Taku Glacier is one of the few glaciers in Alaska, U.S.A., that has advanced over the last century: 7 km since 1890. This advance slowed substantially during the past decade, but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d−1. The advance produced dramatic proglacial sediment deformation up to 200 m in front of the terminus. Two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus. The bulge nearest the terminus was 10 m high and 65 m wide. The middle bulge (7 m high) advanced at 15 cm d−1 and the distal bulge (3 m high and 50 m wide) at 9 cm d−1. Crenulations and prominent fractures developed in the overlying vegetation layer. The frontal lobes of the bulges were steep and overlaid a shear zone, where sediments were being thrust up and over the ground surface. Ice-proximal push moraines, 1–10 m high, formed along much of the 9 km wide terminus, although deformation was minimal at some locations.

A major surge of the glacier complex of Sortebræ, East Greenland, occurred between 1992 and 1995. The impact of this surge on the topography of Sortebræ was examined through the production of a pre-surge (1981) digital elevation model (DEM) from interpolated digital map data, and a post-surge DEM from differential synthetic aperture radar interferometry using European Remote-sensing Satellite (ERS) imagery. The combined vertical error is typically 30–40 m; however, downdraw of up to 270 m in the reservoir zone, and uplift of up to 145 m in the receiving zone were measured. The upper glacier reservoir area discharged in excess of 24.3 ± 9.5 km3 volume over the surge, of which ∼12.5 km3 was stored in the advanced lower glacier, the balance being lost, predominantly to calving.

The inverse barometer effect (IBE) is the isostatic response of ocean surface height to changes in atmospheric pressure (P air) at a rate of about 1 cm hPa−1. The IBE is a significant contributor to variability of ice-shelf surface elevation (η ice), as we demonstrate with simultaneous global positioning system measurements of η ice and local measurements of P air from the Amery, Brunt and Ross Ice Shelves, Antarctica. We find that an IBE correction is justified for frequencies (ω) covering the “weather band”, 0.03 < ω < 0.5 cpd (cycles per day). The IBE correction reduces the standard deviation of the weather-band signal of η ice from ∼9 cm to ∼3 cm. With this correction, the largest remaining high-frequency error signal in η ice is the inaccuracy of the present generation of Antarctic tide models, estimated to be of order 10 cm for most of Antarctica.

Non-steady-state vertical velocities of up to 5 m a−1 exceed the vertical surface-parallel flow (SPF) components over much of the ablation area of Storstrømmen, a large outlet glacier from the East Greenland ice sheet. Neglecting a contribution to the vertical velocity of this magnitude results in substantial errors (up to 20%) also on the south–north component of horizontal velocities derived by satellite synthetic aperture radar interferometry (InSAR) measurements. In many glacier environments, the steady-state vertical velocity component required to balance the annual ablation rate is 5–10 m a−1 or more. This indicates that the SPF assumption may be problematic also for glaciers in steady state. Here we derive the three-dimensional surface velocity distribution of Storstrømmen by using the principle of mass conservation (MC) to combine InSAR measurements from ascending and descending satellite tracks with airborne ice-sounding radar measurement of ice thickness. The results are compared to InSAR velocities previously derived by using the SPF assumption, and to velocities obtained by in situ global positioning system (GPS) measurements. The velocities derived by using the MC principle are in better agreement with the GPS velocities than the previously calculated velocities derived with the SPF assumption.

Extensive albedo data from Storglaciären, Sweden, during nine summers are analyzed, focusing on the effect of surface slope on measurements and on the influence of clouds on albedo of both snow and ice surfaces. On clear-sky days, albedo continuously dropped throughout the day by > 0.3 when derived from measurements in a horizontal plane over the slightly sloping surface. When we correct for the tilt effect, over frozen surfaces the apparent decrease in albedo largely disappeared, while over melting surfaces it became significantly less pronounced. This emphasizes the need to correct horizontally measured data for slope when they are used, for example, as ground truth for satellite-derived albedo, or in high-resolution glacier melt runoff models. Albedo varied by > 0.1 due to cloud fluctuations. To quantify cloud effects, albedo changes between successive (half-)hourly and daily data were regressed against corresponding changes in cloudiness expressed by the ratio of global radiation to top-of-atmosphere solar radiation. The resulting relationship over snow explains 66% of oberved albedo changes using hourly, and 42% using daily, time-steps. Over ice, the corresponding values are 28% and 0%. Hence, cloudiness is a dominating factor in determining short-term variability of albedo over snow, whereas over ice the observed large day-to-day variability ( > 20%) is mainly attributed to changes in the physical characteristics of the weathering crust. Results suggest that cloud effects should be incorporated into models treating snow and ice surfaces separately.

