevasse patterns and surge propagation. During survey flights in late August 1995, we observed that the 1993–94. Bering Glacier surge was continuing and still expanding affecting new areas farther up in Bagley Ice Field. New crevasse fields, similar in pattern to the first surge crevasses we had observed in June 1993 below Khitrov Hills and in other isolated areas of central Bering Glacier and in July 1994 near the head of Bering Glacier (near the junction of Bering Glacier and Bagley Ice Field, in both upper Bering Glacier and Bagley Ice Field), were opening in eastern Bagley Ice Field and in the “Stellet” side of Bagley Ice Field. The type of crevasses seen in the new fields suggested that the surge was propagating into these areas. By analysis and interpretation of the brittle-deformation patterns apparent in the crevasse patterns, some aspects of the past kinematic framework of the surge can be deduced. This approach may lead to a more general classification of ice-surface structures and to their linkage to ongoing processes.

Effects of the retreat of Gåsbreen, southwest Spitsbergen, Svalbard, on the evolution of the ice-dammed lake Goësvatnet are shown for the period 1899-1991. The retreat and lowering of the damming ice masses have changed not only the stored lake volume, the lake geometry and the elevation, slope and length of the subglacial outlet tunnel, but also the frequency and magnitude of outburst floods of Goësvatnet. For the estimation of peak discharges of outburst floods we computed an unbiased regression equation related to the progressive enlargement of subglacial tunnels using lake volume data and peak discharge data from the literature. The derived equation is very similar to the original form of the Clague-Mathews formula and answers the question why this formula has worked well in many cases. Peak discharges of Goësvatnet in various years were estimated by means of the derived equation. Effects of the changed lake geometry as well as the changed length and slope of the subglacial outlet tunnel on the discharge during outbursts will be discussed by means of the Nye-Clarke model. Observation of an outburst of Goësvatnet in summer 1991 indicates that the outbursts may have been triggered by pressure decrease in the subglacial outlet tunnel during increased discharge, whereas flotation of the ice dam can be excluded.

The flow field of a medium sliding without friction over a strongly undulating surface is calculated numerically. The results are used to elucidate the basal-flow characteristics of glacier flow and they are discussed with reference to known analytical solutions. Extrusion flow is found to become increasingly pronounced as the value of n, where n is a parameter in Glen’s flow law, becomes larger. For sinusoidal bedrock undulations, a flow separation occurs if the amplitude-to-wavelength ratio exceeds a critical value of about 0.28. The main flow then sets up a secondary flow circulation within the trough, and the ice participating in this circular motion theoretically never leaves it. The sliding velocity is calculated numerically as a function of the mean basal shear stress, the amplitude-to-wavelength ratio and the flow parameter n. For moderate and high slope fluctuations, the sliding velocity is significantly different from what would be expected from results based on the small-slope approximation.

This article aims to give a comprehensive view of the distribution patterns for natural and artifical radionuclides over Antarctica. We focus this study on 137Cs, 210Pb and tritium. Applying various statistical methods, we show that the deposition of radionuclides reveals a structured distribution, although local drift redistribution and the snow-surface roughness disturb the representativeness of samples and produce a “noise” effect. The deposition of 137Cs over Antarctica (885 TBq) represents 0.09% of the total deposition of this radionuclide in the world and the correlation between 137Cs fluxes and accumulation shows two sub-populations. For the stations with a mean annual temperature above −21° C, a strong correlation is found, whereas the correlation is lower for locations with temperatures below −21° C. The flux of 210Pb varies from 0.9 to 8.2 Bq m −1 a−1 with values strongly correlated with the accumulation and a well-defined spatial structure. The same mechanism governs the deposition of artificial and natural tritium but it clearly differs from that of other radionuclides associated with particulate material. The “dry fall-out” accounts for between 60 and 80% of the total fall-out for the artificial radionuclides and around 40% for 210Pb. This difference is likely related to a tropospheric fraction for 210Pb. Despite its isolated location, the radioactive fall-out of artificial long-lived radionuclides over Antarctica has been ten times greater than for natural radionuclides.

