Digital elevation models of the bed and surface of Unteraargletscher, Switzerland, are used to reconstruct the theoretical pattern of basal water drainage for the years 1927, 1947, 1961 and 1997, during which period the glacier was thinning and receding. The theoretical drainage pattern for 1997 compares well, in a broad sense, with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed. Changes in the basal water-flow pattern over the period 1927–97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry. Concurrent with the retreat and thinning of the glacier, the height of medial moraines increased, probably due to the insulating effect of the debris cover reducing the melt of the underlying ice. This increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface.

The Katla volcano, overlain by the Mýrdalsjökull glacier, is one of the most active and hazardous volcanoes in Iceland. Earthquakes show anomalous magnitude-frequency behaviour and mainly occur in two distinct areas: within the oval caldera and around Goðabunga, a bulge on its western flank. The seismicity differs between the areas; earthquakes in Goðabunga are low frequency and shallow whereas those beneath the caldera occur at greater depths and are volcano-tectonic. The seismicity shows seasonal variations but the rates peak at different times in the two areas. A snow budget model, which gives an estimate of the glacial loading, shows good correlation with seismic activity on an annual scale. Data recorded by the permanent network South Iceland Lowland (SIL), as well as by a temporary network, are used to invert for a 3D seismic velocity model underneath Eyjafjallajökull, Goðabunga and the Katla caldera. The tomography resolves a 15 km wide, aseismic, high-velocity structure at a depth of more than 4 km between the Eyjafjallajökull volcano in the west and the Katla volcano in the east. Anomalously low velocities are observed beneath the Katla caldera, which is interpreted as being a significantly fractured area of anomalously high temperature.

The observed ratio of removal of material by (i) scratches gouged by large clasts and (ii) polishing by debris suggests that the latter is the dominant form of bedrock erosion. We examine this with a multi-stage breakdown model of glacial debris, which includes active erosion by fines. These models suggest that a mother clast can, through the action of its daughter debris, erode several times its own volume of bedrock.

Till-sliding over bedrock is likely to be a potent source of scouring. By proposing a till/bedrock sliding law, we investigate the kinematics of sliding till bodies. Ice flow naturally tends to thin and extend till cover, even in the absence of longitudinal gradients in the applied stress. Thicker till cover has an increased effective pressure at its base, a lower sliding velocity and, for larger thicknesses, a decrease in sediment flux with thickness. This implies backward-moving kinematic waves and shocks. It is suggested that this is related to the blunt upstream faces of drumlins, and that drumlinization can be a consequence of debris sliding over bedrock.

Three receding glaciers on Spitsbergen were examined on the basis of a 1936 topographic map and field investigations during the summers of 1995 and 2001. Håbergbreen, the largest glacier, has undergone the most intensive recession due to its relatively low altitude. There are two important manifestations of glacial recession: (1) the retreating glaciers leave rocky outcrops in the upper or steeper mountain slopes, and (2) the edges of moving glacier tongues are being transformed into motionless ice-cored moraines in valleys. The glaciers under study have not been transformed into rock glaciers. The recession rate has been increasing since 1995, which can be interpreted as a result both of positive feedback initiated by 20th-century climate warming and of slight warming in the 1990s. The glaciers have not thawed enough in relation to the warming and rise of the equilibrium-line altitude (by at least 250–300 m since the beginning of the 20th century). Håbergbreen, already split up into four ice patches, will disappear without a sustained temperature decrease during the next few decades. Grumantbreen and Dryadbreen will survive as small mountain glaciers if winter snow precipitation does not increase.

A numerical model is used to study the spatial and temporal variability of ice thickness in the Arctic. The model is run to cyclo-stationary equilibrium, forced with daily varying geostrophic winds and monthly varying surface air temperatures from 1951 to 1990. Decadal-average winter ice-thickness fields exhibit a trend of increasing ice thickness in the East Siberian Sea and somewhat thicker ice overall in the 1980s. Inter-annual variability was largest in the Beaufort and East Siberian Seas and generally lower in the Laptev Sea and central Arctic. Spatial correlation patterns show that ice thickness at a point is correlated with ice thickness over a surrounding area of roughly 4 × 105 km2 with a correlation coefficient of 0.7. Temporal auto-correlation functions indicate that the total ice volume has a correlation time-scale of roughly 7 years, while the volume of ice between 2 and 5 m thick and the volume of ice less than 1 m thick have correlation times of roughly 2 years and 2 months, respectively.

