Tidewater glaciers deposit sediment at their terminus, thereby reducing the relative water depth. Reduced water depth can lead to increased glacier stability through decreased rates of iceberg calving, glacier thinning and submarine melting. Here we investigate sedimentation processes at the termini of Kronebreen and Kongsvegen, Svalbard. We mapped the fjord floor bathymetry in August 2009 and calculate sedimentation rates based on our bathymetry and that from a similar study in 2005. A grounding-line fan is developing near the current position of the subglacial stream. An older, abandoned grounding-line fan that likely formed between ∼1987 and 2001 is degrading near the middle of the ice front. Our findings indicate that sediment gravity flows reduce the height of the sediment mound forming at the glacier terminus. The future impact of glacimarine sedimentation processes on glacier stability will depend on the net balance between the observed gravity flows and sediment deposition.

Analyses of shallow cores obtained at the European Project for Ice Coring in Antarctica (EPICA) drilling site Kohnen station (75°00′ S, 00°04′ E; 2892 m a.s.l.) on the plateau of Dronning Maud Land reveal the presence of conserved snow dunes in the firn. In situ observations during three dune formation events in the 2005/06 austral summer at Kohnen station show that these periods were characterized by a phase of 2 or 3 days with snowdrift prior to dune formation which only occurred during high wind speeds of >10 m s-1 at 2 m height caused by the influence of a low-pressure system. The dune surface coverage after a formation event varied between 5% and 15%, with a typical dune size of (4 ± 2) m × (8 ± 3) m, a maximum height of 0.2 ± 0.1 m and a periodicity length of about 30 m. The mean density within a snow dune varied between 380 and 500 kg m-3, whereas the mean density at the surrounding surface was 330 ± 5 kgm-3. The firn cores covering a time-span of 22 ± 2 years reveal that approximately three to eight events per year occurred, during which snow dunes had been formed and were preserved in the firn.

A mechanical model with circular symmetry is examined to test the hypothesis that the Martian ice caps are composed of flowing water ice, together with some rock debris. In contrast with most or all previous models, no assumption of a steady state is made. Instead the accumulation and ablation is assumed to be insignificant, and it is suggested that after a sufficient time the profile would have settled down to a particular collapsing form calculated by Halfar (1983). Higher modes of flow would have decayed relatively quickly. To calculate the time constant, it is necessary to consider carefully the distribution of temperature with depth. The time constant is sensitive to the grain-size, which is assumed to be 1–10 mm and is a significant unknown, as is also the effect of preferred crystal orientation. Apart from this, the main uncertainty is the value of the upward heat flux. With a heat flux of 30 mW m−2, the water-ice hypothesis is consistent with an age of about 107 years for both the north and the south polar caps, the north cap being the younger by a factor of about 7.

Investigating snow avalanches using a purely statistical approach raises several issues. First, even in the heavily populated areas of the Alps, there are few data on avalanche motion or extension. Second, most of the field data are related to the point of furthest reach in the avalanche path (run-out distance or altitude). As data of this kind are tightly dependent on the avalanche path profile, it is a priori not permissible to extrapolate the cumulative distribution function fitted to these data without severe restrictions or further assumptions. Using deterministic models is also problematic, as these are not really physically based models. For instance, they do not include all the phenomena occurring in the avalanche movement, and the rheological behaviour of the snow is not known. Consequently, it is not easy to predetermine extreme-event extensions. Here, in order to overcome this problem, we propose to use a conceptual approach. First, using an avalanche-dynamics numerical model, we fitted the model parameters (friction coefficients and the volume of snow involved in the avalanches) to the field data. Then, using these parameters as random variables, we adjusted appropriate statistical distributions. The last steps involved simulating a large number of (fictitious) avalanches using the Monte Carlo approach. Thus, the cumulative distribution function of the run-out distance can be computed over a much broader range than was initially possible with the historical data. In this paper, we develop the proposed method through a complete case study, comparing two different models.