The evolution of ice-sheet configuration and flow pattern in Fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model, i.e. a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets. The model uses mapped flow traces and deglacial melt-water landforms, as well as relative chronologies derived from cross-cutting striae and till lineations, as input data. Flow-trace systems were classified into four types: (i) time-transgressive wet-bed deglacial fans, (ii) time-transgressive frozen-bed deglacial fans, (iii) surge fans, and (iv) synchronous non-deglacial (event) fans. Using relative chronologies and aggregation of fans into glaciologically plausible patterns, a series of ice-sheet Configurations at different time slices was erected. A chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume. Geological evidence exists for several discrete ice-sheet configurations centred over the Scandinavian mountain range during the early Weichselian. The build-up of the main Weichselian Fennoscandian ice sheet started at approximately 70 Ka, and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern Norway. This configuration had a flow pattern which is poorly reproduced by current numerical models of the Fennoscandian ice sheet. At the Last Glacial Maximum the main ice divide was located overthe Gulf of Bothnia. A major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the Scandinavian mountain chain. Widespread areas of preserved pre-late-Weichselian landscapes indicate that the ice sheet had a frozen-bed core area, which was only partly diminished in size by inward-transgressive wet-bed zones during the decay phase.

Genetic classification of glacial deposits still proves to be highly controversial. In many cases, it remains unclear whether a particular sediment has been sub-glacially deformed. In the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations. It is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism. Deformational mechanisms associated with the fracturing process are outlined and explained, using a series of thin sections from Wijnjewoude, The Netherlands.

Poor consideration has been given in many Arctic circum-polar ice-core studies to the effect of summer snow melt on chemistry, stable-isotope concentrations and time-scales. Many of these corps are drilled close to the firn line where melt is intense. Some come from below the firn line where accumulation is solely in the form of super-imposed ice. In all cases, seasonal signals are reduced or removed and, in some, time gaps develop during periods of excessive melting which situate the drill site in the ablation zone. Consequently, cross correlations of assumed synchronous events among the cores are invalid, so that time-scales along the same cores differ between authors by factors of over 2. Many so-called climatic signals are imaginary rather than real. By reference to published analyses of cores from the superimposed ice zone on Devon Ice Cap (Koerner, 1970) and Meighen Ice Cap (Koerner and Paterson, 1974), it is shown how melt affects all the normally well-established ice-core proxies and leads to their misinterpretation. Despite these limitations, the cores can give valuable low-resolution records for all or part of the Holocene. They show that the thermal maximum in the circum-polar Arctic occurred in the early Holocene. This maximum, effected negative balances on all the ice caps and removed the smaller ones. Cooler conditions in the second half of the Holocene have caused the regrowth of these same ice caps.

A new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1 at GRIP to 0.19 m ice equivalent year−1 50 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

The varying ice extent on the Kibo cone of Kilimanjaro, East Africa, this century was reconstructed from terrestrial-photogrammetric mappings in 1912 and 1953 and satellite images in 1976 and 1989. These were all conformed to the official 1:50 000 topographic sheet. The ice distribution on Kibo is characterized by lower ice margins on the southern than on the northern flanks, and deepest-reaching glaciers to the west contrasting with least ice cover on the eastern crater rim. The meridional contrast appears to be related to the more abundant precipitation on the southern side. The even more striking zonal asymmetry in ice cover is favored by the vigorous diurnal circulations, with enhanced afternoon cloudiness blocking insolation on the western slopes. The total ice cover diminished from 12058 to 6675 to 4171 in 3305 × 103 m2 between the years 1912,1953, 1976 and 1989, and the three large coherent ice bodies disintegrated into numerous smaller ice fragments.

Changes along the margin of the southern half of the 5900 km2 Barnes Ice Cap have been assessed using 1993 Landsat TM imagery in comparison with digitized 1:50 000 NTS maps based on 1961 photogrammetry. The average recession over the 183 km long southern perimeter was found to be at least 4 m a−1, with no significant difference between the southeast and southwest sectors. Viewed in conjunction with the sustained retreat previously reported for the northwest margin, these results indicate that a general reduction in the size of Barnes Ice Cap is occurring. The present retreat phase began under a regional climate warming in the late 19th to early 20th century period and continues, while the record of the ablation-season temperature since the mid-century has not shown any significant trend.