Liligo glacier, in the central eastern Karakoram, Pakistan, is a small, south-to-north-flowing glacier situated in a transverse valley on the left (south) side of Baltoro glacier. New processing of satellite imagery enables a better quantification of terminus oscillations over the past 30 years. From the beginning of the 1970s to the beginning of the 21st century, Liligo glacier advanced about 2 km (60ma–1). The progress was characterized by a significant evolution of terminus morphology, similar to that observed on the same glacier during the advance event near the beginning of the 20th century, and to those of many other Karakoram glaciers. This suggests indications of a surge-type mechanism. Field observations performed in 2004 indicated there was probably no confluence at that time between Liligo and Baltoro glaciers and that a quiescent phase had started in the early years of the 21st century.

Minnesota is largely underlain by Precambrian crystalline bedrock that was weathered to an average depth of 30 m prior to Late Cretaceous time. The fresh-rock— weathered-rock interface is irregular, with as much as 45 m of relief. Weathering exploited joints, locally isolating meter-sized volumes of rock known as corestones. Variable amounts of residuum were removed through glaciation to leave (1) saprolite overlain by an in-situ Late Cretaceous soil profile; (2) partially eroded saprolite; and (3) undulating fresh rock surfaces (commonly mantled by rounded boulders) that display striae and glacial or fluvial polish.

Significant subglacial erosion of fresh bedrock is not required to form smoothly undulating bedrock surfaces with closed depressions; they may also form through removal of weathered bedrock and exposure of the weathering front. Large rounded boulders are not always shaped during transport; they may represent chemically rounded corestones resting at or near the bedrock source.

Unambiguous evidence for glacial erosion includes striae and streamlining of bedrock parallel to striae. Polish on rock can be created fluvially, and smoothed grooves and ridges in the rock may be chemically produced. Many rounded boulders found in glacial till and strewn on bedrock surfaces probably originated as corestones.

Photogrammetric digital elevation models (DEMs) are often used to derive and monitor surfaces in inaccessible areas. They have been used to monitor the spatial and temporal change of glacier surfaces in order to assess glacier response to climate change. However, deriving photogrammetric DEMs of steep mountainous topography where the surface is often obscured by regions of deep shadow and snow is particularly difficult. Assessing the quality of the derived surface can also be problematic, as high-accuracy ground-control points may be limited and poorly distributed throughout the modelled area. We present a method of assessing the quality of a derived surface through a detailed sensitivity analysis of the DEM collection parameters through a multiple input failure warning model (MIFWM). The variance of a DEM cell elevation is taken as an indicator of surface reliability allowing potentially unreliable areas to be excluded from further analysis. This analysis allows the user to place greater confidence in the remaining DEM. An example of this method is presented for a small mountain glacier in Svalbard, and the MIFWM is shown to label as unreliable more DEM cells over the entire DEM area, but fewer over the glacier surface, than other methods of data quality assessment. The MIFWM is shown to be an effective and easily used method for assessing DEM surface quality.

A technique proposed by Hooke and Iverson (1995) to identify deformed subglacial sediments is reviewed and tested, based on two main objectives. First, an investigation of whether the fractal dimension can distinguish between non-deformed and deformed facies; for which we compare supraglacial and subglacial facies explicitly. Second, an evaluation of whether the fractal dimension can be used as a diagnostic criteria to discriminate between different styles and degrees of basal deformation. This is tested using a range of sediments from the deformation continuum suggested by Hart and Boulton (1991b). Sixteen subglacial samples were selected from Quaternary sites in England and three supraglacial samples from the modern Haut Glacier d’Arolla, Switzerland. The mean fractal dimension for the subglacial diamicton matrix facies was 2.92, similar to findings of 2.90 by Hooke and Iverson (1995) for their basal tills. The supraglacial facies displayed a mean fractal dimension of 2.83, which is unusually high for facies which are assumed to be undeformed. A Mann—Whitney U test showed that fractal dimensions of supraglacial and subglacial diamicton matrix facies were not significantly different. No significant difference was found between the fractal dimensions of the different tectonic facies within the subglacial group. It may be impossible to separate the subglacial and supraglacial facies because of complex debris paths within the glacier. Grain fracture or parent lithology may affect the particle-size distribution of subglacial facies.