A dark region in the western ablation zone of the Greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice. These higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone. To deduce the period and the causes of this higher dust deposition, carbonaceous particles in ice samples from the dark region and from brighter reference ice were analysed and used for dating. Samples including ice from directly below the surface contain high amounts of modern organic carbon, probably from microorganisms on the ice surface. Deeper samples reveal low amounts of carbonaceous particles, which are originally deposited in the accumulation zone. The amount of outcropping carbonaceous particles in the dark region seems significantly higher than in the reference ice. One of the samples that contained material initially deposited in the accumulation zone was dated and revealed Late Holocene ages, coinciding with a period of enhanced eolian activity in the nearby tundra. Therefore, variable eolian activity during the Holocene effected dust fluxes towards the ice and hence leads to albedo variations in the present ablation zone of the ice sheet.

Sintering rates in snow were investigated by measuring changes in penetration resistance with time and by using a numerical snow metamorphism model. Periodic Snow Micro Penetrometer (SMP) measurements were performed on uniform snow samples covering a wide range of densities. The mean penetration resistance of snow increased with time according to a power law with an average exponent of 0.18. Simulated changes in the bond-to-grain ratio for simplified spherical ice grains followed a power law with an average exponent of 0.18, showing that the mean penetration resistance, as measured with the SMP, closely relates to bond-to-grain ratio in snow. For lower-density snow samples, consisting mostly of dendritic snow morphologies, the measured increase in penetration resistance was lower. This is likely the result of two competing processes: (1) strengthening of the snow sample due to the creation and growth of bonds and (2) weakening of the snow sample due to the formation of unbonded small rounded particles at the expense of larger dendritic forms. On the other hand, the rate of increase in penetration resistance for snow samples consisting of closely packed depth hoar was similar to that of rounded grains.

This paper presents the impact of model resolution on the simulated wind speed, drifting snow climate and surface mass balance (SMB) of Terre Adélie and its surroundings, East Antarctica. We compare regional climate model simulations at 27 and 5.5 km resolution for the year 2009. The wind speed maxima in Terre Adélie and the narrow glacial valleys of Victoria Land are better represented at 5.5 km resolution, because the topography is better resolved. Drifting snow sublimation is >100 mm a-1 in regions with high wind speeds. Our results indicate a strong feedback between topography, wind gradients and drifting snow erosion. As a result, SMB shows much more local spatial variability at 5.5 km resolution that is controlled by drifting snow erosion, whereas the large-scale SMB gradient is largely determined by precipitation. Drifting snow processes lead to ablation in the narrow glacial valleys of Victoria Land. The integrated SMB equals 86 Gt. Although wind climate, drifting snow processes and SMB variability are better represented at 5.5 km, the area-integrated SMB is not significantly different between the simulations at 27 and 5.5 km. A horizontal resolution of 27 km is sufficient to realistically simulate ice-sheet wide SMB.

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.

High-resolution surface velocity measurements and passive seismic observations from Rutford Ice Stream, West Antarctica, 40 km upstream from the grounding line are presented. These measurements indicate a complex relationship between the ocean tides and currents, basal conditions and ice-stream flow. Both the mean basal seismicity and the velocity of the ice stream are modulated by the tides. Seismic activity increases twice during each semi-diurnal tidal cycle. The tidal analysis shows the largest velocity variation is at the fortnightly period, with smaller variations superimposed at diurnal and semi-diurnal frequencies. The general pattern of the observed velocity is two velocity peaks during each semi-diurnal tidal cycle, but sometimes three peaks are observed. This pattern of two or three peaks is more regular during spring tides, when the largest-amplitude velocity variations are observed, than during neap tides. This is the first time that velocity and level of seismicity are shown to correlate and respond to tidal forcing as far as 40 km upstream from the grounding line of a large ice stream.