The three-dimensional ice-sheet model SICOPOLIS is used to simulate the dynamic/thermody namic behaviour of the entire Greenland ice sheet from 250 000 a BP until today. External forcing consists of a surface-temperature history constructed from δ18O data of the GRIP core, a snowfall history coupled linearly to that of the surface temperature, a piecewise linear sea-level scenario and a constant geothermal heat flux. The simulated Greenland ice sheet is investigated in the vicinity of Summit, the position where the maximum elevation is taken, and where the two drill sites GRIP and GISP2 are situated 28km apart from each other. In this region, the agreement between modelled and observed topography and ice temperature turns out to be very good. Computed age-depth profiles for GRIP and GISP2 are presented, which can he used to complete the dating of these cores in the deeper regions where annual-layer counting is not possible. However, artificial diffusion influences the computed ages in a near-basal boundary layer of approximately 15% of the ice thickness, so that the age at the bottom of the cores cannot be predicted yet.

The mechanical interaction between a glacier and subglacial sediment can be observed using an instrumented rod that we refer to as the UBC ploughmeter. For clast-rich sediments, the rate of collision between clasts and a rod dragged through these sediments should be related to the glacier sliding rate. By assuming that proglacial measurements of sediment granulometry represent the subglacial granulometry of Trapridge Glacier, Yukon Territory, Canada, we have used ploughmeter results to obtain an estimated sliding rate of ∼45 mm d−1, in good agreement with known rates. In addition, for a subglacial material treated as a solid-liquid dispersion having a linear viscous rheology, the force of collision experienced by the rod should be proportional to the effective sediment viscosity. Our estimate of ∼2.0 × 1010 Pa s agrees well with previously, derived values.

Response tests are widely used in ground-water studies to assess the hydraulic properties of sub-surface water-flow systems. The simplicity of such tests also makes them attractive for investigation of subglacial hydraulic conditions. This paper describes a systematic, quantitative approach to the analysis of borehole-response test data. The approach uses the theoretical model of Stone and Clarke (1993), which describes water motion in a coupled borehole—subglacial flow system; this framework provides the basis for an inversion scheme that is focused on quantifying physical properties of the basal-flow system, as it is characterized in the theoretical model. The inversion procedure was applied to response-test data from Trapridge Glacier, Yukon Territory, Canada. Results of the inversions suggest that the subglacial drainage network can be described as a confined layer comprising coarse-sand-to fine-gravel-sized sediments, having a thickness of 0.1 – 0.3 m, and a hydraulic conductivity of about 5 × 10−4ms−1. Based on the water-drainage rates from boreholes, as they connect with the subglacial water-flow system, specific storage of the sediment layer was estimated to be approximately 1 × 10−4m−1. Further consideration of subglacial water-flow conditions suggests that connection drainage test results may tend to underestimate specific storage of the overall glacier substrate.

Active tectonism in the Himalaya, and the long-fault lineament controlling the east–west river valleys, play an important role in melt at the snouts of glaciers, or their fluctuations during the year. Lower glacier limits are controlled by high winds from the Indian plains flowing along the valleys. Fluctuations of the Chhota Shigri glacier depend on temperature variations at the junction with the Chandra River valley and in the unconsolidated morainic debris below the glacier ice. High flow rates in the ablation zone indicate that basal sliding is the main movement mechanism. Melt takes place mainly from advection, and this process of melting during the summer season occurs both day and night.

Satellite imagery indicates that the floating terminus of Pine Island Glacier has changed little in extent over the past two decades. Data on the velocity and thickness of the glacier reveal that calving of 28 ± 4 Gta−1 accounts for only half of the ice input near the grounding line. The apparently steady configuration implies that the remainder of the input is lost by basal melting at a mean rate of 12 ± 3 ma−1. Ocean circulation in Pine Island Bay transports +1°C waters beneath the glacier and temperatures recorded in melt-laden outflows show that heat loss from the ocean is consistent with the requirements of the calculated melt rate. The combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin, drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet.