We present a method for analyzing the errors involved in measuring three-dimensional glacier velocities with interferometric radar. We address the surface-parallel flow assumption and an augmented approach with a flux-divergence (FD) term. The errors in an interferometric ERS-1/-2 satellite radar dataset with ascending- and descending-orbit data covering Storstrømmen glacier, northeast Greenland, are assessed. The FD error assessment is carried out on airborne 60 MHz ice-sounding radar data from the same area. A simple model of an interferometric radar system is developed and analyzed. The error sources considered include phase noise, atmospheric distortions, baseline calibration errors, a dry snow layer, and the stationary-flow assumption used in differential interferometry. The additional error sources in the analysis of FD errors are noise, bias and unknown variations of the ice thickness, and approximations of the ice-flow model. The example glacier is now building up following a surge. The analysis shows that in the case study presented the errors are small enough to justify the use of both the estimated surface-parallel flow term of the vertical velocity and the estimated FD term of the vertical velocity.

As a complement to earlier measurements on the friction of both granular fresh-water ice and S2 columnar salt-water ice, new experiments were performed on the friction of S2 columnar fresh-water ice sliding against itself at low velocities (5 × 10−7 to 5 × 10−1 m s−1) and at −10°C, using the same double-shear device as was used earlier. The results showed that under a given set of experimental conditions the kinetic coefficient of friction of S2 fresh-water ice compares favorably with that of the other two variants.The experiments also revealed friction-induced surface cracks and recrystallized grains.These deformation features are explained, respectively, in terms of fracture mechanics and an earlier model of dynamic recrystallization in ice.

A two-dimensional ice-flow model based on the shallow-ice approximation (SIA) is used to investigate the dynamics of Glacier de Saint-Sorlin, France. This glacier is well suited for this kind of study. First, the particular geometry of the glacier itself as well as that of the bedrock surface allows for correct applicability of the SIA (zeroth-order equations), provided that thickness changes and termini positions rather than short-scale dynamics are considered. Secondly, the wealth of available data for the glacier including mass-balance series and records of glacier changes provides a reliable forcing and a powerful constraining set for the model. Steady-state simulations show realistic results and the capabilities of the model in reproducing the glacier extent at the beginning of the 20th century. An extensive parameter study of ice rheology and sliding intensity is also carried out and the results are checked against the thickness changes as well as the glacier termini positions since 1905. It is possible to find a parameter combination that best matches these two types of data with an ice-flow rate factor of 2 × 10−24 Pa−3 s−1 and a Weertman-type sliding factor of 5 × 10−14 m8 N−3 a−1 which both appear to be in agreement with similar inferences from recent modelling attempts.

Repeat airborne laser altimeter measurements are used to derive surface elevation changes on parts of Whillans Ice Stream and Ice Stream C, West Antarctica. Elevation changes are converted to estimates of ice equivalent thickness change using local accumulation rates, surface snow densities and vertical bedrock motions. The surveyed portions of two major tributaries of Whillans Ice Stream are found to be thinning almost uniformly at an average rate of ∼1 m a−1. Ice Stream C has a complicated elevation-change pattern, but is generally thickening. These results are used to estimate the contribution of each surveyed region to the current rate of global sea-level rise.

Quantitative ice-core paleoclimatology must account for post-depositional processes, such as vapor-phase diffusion in the firn. After pore close-off, diffusion continues to smooth the stable-isotope records δ18O and δD that are eventually recovered from the ice, leading to the loss of high-frequency information. Johnsen and others (1997) found much higher rates of diffusive smoothing in the Greenland Icecore Project (GRIP) Holocene ice than would be predicted by diffusion through solid ice alone, and Nye (1998) argued that transport through liquid veins might explain this apparent excess diffusion. However, the analysis of Johnsen and others (2000) indicates that the required vein dimensions may be unrealistically large. Here, we model the diffusion of stable isotopes in polycrystalline ice and show that the predictions of Nye (1998) and those of Johnsen and others (2000) actually represent two end-members in a range of potential behavior. Our model determines which of these asymptotic regimes more closely resembles the prevailing conditions and quantifies the role of pre-melted liquid in the smoothing of isotopic signals. The procedure thereby ties together the two approaches and provides a rostrum for accurate analysis of isotope records and paleotemperature reconstructions.

