Deep gravel-pit exposures reveal the distribution and structure of till and underlying sand and gravel in drumlins near Waukesha, Wisconsin. The subglacial sediment is interpreted to have moved laterally into the drumlin sites because the till thickens from the margin to the core of the drumlins, the stone orientation in the till is perpendicular and oblique to ice flow on the drumlin margins, and recumbent isoclinal folds occur in sand on the drumlin margins with axes parallel to the drumlin axes. The resulting accumulations of sediment presented obstacles to ice flow and were streamlined into the minimum-drag drumlin shape by erosion on the margins and by remolding of material in the core of the drumlins. These drumlin nuclei may have formed at spots where there was low effective stress on the bed. The subglacial sediment became mobile as a result of high pore pressure that may have developed as ground water and subglacial melt water were trapped behind a frozen bed at the ice margin. Under certain conditions, however, lateral sediment flow might also have occurred when the sediment was frozen.

A theoretical basis for introducing capillary effects into the theory of water percolation through snow is given. A capillary pressure-liquid saturation relationship found in the laboratory is used together with the theory to make a quantitative examination of capillary effects. It is shown that capillarity accounts for less than 10% of the total force when water flux is 10–8 m s–1 although the percentage rapidly increases for smaller fluxes. The experiments suggest that the irreducible water content of dense snow is 7% of the pore volume. It is concluded that the wave-front diffusion seen in lysimeter studies is not the result of capillary action. Other possible causes are suggested.

Results of pollen analysis of a large firn sample from Dye 3, southern Greenland, are reported. The sample was divided into three sections: all dominated by pine, birch, and ragweed pollen. Pollen concentration for the entire sample is 15 pollen grains per litre and the annual pollen deposition rate has been estimated at approximately 0.73 grains cm−2 year−1 (7300 grains m−2 a−1). Although these values are slightly lower than expected, considering the relatively southern latitude of the site, they are within the range of values obtained from other Arctic ice caps.

Measurements of strain-rates on a temperate glacier in a region of initial transverse fracturing indicate a critical strain-rate of 3.5±0.5 × 10−5 d−1, associated with a regional strain-rate gradient of 5 × 10−8 d−1 m−1. At only one section of the glacier is the theoretical longitudinal strain-rate (Nye, 1959[c]) in approximate agreement with the value measured at the surface at that point. Corresponding measurements on a polar glacier (temperature −27.9°C at 10 m depth during the summer) indicate that the critical strain-rate is about 0.6±0.05 × 10−5 d−1, which is associated with a gradient of strain rate of about 3 × 10−9 d−1 m−1. At one section there is close agreement between the theoretical and measured longitudinal strain-rate. For the temperate glacier crevasse depths ranged from 23.5 to 28 m; in the polar glacier one crevasse was 23.9±0.5 m deep, assuming a wedge form. Only an approximate agreement with the measured values of depth is obtained by using the regional strain-rate values in Nye’s crevasse-depth formula.

Over a distance of 1.2 km the temperate glacier transverse crevasse spacings are very variable, ranging from 30 m to 96 m, but initially the spacings range from 55 m to 96 m, and for the first four cases the spacing s varies from 2.7 d to 3.3 d, where d is the crevasse depth. In the cold ice, crevasse spacings are far more uniform, ranging from 57 m to 66 m. A value of s ≈ 2.5 d is obtained in only one case. This greater uniformity of spacing may be explained in terms of the dynamics of flow. Despite large differences in thermal, dimensional and strain-rate parameters between the two glaciers, (1) the crevasse depths are closely similar, and (2) the spacings of crevasses are similar. It has been demonstrated from two lines of evidence that the assumption that the strain on an intercrevasse block is negligible is not correct. The direction of the principal extending strain-rate is, in the most reliable cases, perpendicular to the crevasse traces within 2° to 7°.