Observations are reported on cracks formed during compressive, unidirectional, constant-strain-rate deformation of columnar-grain ice. The axis of hexagonal crystallographic symmetry of each grain tended to be in the plane perpendicular to the long direction of the grains and to have a random orientation in that plane. For stress applied perpendicular to the long direction of the grains, the deformation was practically two-dimensional. It was found that the relative proportion of grain-boundary cracks increased with increasing strain rate, decreasing temperature and, for strain rate greater than 7 × 10−5 s−1, with decreasing grain-size. Almost all the grain-boundary cracks had at least one edge at a triple point. For each test, the grain-boundary and transcrystalline crack lengths tended to have a log-normal distribution. The logarithmic mean crack length (LMCL) decreased with increasing strain rate, decreasing grain-size and decreasing temperature and tended to a constant value of 0.75 mm at 10°C. For grain-size of 3 mm or greater, the LMCL had a maximum at a strain rate of 10−5 to 10−6 S−1 at −10°C. The LMCLs and the relative proportion of grain-boundary cracks tended to be normally distributed for given load conditions.

Quartz, feldspar and chlorite, the principal minerals in a basal till from the Halasi River catchment in the Altay Mountains, northwestern China, are present in approximately equal concentrations in the coarse fraction of the till, 1.0-0.125 mm. Quartz concentrations are significantly higher than those of the other two minerals in the 0.125-0.016 mm size range. Feldspar and chlorite concentrations are higher than those of quartz in the finest fraction. Quartz has a strong preferred mode at 0.063-0.032 mm. Feldspar and chlorite have two weak modes in the silt-size range, one between 0.063 and 0.032 mm and the other between 0.016 and 0.004 mm.

Thin sections of oriented impregnated samples were used to study crushing and abrasion. Over 2700 daughter particles were identified as products of comminution of 925 parent grains. Quartz and feldspar are most likely to be broken into two particles of roughly equal size, as are fine chlorite grains. However, owing to their weakness and cleavage, larger grains of chlorite tend to he split into more than two daughter particles.

Sizes of the daughter grains were measured and sizes of the original parent grains were estimated. Mean parent grain-sizes for quartz, feldspar and chlorite are 0.129, 0.078 and 0.059 mm, respectively, whereas mean daughter grain-sizes are 0.068,0.041 and 0.024 mm, respectively. The greater percentage reduction in the size of chlorite reflects its tendency to break into more than two daughter particles.

Most grains tend to be crushed. Only a few large particles seem to have suffered from abrasion.

A degree-day glacier mass-balance model is coupled to a dynamic glacier model for temperate glaciers. The model is calibrated for two outlet glaciers from the Hofsjökull ice cap in central Iceland. It is forced with a climate scenario that has recently been defined for the Nordic countries for the purpose of outlining the hydrological consequences of future greenhouse warming. The scenario for Iceland specifies a warming rate of 0.25°C per decade in mid-summer and 0.35°C per decade in mid-winter with a sinusoidal variation through the year. The volume of the glaciers is predicted to decrease by approximately 40% over the next century, and the glaciers essentially disappear during the next 200 years. Runoff from the area that is presently covered by the glaciers is predicted to increase by approximately 0.5 m a−1 30 years from now due to the reduction in the volume of the glaciers. The runoff increase reaches a flat maximum of 1.5–2.0 m a−1 100–150 years from now and levels off after that. The predicted runoff increase leads to a significant increase in the discharge of rivers fed by meltwater from the outlet glaciers of the ice cap and may have important consequences for the operation and planning of hydroelectric power plants in Iceland.

The surface energy budget was investigated during a cruise through the pack ice in the Southern Ocean. The time of observation was close to mid-summer. Some of the more important findings were:

The evolution of four dynamic radar glacier zones at the surface of an alpine icefield in British Columbia is monitored using a time series of 35 First European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images acquired from 1992 to 1994. These zones result from changing wetness and textural properties, and appear to represent: (1) cold snow with no liquid water present; (2) an initial melt front with an upper boundary near the elevation of the 0° isotherm; (3) metamorphosed, rapidly melting first-year snow with a rough or pitted surface; and (4) bare ice. This interpretation is aided by temperature and runoff data, air photographs and field measurements of snowpack properties acquired with two ERS-1 SAR scenes, ice-surface elevations derived from 1:50 000 topographic maps and simulations of radar backscatter from a geometric optics model of surface scattering. Meltwater production is affected by the development of zones (2), (3) and (4), which form, migrate up-elevation and disappear each year between April and September.