Glaciological ablation is computed from point-scale data at a few ablation stakes that are usually regressed as a function of elevation and averaged over the area-elevation distribution of a glacier. This method is contingent on a tight control of elevation on local ablation. However, in debris-covered glaciers, systematic and random spatial variations of debris thickness modify the ablation rates. We propose and test a method to compute sub-debris ablation where stake data are interpolated as a function of debris-thickness alone and averaged over the debris-thickness distribution at different parts of the glacier. We apply this method on Satopanth Glacier located in Central Himalaya utilising ~1000 ablation measurements obtained from a network of up to 56 stakes during 2015–2017. The estimated mean sub-debris ablation ranges between 1.5±0.2 to 1.7±0.3 cm d−1. We show that the debris-thickness-dependent regression describes the spatial variability of the sub-debris ablation better than the elevation dependent regression. The uncertainties in ablation estimates due to the corresponding uncertainties in the measurement of ablation and debris-thickness distribution, and those due to interpolation procedures are estimated using Monte Carlo methods. Possible biases due to a finite number of stakes used are also investigated.

Two small glaciers on James Ross Island, the north-eastern Antarctic Peninsula, experienced surface mass gain between 2009 and 2015 as revealed by field measurements. A positive cumulative surface mass balance of 0.57 ± 0.67 and 0.11 ± 0.37 m w.e. was observed during the 2009–2015 period on Whisky Glacier and Davies Dome, respectively. The results indicate a change from surface mass loss that prevailed in the region during the first decade of the 21st century to predominantly positive surface mass balance after 2009/10. The spatial pattern of annual surface mass-balance distribution implies snow redistribution by wind on both glaciers. The mean equilibrium line altitudes for Whisky Glacier (311 ± 16 m a.s.l.) and Davies Dome (393 ± 18 m a.s.l.) are in accordance with the regional data indicating 200–300 m higher equilibrium line on James Ross and Vega Islands compared with the South Shetland Islands. The mean accumulation-area ratio of 0.68 ± 0.09 and 0.44 ± 0.09 determined for Whisky Glacier and Davies Dome, respectively, is similar to the value reported for Vega Island and within the range of typical values for high-latitude glaciers.

More than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice. The results proved to be extremely sensitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness lengths were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.

A simple flux model using twice-daily measurements of wind, humidity and temperature from standard upper-air levels in a distant radiosonde estimated winter balance of South Cascade Glacier, Washington, U.S.A., over 1959–98 with error 0.24 m w.e. Correlation between net and winter balance is strong; the model estimates net balance with error 0.53 m w.e. Over the past 40 years, average net balance of South Cascade Glacier has been strongly negative (−0.46 m w.e.), and it has been shrinking steadily. In comparison, 200 km west-southwest at Blue Glacier, the average balance has been less negative (−0.13 m w.e); that glacier has undergone little change over the 40 years. Balance histories of the two glaciers are positively correlated (r = +0.54), and South Cascade has been more out of balance than Blue, presumably because it is still adjusting to climate change since the Little Ice Age. Recent warming and drying has made the net balance of both glaciers strongly negative since 1976 (−0.84 m w.e. at South Cascade, −0.56 m w.e. at Blue). If South Cascade Glacier were in balance with the 1986–98 climate, it would be about one-quarter of its present area.

Ice shelves and ice tongues are dynamically coupled to their cavities. Here we compute normal modes (eigenfrequencies and eigenfunctions) of this coupled system using a thin-plate approximation for the ice shelf and potential water flow in the ice-shelf cavity. Our results show that normal modes depend not only on the ice-shelf parameters (length, thickness, Young’s modulus, etc.) but also on the cavity depth. The dominant eigenmodes are higher for ice shelves floating over deeper cavities; they are also higher for shorter ice shelves and ice tongues (<50 km long). The higheigenfrequency eigenmodes are primarily controlled by the ice flexure and have similar periods to sea swell. These results suggest that both long ocean waves with periods of 100–400 s and shorter sea swell with periods of 10–20 s can have strong impacts on relatively short ice shelves and ice tongues by exciting oscillations with their eigenfrequencies, which can lead to iceberg calving and, in some circumstances, ice-shelf disintegration.