In 1983 three directional surveys were made in the bore hole from which a deep ice core was obtained in the summers of 1979–81. The inclination and azimuth of the bore hole were measured on three surveys, temperature was included on two surveys, fluid pressure and hole diameter on one of the surveys. Fluid-pressure measurements show that the ice-overburden pressure was undercompensated in the upper few hundred meters and overcompensated at the bottom of the hole. Diameter measurements show closure in the upper portion and expansion near the bottom beginning at the transition from the Holocene to Wisconsin ice at 1784 m. The hole expansion and increase in inclination correlate with dust and silt content in the Wisconsin ice. Changes in azimuth are due to flow of the ice and are consistent with the direction of flow at the surface. Temperature measurements show that the hole is at or near equilibrium. The gradient of 0.012 K/m below 1400 m is less than the 0.018 K/m at Camp Century. There is a slight reduction in gradient near the bottom from internal friction in the silty ice.

Spatial heterogeneity of snow and firn properties on glaciers introduces uncertainty in interpretation of point and profile observations and complicates modelling of meltwater percolation and runoff. Here we present a study of the temporal and spatial dynamics of firn density and stratigraphy at the plot-scale (≈10 m × 10 m × 10 m) repeated annually during 2012–14 at the Lomonosovfonna icefield, Svalbard. Results from cores, video inspections in boreholes and radar grid surveys are compared. Ice layers 0.1–50 cm thick comprised ≈8% of the borehole length. Most of them are 1–3 cm thick and could not be traced between boreholes separated by 3 m. Large lateral variability of firn structure affects representativeness of observations in single holes and calls for repeated studies in multiple points to derive a representative stratigraphy signal. Radar reflections are poorly correlated with ice layers in individual boreholes. However, the match between the high amplitude peaks in the grid-averaged radar signal and horizons of preferential ice layer formation revealed by averaging the video surveys over multiple boreholes is higher. These horizons are interpreted as buried firn layers previously exposed to melt-freeze or wind-driven densification and several of them are consistently recovered throughout three field campaigns.

A general survey of the preliminary results of a three-year program of measurements on the Amery Ice Shelf by A.N.A.R.E. are presented, together with theoretical considerations of the velocity and stress distributions and the mass and energy regimes of the ice shelf.

In order to explain the observed velocity distribution it has been found necessary to extend Weertman’s theory of ice-shelf creep to an ice shelf bounded at its sides. The resulting theoretical velocity profile applied to the results of the Amery Ice Shelf provides estimates of the average values of the power flow-law parameters for the ice shelf.

The energy and mass budget considerations, together with the recorded change in form of the ice front, suggest that the ice-shelf regime is not in a continual state of balance but may fluctuate as the ice shelf changes in form over a period of about forty years.

The Tian Shan mountain range, known as the water towers of Central Asia, plays a key role in local water supply, yet large uncertainties remain about the amount of water that is stored in its glaciers. In this study, we assess the impact of the boundary conditions on ice thickness estimates using two inversion models: a mass conservation (MC) model and a basal shear stress (BS) model. We compare the widely used Randolph Glacier Inventory version 6 with the updated Glacier Area Mapping for Discharge from the Asian Mountains glacier inventory, as well as two digital elevation models (SRTM DEM and Copernicus DEM). The results show that the ice volume (in ~2000 CE) in the Tian Shan range is 661.0 ± 163.5 km3 for the MC model and 552.8 ± 85.3 km3 for the BS model. There are strong regional differences due to inventory, especially for glaciers in China (17–25%). However, the effect of different DEM sources on ice volume estimation is limited. By the end of the 21st century, the projected mass loss differences between inventories are higher than between adjacent emission scenarios, illustrating the vital importance of high-quality inventories. These differences should be carefully considered during water resource planning.

Avalanche accidents are increasing in Scotland and fatalities now average two each year. The victims are either mountaineers or cross-country skiers as the problem is confined to the steeper and remoter slopes. Studies in the Cairngorm Mountains have shown that Scottish snow differs from alpine snow in three respects: depth hoar does not occur in Scotland, higher values are found for density and rammsonde penetration, and ice layers are more abundant. Slab avalanches are found on slopes of about 35° and sluffs on slopes of 30° and steeper. Although most avalanches are small, crown fracture lines reach a maximum length of 500 m, and slabs may be up to eight metres thick. Preliminary correlations between avalanche release and weather conditions have shown the importance of cold periods following heavy snow falls and the significance of thaws. Much more needs to be done before an avalanche-forecasting service could be provided, not the least of which is persuading likely beneficiaries that such a service would be worthwhile.