Glaciers are an important element of the environment in the source regions of the Yangtze and Yellow rivers on the Tibetan Plateau. Using Geographical Information System techniques, we have studied changes in the location of glacier margins in two areas: the Geladandong area in the headwaters of the Yangtze, and the A’nyêmaqên Shan mountains in the headwaters of the Yellow River. Marginal positions during the Little Ice Age (LIA) maximum, in 1969 in the Geladandong area, in 1966 in the A’nyêmaqên Shan, and in 2000 in both areas, were determined using aerial photographs, satellite images, topographical maps and digital elevation models. Extrapolating the results to the entire source regions of the Yangtze and Yellow rivers, we estimate that the total glacierized area decreased about 1.7% between 1969 and 2000 in the Geladandong area and about 17% between 1966 and 2000 in the A’nyêmaqên Shan. Glaciers were stable or advanced slightly between 1969 and 1995 in the Geladandong area, and between 1966 and 1981 in the A’nyêmaqên Shan, but have retreated since the mid-1990s in the former and since the 1980s in the latter. Significant increases in summer air temperature and decreases in annual precipitation are the causes of the present retreat. As a consequence of the retreat, water storage, as ice, in the Yangtze and Yellow river drainages is decreasing by 65–70 × 106 m3 a−1.

The genesis of some types of patterned ground, including hummocks, frost boils and sorted stone circles, has been attributed to differential frost heave (DFH). However, a theoretical model that adequately describes DFH has yet to be developed and validated. In this paper, we present a mathematical model for the initiation of DFH, and discuss how variations in physical (i.e. soil/vegetation properties) and environmental (i.e. ground/air temperatures) properties affect its occurrence and length scale. Using the Fowler and Krantz multidimensional frost-heave equations, a linear stability analysis anda quasi-steady-state real-time analysis are performed. Results indicate that the following conditions positively affect the spontaneous initiation of DFH: silty soil, small Young’s modulus, small non-uniform surface heat transfer or cold uniform surface temperatures, and small freezing depths. The initiating mechanism for DFH is multidimensional heat transfer within the freezing soil. Numerical integration of the linear growth rates indicates that expression of surface patterns can become evident on the 10–100 year time-scale.

Jakobshavn Isbræ is the most active glacier in Greenland, with an annual discharge of about 30 km3 of ice, and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998, despite locally warm summers. Repeated airborne laser-altimeter surveys along a 120 km profile in the glacier basin show slow, sporadic thickening between 1991 and 1997, suggesting a small positive mass balance, but since 1997 there has been sustained thinning of several m a−1 within 20 km of the ice front, with lower rates of thinning further inland. Here, we use weather-station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates, and thus to infer the temporal and spatial patterns of dynamic thinning. These show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning, initially confined to the lower reaches of the glacier (below about 500 m elevation), but progressively spreading inland until, between 1999 and 2001, thinning predominated over the entire surveyed region, up to 2000 m elevation. If this continues, the glacier calving front and probably its grounding line will retreat substantially in the very near future.

A deformation-controlled triaxial apparatus has been developed in order to investigate the mechanical behaviour of alpine snow. Cylindrical specimens (58 mm in diameter, 126 mm in height) can be axially deformed by applying tensile or compressive strain rates between 2.4 × 10−7 s−1 and 2.4 × 10−2 s−1. Compressed air is used to laterally load the snow specimens with pressures of up to 40 k Pa.The volumetric deformation is found by carefully encapsulating the snow samples in an airtight Mylar foil and measuring the expelled pore air during sample deformation. The multidimensional stress–strain behaviour can therefore be determined, and constitutive theories of snow advanced. The device is located in the cold rooms of the Weissfluhjoch research station of the Swiss Federal Institute for Snow and Avalanche Research. Some 180 tests have been performed over the last four winters. The density of the snow specimens varied between 190 and 435 kg m−3. Part I of this two-part paper discusses the development of the apparatus and the applied testing methodology. Qualitative results are provided. In Part II, a detailed analysis of the results is presented and the viscoelastic properties of snow quantified.

The longitudinal pattern of surface velocity of a large, predominantly cold, polythermal glacier (John Evans Glacier, Ellesmere Island, Canada) was measured over summer and winter periods. In the accumulation and upper ablation areas, where ice is predominantly cold-based, summer velocities were slightly higher than overwinter velocities. Predicted velocities due to ice deformation alone in these areas closely matched these observations in the winter, with limited basal motion likely in the summer. In the lower ablation area, where ice is likely warm-based, measured summer velocities were up to double overwinter velocities. Predicted ice deformation could not account for all of these measured velocities in either summer or winter. This suggests that basal motion occurs throughout the year over at least part of the lower ablation area. This finding is supported by radio-echo sounding, subglacial drainage reconstructions and analyses of early-summer meltwater chemistry, which suggest that subglacial water is present throughout the year in this region. In summer, basal motion may account for up to 75% of the total surface velocity throughout the lower ablation area. The inferred rate of basal motion increases sharply directly below a set of moulins by which most surface meltwater reaches the glacier bed.