A three-dimensional time-dependent thermomechanical ice-sheet model was used together with a two-level (snow-accumulation/runoff) mass-balance model to investigate the Quaternary ice sheets of the Northern Hemisphere. The model freely generates the ice-sheet geometry in response to specified changes in surface temperature and mass balance, and includes bedrock adjustment, basal sliding and a full temperature calculation within the ice. The mass-balance parameterization makes a distinction between snowfall and melting. Yearly snowfall rates depend on the present precipitation distribution, and are varied proportionally to changes in surface temperature and the moisture content of the air. The ablation model is based on the positive-degree-day method, and distinguishes between ice and snow melting. This paper discusses steady-slate characteristics, conditions for growth and retreat, and response time-scales of ice sheets as a function of a prescribed lowering of summer temperature. Most notably, the modelled extents of the Eurasian ice sheet for a summer temperature lowering of 6–7 K and of the Laurentide ice sheet for a cooling of 9–10 K are in reasonable agreement with most reconstructions based on geological evidence, except for the presence of a large ice sheet stretching from Alaska across the Bering Strait to most of eastern Siberia. In addition, wet basal conditions turned out to be always confined to the margin, whereas central areas in these reconstructions remained always cold-based. This is of relevance for processes involving reduced basal traction.

We estimate all the individual glacier area and volume changes in High Mountain Asia (HMA) by 2050 based on Randolph Glacier Inventory (RGI) version 4.0, using different methods of assessing sensitivity to summer temperatures driven by a regional climate model and the IPCC A1B radiative forcing scenario. A large range of sea-level rise variation comes from varying equilibrium-line altitude (ELA) sensitivity to summer temperatures. This sensitivity and also the glacier mass-balance gradients with elevation have the largest coefficients of variability (amounting to ~50%) among factors examined. Prescribing ELA sensitivities from energy-balance models produces the highest sea-level rise (9.2 mm, or 0.76% of glacier volume a–1), while the ELA sensitivities estimated from summer temperatures at Chinese meteorological stations and also from 1°x1° gridded temperatures in the Berkeley Earth database produce 3.6 and 3.8 mm, respectively. Different choices of the initial ELA or summer precipitation lead to 15% uncertainties in modelled glacier volume loss. RGI version 4.0 produces 20% lower sea-level rise than version 2.0. More surface mass-balance observations, meteorological data from the glaciated areas, and detailed satellite altimetry data can provide better estimates of sea-level rise in the future.

Popocatépetl (19°02’ N, 98°62’W; 5424 m) is one of the largest active stratovolcanoes in the Transmexican Volcanic Belt. A glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in December 1994. In our study, we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity (1994–2002), using photogrammetric treatment of 20 pairs of aerial photographs. The results indicate that from November 1997 to December 2002, the glacier released approximately 3 967 000 m3 of water. A period of intense glacier melting occurred from 4 November 2000 to 15 March 2001 during which time 717 000 m3 of water was released. Much of the melting was attributed to the pyroclastic flow that took place on 22 January 2001 and produced a 14.2 km lahar with 68 000 m3 of water. Among the many types of volcanic events, pyroclastic flows were the most effective in causing sudden snowmelt, although small explosions were also effective since they deposited incandescent material on the glacier. The collapse of the plinian columns covered the glacier with pyroclasts and increased its volume. The existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention.

Surface melt on a glacier can perturb the glaciochemical record beyond the natural variability. While the centre of the Greenland ice sheet is usually devoid of surface melt, many high-Arctic and alpine ice cores document frequent summertime melt events. Current hypotheses interpreting melt-affected ice-core chemistry rely on preferential elution of certain major ions. However, the precise nature of chemistry alteration is unknown because it is difficult to distinguish natural variability from melt effects in a perennially melt-affected site. We use eight trace-element snow chemistry records recovered from Summit, Greenland, to study spatial variability and melt effects on insoluble trace chemistry and physical stratigraphy due to artificially introduced meltwater. Differences between non-melt and melt-affected chemistry were significantly greater than the spatial variability in chemistry represented by nearest-neighbour pairs. Melt-perturbed trace elements, particularly rare earth elements, retained their seasonal stratigraphies, suggesting that trace elements may serve as robust chemical indicators for annual layers even in melt-affected study areas. Results suggest trace-element transport via meltwater percolation will deposit eluted material down-pit in refrozen areas below the nearest-surface chemistry peak. In our experiments, snow chemistry analyses are more sensitive to melt perturbations than density changes or unprocessed near-infrared digital imagery.

Seismic signals of avalanches, related video images and numerical models were compared to improve the characterization of avalanche phenomena. Seismic data and video images from two artificially released avalanches were analysed to obtain more information about the origin of the signals. Image processing was used to compare the evolution of one avalanche front and the corresponding seismic signals. A numerical model was also used to simulate an avalanche flow in order to obtain mean- and maximum-velocity profiles. Prior to this, the simulated avalanche was verified using video images. The results indicate that the seismic signals recorded correspond to changes in avalanche type and path slope, interaction with obstacles and to phenomena associated with the stopping stage of the avalanche, suggesting that only part of the avalanche was recorded. These results account for the seismic signals previously obtained automatically in a wide avalanche area.