We recorded the burial times of temperature sensors mounted on a specially constructed tower to determine snow accumulation during individual storms in the summit caldera of Mount Wrangell, Alaska, USA, (62° N, 144° W; 4100 m a.s.l.) during the accumulation year June 2005 to June 2006. The experiment showed most of the accumulation occurred in episodic large storms, and half of the total accumulation was delivered in late summer. The timing of individual events correlated well with storms recorded upwind, at Cordova, the closest Pacific coastal weather station (200 km south-southeast), although the magnitude of events showed only poor correlation. Hence, snow accumulation at Mount Wrangell appears to be a reflection of synoptic-scale regional weather systems. The accumulation at Mount Wrangell’s summit (>2.5 m w.e.) exceeded the precipitation at Cordova. Although the direct relationship between accumulation of individual storms at the summit of Mount Wrangell and precipitation events at Cordova may be unique in the region, it is useful for interpreting ice cores obtained on Mount Wrangell. This is especially the case here because the high rate of accumulation allows high time resolution within the core.

A hybrid analytical and random-walk model has been developed to predict the shape of ice accreted on a horizontal cylindrical insulator due to freezing rain. The freezing rain occurs with the temperature of the vertically falling raindrops above the freezing point and the air temperature below freezing. The analytical model calculates the angular distribution of the water-film temperature and the location where freezing begins. The random-walk model predicts the accretion shape. The two random-walk model parameters, the freezing probability and the shedding parameter, are expressed as functions of the atmospheric conditions. The model predicts a variety of realistic accretion shapes from cylindrical to icicle-like. Model verification based on comparisons with other models and with experimental results demonstrates quantitatively and qualitatively the credibility of this new modelling approach.

Melting glacier surfaces are unique ecosystems for specialized microbes, frequently harbouring blooms of microalgae with pigments contributing to the darkening of ice surfaces, reducing albedo and enhancing melt rates. The main cause of this phenomenon is algae of the genus Ancylonema. Prior investigation depended on field-collected material because these algae resisted cultivation. To enhance research on how these algae dominate melting ice, we established a strain of Ancylonema alaskanum from an alpine glacier and exposed to temperatures around the freezing point at irradiations of ~10% of full sunlight. The morphology of the culture changed, with the cells becoming longer and turning green by losing their brownish pigmentation, indicating that these dark phenols are crucial for survival in the cryosphere. Photophysiological comparisons of strain and glacial material showed adaptation of the photosynthetic apparatus to prevailing conditions. This laboratorial strain opens possibilities for a wide range of comparative ‘omics’ research.

I explore the tidewater glacier cycle with a 1-D, depth- and width-integrated flow model that includes a mass-flux calving parameterization. The parameterization is developed from mass continuity arguments and relates the calving rate to the terminus velocity and the terminus balance velocity. The model demonstrates variable sensitivity to climate. From an advanced, stable configuration, a small warming of the climate triggers a rapid retreat that causes large-scale drawdown and is enhanced by positive glacier-dynamic feedbacks. Eventually, the terminus retreats out of deep water and the terminus velocity decreases, resulting in reduced drawdown and the potential for restabilization. Terminus readvance can be initiated by cooling the climate. Terminus advance into deep water is difficult to sustain, however, due to negative feedbacks between glacier dynamics and surface mass balance. Despite uncertainty in the precise form of the parameterization, the model provides a simple explanation of the tidewater glacier cycle and can be used to evaluate the response of tidewater glaciers to climate variability. It also highlights the importance of improving parameterizations of calving rates and of incorporating sediment dynamics into tidewater glacier models.

Five glacial phases are recognized in the area described. Two of these are represented by the deposits of ice-sheets from the north-east and north-west respectively; the other three were of local origin. The materials composing the drifts differ sufficiently to enable the stratigraphy to be seen clearly. This shows that the local ice caps alternated with the invading ice sheets—which brings out a point of considerable climatological interest in that it is clear that the local ice advanced not simultaneously with the invading ice sheets but alternated with them. The order in which the five phases occurred is well established, but the importance of the intervals between the phases is at present uncertain.