Interferometric radar images collected by ERS-1, ERS-2 and RADAR- SAT-1 are used to observe the rupture tip of rifts that propagate along Hemmen Ice Rise on the Ronne Ice Shelf, Antarctica. Interferograms generated in 1992 and 1997 allow for the observation of ice deformation accumulated over 9 and 24 days respectively. These interferograms are combined, in order to separate the continuous process of creep deformation from the more cyclic motion caused by variations in ocean tide. An examination of local gradients in creep deformation reveals the pattern of ice deformation around and near the rupture tips and rifts with great precision (up to 10 cm a-1). We compare the observations with a deformation model for ice and obtain the following results: (1) The tidal oscillation of the Ronne Ice Shelf only yields small deformations along the rifts and near the rupture tips. (2) Along the ice front, the rifts and at the rupture tips, vertical bending is observed which is well explained by a model of viscous deformation of ice. Furthermore, the model indicates that the deformation pattern observed at the rupture tips is a sensitive indicator of the propagation state of the rifts (i.e. active vs inactive). (3) The viscous adjustment of ice is the dominant mode of deformation, masking the deformation pattern predicted by linear elastic fracture mechanics (LEFM). (4) Yet, at a spatial scale equivalent to the length of a rift, the propagation rate is well predicted by LEFM.

Glaciers and the periglacial environment in Argentina have been protected by the Law since 2010. This legislation required the development of the first National Glacier Inventory (NGI), which was officially presented in May 2018 and based on satellite images spanning between 2004 and 2016. Here, we present the methods and results of the NGI, summarize the glaciers’ morphological and spatial characteristics, and compare our results to previous regional and global inventories. The NGI reveals an impressive variety of ice masses including rock glaciers, permanent snowfields, mountain and valley glaciers with varying amounts of debris-cover and large outlet glaciers. The Argentinean Andes contain 16 078 ice masses covering an area of 5769 km2 between 200 and 6900 m a.s.l. Comparison of the combined national inventories of Argentina and Chile (~30 000 glaciers and 28 400 km2) with the Randolph Glacier Inventory 6.0 for the Southern Andes (~16 000 glaciers and 29 400 km2), shows that there are large differences in extent and number of glaciers in some sub-regions. The NGI represents an improvement for a better understanding of Argentina's freshwater reservoirs and provides detailed information for the preservation and study of ice masses along 4000 km of the Southern Andes.

Helicopter-borne 135 MHz short-pulse radar profiles of the Bagley Ice Field, southern Alaska, U.S.A., have been analyzed to determine the nature of radio-wave propagation through crevassed, stratified, wet and draining firn. Diffractions characterize the firn horizons along the trunk, and reflections characterize those of overlying snow-fields. Dynamic stacking was used to form and determine firn depths, and unstacked diffraction analysis to determine firn-layer properties. Refractive indices range from 4.1 to 4.5 for the near-surface, from 1.7 to 2.1 at about 13–17 m depth along the main trunk, and to 2.6 to 58 m depth within a snowfield. Average trunk values correspond with volumetric water contents of about 0.09, which agree with values measured for other glaciers. The analysis of the airborne-recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake-bottom diffraction. The lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions. The reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect, and they predict low interlayer transmission losses. The snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design.

A survey of July 1st glacier, Qilian Shan, China, was carried out in 2002. Previously, the glacier’s boundary had been recorded in 1956, and further research had been carried out in the mid- 1970s and 1980s. Our survey reveals that area shrinkage and surface lowering have accelerated in the past 15 years. Surface elevation changes can result from changes in accumulation, surface melting and emergence velocity. The contributions of these elements to surface lowering are evaluated at the lower part of the glacier from observations of surface velocity, ice thickness and precipitation, and from temperature data near the glacier. Apart from the effect of glacier ice redistribution, our analysis reveals quantitatively that the recent accelerated glacier shrinkage has been caused by increasing temperature. Furthermore, it is established that meltwater discharge from the glacier in the past 17 years has increased due to glacier shrinkage, by about 50% over that from 1975 to 1985.

Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semiautomatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of ~1300 glaciers were misclassified. The algorithm was validated on >25 000 km2 of ice in other regions in Alaska and on >40 000 km2 of ice in Arctic Canada, resulting in ~2% and ~3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.