Sea ice is composed of columnar-shaped grains. To investigate the influence of the loading direction on the uniaxial compressive strength and failure processes of sea ice, field experiments were performed with first-year level ice. Loads were applied both horizontally (parallel to the grain columns) and vertically (across the grain columns) with various nominal strain rates. Two failure modes have been observed: a ductile failure mode at low nominal strain rates, and a brittle failure mode at high nominal strain rates. However, the failure pattern of sea ice was clearly dependent on the loading direction. At low nominal strain rates (ductile failure mode), the sea-ice samples yielded due to the development of wing cracks under horizontal loading and due to splaying out at one end under vertical loading. When sea ice fails in the ductile mode, the deformation is driven by grain boundary sliding under horizontal loading and by grain decohesion and crystal deflection under vertical loading. At high nominal strain rates (brittle failure mode), the sea-ice samples failed in shear faulting under horizontal loading and in cross-column buckling under vertical loading. The nominal strain rate at the brittle–ductile transition zone is about ten times higher under vertical loading.

Interferometric synthetic aperture radar data show that Devon Ice Cap (DIC), northern Canada, is drained through a network of 11 glacier systems. More than half of all ice discharge is through broad flows that converge to the southeast of the ice cap, and these are grounded well below sea level at their termini. A calculation of the ice-cap mass budget reveals that the northwestern sector of DIC is gaining mass and that all other sectors are losing mass. We estimate that a 12 489 km2 section of the main ice cap receives 3.46±0.65 Gt of snowfall each year, and loses 3.11±0.21 Gt of water through runoff, and 1.43±0.03 Gt of ice through glacier discharge. Altogether, the net mass balance of DIC is –1.08±0.67 Gt a–1. This loss corresponds to a 0.003 mma–1 contribution to global sea levels, and is about half the magnitude of earlier estimates.

The Antarctic Impulsive Transient Antenna (ANITA) balloon experiment was designed to detect radio signals initiated by high-energy neutrinos and cosmic ray (CR) air showers. These signals are typically discriminated by the polarization and phase inversions of the radio signal. The reflected signal from CRs suffer phase inversion compared to a direct ‘tau neutrino’ event. In this paper, we study subsurface reflection, which can occur without phase inversion, in the context of the two anomalous up-going events reported by ANITA. It is found that subsurface layers and firn density inversions may plausibly account for the events, while ice fabric layers and wind ablation crusts could also play a role. This hypothesis can be tested with radar surveying of the Antarctic region in the vicinity of the anomalous ANITA events. Future experiments should not use phase inversion as a sole criterion to discriminate between down-going and up-going events, unless the subsurface reflection properties are well understood.

The internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a−1 ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns.

Daily precipitation fields and annual means from the European Centre for Medium-range Weather Forecasts re-analysis exercise are used to examine the distribution and variability of precipitation across the Antarctic Peninsula. The annual mean precipitation field from the model agrees well with the available ice-core data and suggests that the maximum accumulation for the area is on the western side of the barrier at about the 200 m level where the annual total is close to 1.3 m w.e. The Peninsula is shown to be a very effective barrier to the zonal movement of precipitating weather systems, which results in quite different atmospheric flow regimes being responsible for significant precipitation events on other side of the divide. Frontal depressions are the primary source of large daily snowfall totals on both sides of the Peninsula. On the southern coast of the Bellingshausen Sea, major snowfall events are often linked to strong northerly flow when the atmospheric circulation is blocked. Predominantly northerly flow is also responsible for significant snowfall on the Ronne Ice Shelf, which often occurs in association with lee cyclogenesis events to the east of the- Peninsula.

All parts of a two-dimensional, isothermal, stationary marine glacier (grounded ice sheet, ice shelf and transition zone) with constant viscosity are analysed by perturbation methods. In so doing, all zones of different flow patterns can be considered separately. Correlations between spatial scales for all parts can be expressed in terms of the typical ice-surface slope distant from the ocean, which reflects exterior conditions of the glacier’s existence. In considering the ice-sheet–ice-shelf transition zone, a small parameter characterizing the difference between ice and water densities is used. Such an analysis allows us to find boundary conditions at the grounding line for the grounded ice mass. Glacier-surface profiles are determined by numerical methods. The grounding-line position found by using the boundary conditions derived in this paper differs from that obtained by using Thomas and Bentley’s (1978) boundary conditions by about 10% of the grounded ice-stream length.