The inaugural data from the first systematic program of sea-ice observations in Kotzebue Sound, Alaska, in 2018 coincided with the first winter in living memory when the Sound was not choked with ice. The following winter of 2018–19 was even warmer and characterized by even less ice. Here we discuss the mass balance of landfast ice near Kotzebue (Qikiqtaġruk) during these two anomalously warm winters. We use in situ observations and a 1-D thermodynamic model to address three research questions developed in partnership with an Indigenous Advisory Council. In doing so, we improve our understanding of connections between landfast ice mass balance, marine mammals and subsistence hunting. Specifically, we show: (i) ice growth stopped unusually early due to strong vertical ocean heat flux, which also likely contributed to early start to bearded seal hunting; (ii) unusually thin ice contributed to widespread surface flooding. The associated snow ice formation partly offset the reduced ice growth, but the flooding likely had a negative impact on ringed seal habitat; (iii) sea ice near Kotzebue during the winters of 2017–18 and 2018–19 was likely the thinnest since at least 1945, driven by a combination of warm air temperatures and a persistent ocean heat flux.

Outlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.

The spatial distribution of basal water critically impacts the evolution of ice sheets. Current estimates of basal water distribution beneath the Greenland Ice Sheet (GrIS) contain large uncertainties due to poorly constrained boundary conditions, primarily from geothermal heat flux (GHF). The existing GHF models often contradict each other and implementing them in numerical ice-sheet models cannot reproduce the measured temperatures at ice core locations. Here we utilize two datasets of radar-detected basal water in Greenland to constrain the GHF at regions with a thawed bed. Using the three-dimensional ice-sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum GHF required to reach the bed to the pressure melting point, GHFpmp, at locations of radar-detected basal water. We identify parts of the central-east, south and northwest Greenland with significantly high GHFpmp. Conversely, we find that the majority of low-elevation regions of west Greenland and parts of northeast have very low GHFpmp. We compare the estimated constraints with the available GHF models for Greenland and show that GHF models often do not honor the estimated constraints. Our results highlight the need for community effort to reconcile the discrepancies between radar data, GHF models, and ice core information.

Speke Glacier, the best studied and largest single glacier in the Ruwenzori Range (Uganda, East Africa), was revisited in January 1990. A comparison of its present state with former observations reveals that its terminus receded 35–45 m between 1958 and 1977; since 1977 it has retreated more than 150 m. Nearly half the width of the snout has been lost, mainly on its western side, and the entire western section of the south-facing glacier has shrunk substantially. The observed fluctuation conforms with changes occurring on other tropical glaciers. Explanations concerning the reasons for the glacier recession are presented.

The growth of bonds between snow grains or ice spheres has been variously attributed to surface diffusion, volume diffusion, and evaporation–condensation. To distinguish among these possible mechanisms the unconfined compressive strength of two groups of snow samples was determined as a function of time. One group was allowed to sinter under atmospheric conditions while the other group was kept immersed in silicone oil. The much lower rate of strengthening of the latter group suggests that evaporation–condensation must be the major mechanism of mass transport in snow under atmospheric conditions. The possible magnitudes of the various mass transfer coefficients are discussed.

The accuracy of sea-ice motion products provided by the National Snow and Ice Data Center (NSIDC) and the Ocean and Sea Ice Satellite Application Facility (OSI-SAF) was validated with data collected by ice drifters that were deployed in the western Arctic Ocean in 2014 and 2016. Data from both NSIDC and OSI-SAF products exhibited statistically significant (p < 0.001) correlation with drifter data. The OSI-SAF product tended to overestimate ice speed, while underestimation was demonstrated for the NSIDC product, especially for the melt season and the marginal ice zone. Monthly Lagrangian trajectories of ice floes were reconstructed using the products. Larger spatial variability in the deviation between NSIDC and drifter trajectories was observed than that of OSI-SAF, and seasonal variability in the deviation for NSIDC was observed. Furthermore, trajectories reconstructed using the NSIDC product were sensitive to variations in sea-ice concentration. The feasibility of using remote-sensing products to characterize sea-ice deformation was assessed by evaluating the distance between two arbitrary positions as estimated by the products. Compared with the OSI-SAF product, relative errors are lower (<11.6%), and spatial-temporal resolutions are higher in the NSIDC product, which makes it more suitable for estimating sea-ice deformation.