Catchment-wide information on glacier snow-cover depth, surface albedo and surface roughness is important input data for distributed models of glacier energy balance. In this study, we investigate the small-scale (mm to 100 m) spatial variability in these properties, with a view to better simulating this variability in such models. Data were collected on midre Lovénbreen, a 6 km2 valley glacier in northwest Svalbard. The spatial variability of all three properties was found to be self-similar over the range of scales under investigation. Snow depth and albedo exhibit a correlation length within which measurements were spatially autocorrelated. Late-winter and summer properties of snow depth differed, with smaller depths in summer due to melt, and shorter correlation lengths. Similar correlation lengths for snow depth and surface albedo may suggest that snow-depth variation is an important control on the small-scale spatial variability of glacier surface albedo. For surface roughness, the data highlight a possible problem in energy-balance studies which use microtopographic surveys to calculate aerodynamic roughness, in that the scale of the measurements made affects the calculated roughness value. This suggests that further investigations of the relationships between surface form and aerodynamic roughness of glacier surfaces are needed.

Three early-melt-season high-velocity events (or “spring events”) occurred on Haut Glacier d’Arolla, Switzerland, during the melt seasons of 1998 and 1999. The events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures. However, differences in spatial patterns of surface velocity, internal ice deformation rates, the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls. The data from two of the events suggest widespread ice–bed decoupling, particularly along a subglacial drainage axis creating the highest rates of basal motion and “plug flow” in the overlying ice. The other event showed evidence of less extensive ice–bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas. We suggest that: (1) plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag; (2) under certain circumstances, enhanced surface motion may be due in part to non-locally forced enhanced bed deformation; and (3) subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres.

Fine-grained, dry snow with a density range of 190–435 kg m−3 was tested in triaxial compression at −12°C with confining pressures varying between 0 and 40 kPa. The tests were strain-rate controlled, with strain rates ranging between 7.4 × 10−7 s−1 and 6.6 × 10−5 s−1. The analysis of the test results revealed that the relationship between yield stress and viscous strain rate is best given by a power law, similar to polycrystalline ice. However, the power-law exponent n is a function of density and varies between 1.8 (low-density snow, ρ < 200 kg m−3) and 3.6 (high-density snow, ρ > 320 kg m−3). The tests also showed that lower-density snow displays a significant non-linear stress–strain response before yielding. Two further aspects of the constitutive behaviour of snow were identified: (1) the strainrate independence of the post-yield work-hardening behaviour in compression and (2) the independence of the axial yield stress in relation to the confining pressure. The experimental observations are discussed with respect to the mechanical properties of polycrystalline ice, which is the constituent material of the load-bearing ice skeleton.

We present some new results describing energy exchange processes of drifting sea ice in the marginal ice zone (MIZ) in the Barents Sea, Arctic Ocean. All measurements and observations of meteorological parameters and ice conditions were taken on board the Norwegian research vessel Lance from 3 to 22 May 1999. Components of surface heat balance were measured and correlated with ice conditions and synoptic observations. These results can be used in atmospheric boundary layer modelling as lower boundary conditions. A relationship was found between modelled turbulent heat fluxes and observed sea-ice concentrations.

Mega-scale glacial lineations (MSGLs) are longitudinally aligned corrugations (ridge–groove structures 6–100 km long) in sediment produced subglacially. They are indicators of fast flow and a common signature of ice-stream beds. We develop a qualitative theory that accounts for their formation, and use numerical modelling, and observations of ice-stream beds to provide supporting evidence. Ice in contact with a rough (scale of 10–103 m) bedrock surface will mimic the form of the bed. Because of flow acceleration and convergence in ice-stream onset zones, the ice-base roughness elements experience transverse strain, transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards. Where such keels slide across a soft sedimentary bed, they plough through the sediments, carving elongate grooves, and deforming material up into intervening ridges. This explains MSGLs and has important implications for ice-stream mechanics. Groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream. Keels may provide basal drag in the force budget of ice streams, thereby playing a role in flow regulation and stability. We speculate that groove ploughing permits significant ice-stream widening, thus facilitating high-magnitude ice discharge.