Oxygen isotopic and soluble ionic measurements made on snow-pit (2 m depth) and firn-core (12.4 m depth) samples recovered from the accumulation zone (5100 m) of Inilchek glacier (43° N, 79° E) provide information on recent (1992–98) climatic and environmental conditions in the central Tien Shan region of central Asia. The combined 14.4 m snow-pit/firn-core profile lies within the firn zone, and contains only one observed melt feature (10 m temperature = −12°C). Although some post-depositional attenuation of the sub-seasonal δ18O record is possible, annual cycles are apparent throughout the isotope profile. We therefore use the preserved δ18O record to establish a depth/age scale for the core. Mean δ18O values for the entire core and for summer periods are consistent with δ18O/temperature observations, and suggest the δ18O record provides a means to reconstruct past changes in summer surface temperature at the site. Major-ion (Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3−, SO42−) data from the core demonstrate the dominant influence of dust deposition on the soluble chemistry at the site, and indicate significant interannual variability in atmospheric-dust loading during the 1990s. Anthropogenic impacts on NH4+ concentrations are observed at the site, and suggest a summer increase in atmospheric NH4+ that may be related to regional agricultural (nitrogen-rich fertilizer use) activities.

Results from the Heinrich Event Intercomparison (HEINO) topic of the Ice-Sheet Model Intercomparison Project (ISMIP) are presented. ISMIP HEINO was designed to explore internal large-scale ice-sheet instabilities in different contemporary ice-sheet models. These instabilities are of interest because they are a possible cause of Heinrich events. A simplified geometry experiment reproduces the main characteristics of the Laurentide ice sheet, including the sedimented region over Hudson Bay and Hudson Strait. The model experiments include a standard run plus seven variations. Nine dynamic/thermodynamic ice-sheet models were investigated; one of these models contains a combination of the shallow-shelf (SSA) and shallow-ice approximation (SIA), while the remaining eight models are of SIA type only. Seven models, including the SIA–SSA model, exhibit oscillatory surges with a period of ∼1000 years for a broad range of parameters, while two models remain in a permanent state of streaming for most parameter settings. In a number of models, the oscillations disappear for high surface temperatures, strong snowfall and small sediment sliding parameters. In turn, low surface temperatures and low snowfall are favourable for the ice-surge cycles. We conclude that further improvement of ice-sheet models is crucial for adequate, robust simulations of cyclic large-scale instabilities.

As ice streams flow into the Ross Ice Shelf, West Antarctica, their bed coupling transitions from weak to transient to zero as the ice goes afloat. Here we explore the nature of the bed across these crucial grounding zones using ice-penetrating radar. We collected several ground-based 2 MHz radar transects across the grounding zones of Whillans and Kamb Ice Streams and inferred bed-reflectivity changes from in situ measurements of depth-averaged dielectric attenuation, made possible by the observation of both primary and multiple bed echoes. We find no significant change in the bed reflectivity across either grounding zone. Combined with reflectivity modeling, this observation suggests that a persistent layer of subglacial water (>∼0.2 m) is widespread several kilometers upstream of the grounding zone. Our results are consistent with previous inferences of gradual grounding zones across this sector of the Ross Ice Shelf from airborne radar and satellite altimetry. Separately, the only clear bed-reflectivity change that we observed occurs ∼40 km downstream of the Kamb Ice Stream grounding zone, which we attribute to the onset of marine ice accretion onto the base of the ice shelf. This onset is much nearer to the grounding zone than previously predicted.

We have analyzed InSAR data from the ERS-1/ERS-2 tandem mission, to study the ice dynamics of Vatnajökull, Iceland, during jökulhlaups from the Skaftá cauldrons and the Grímsvötn geothermal area, which drained under the Tungnaárjökull and Skeiðarárjökull outlets, respectively. During the initial phase of a Grímsvötn jökulhlaup in March 1996, the velocity of Skeiðarárjökull increased up to three-fold (relative to observed velocities in December 1995) over an area up to 8 km wide around the subglacial flood path. Accumulation of water was observed at one location in the flood path. During a small jökulhlaup from the Skaftá cauldrons in October 1995 the velocity on Tungnaárjökull increased up to four-fold over a 9 km wide area. The velocity increase was observed 1.5 days before the floodwater was detected in the river Skaftá. A reduced glacier speed as the flood peaked in Skaftá indicates evolution of the subglacial drainage system from sheet to tunnel flow. The glacier acceleration and local uplift, observed in the early phase of both jökulhlaups, supports the concept that increased water inflow in a narrow tunnel system causes water pressure to rise and forces water into areas outside the channels, thus reducing the coupling of ice with the glacier bed.

The salinity distribution in multi-year sea ice is dependent on the ice topography and cannot be adequately represented by a single average profile. The cores collected from areas beneath surface hummocks generally showed a systematic increase in salinity with depth from 0‰ at the surface to about 4‰ at the base. The cores collected from areas beneath surface depressions were much more saline and displayed large salinity fluctuations.

Salinity observations from sea ice of varying thicknesses and ages collected at various Arctic and sub-Arctic locations revealed a strong correlation between the average salinity of the ice and the ice thickness h. For salinity samples collected from cold sea ice at the end of the growth season, this relationship can be represented by two linear equations: ; . It is suggested that the pronounced break in slope at 0.4 m is due to a change in the dominant brine drainage mechanism from brine expulsion to gravity drainage. A linear regression for the data collected during the melt season gives . An annual cyclic variation of the mean salinity exists for multi-year sea ice. The mean salinity reaches a maximum at the end of the growth season and a minimum at the end of the melt season.

Remote-sensing and GIS techniques in conjunction with field investigations show how glacier mass loss has led to the rapid growth of Linggo Co, a glacier-fed lake on the central Tibetan Plateau, which has expanded by 21.3% in area between 1974 and 2010, with a lake-level rise of ˜11.2m. The lake volume of Linggo Co increased at a rate of 0.02 × 106, 42.67 × 106 and 65.8 × I06m3a-1 during the periods 1974-92, 1992-99 and 1999-2010, respectively. Other nonglacier-fed lakes in the vicinity (i.e. Longwei Co, Amur Co and Darngo Co Ngion) shrank considerably from the early 1970s to 1992 and then expanded from 1992 to 2010. Despite being in the same climate region, Linggo Co and the non-glacier-fed lakes have differed in response to climate change. The glaciers in the catchment of Linggo Co retreated by 2.4% in area between 1974 and 2007, and their mean thickness decreased by 6.19 ± 1.91 m between 1974 and 2000, with an associated glacier meltwater runoff of (7.52 ± 2.32) × 108 m3. The results indicate that glacier mass loss had a significant impact on the growth of Linggo Co over the past 40 years.

Bedrock overdeepenings exposed by continued glacial retreat can store precipitation and meltwater, potentially leading to the formation of new proglacial lakes. These lakes may pose threats of glacial lake outburst floods (GLOFs) in high mountain areas, particularly if new lakes form in geomorphological setups prone to triggering events such as landslides or moraine collapses. We present the first complete inventory for future glacial lakes in High Mountain Asia by computing the subglacial bedrock for ~100 000 glaciers and estimating overdeepening area, volume and impact hazard for the larger potential lakes. We detect 25 285 overdeepenings larger than 104 m2 with a volume of 99.1 ± 28.6 km3 covering an area of 2683 ± 773.8 km2. For the 2700 overdeepenings larger than 105 m2, we assess the lake predisposition for mass-movement impacts that could trigger a GLOF by estimating the hazard of material detaching from surrounding slopes. Our findings indicate a shift in lake area, volume and GLOF hazard from the southwestern Himalayan region toward the Karakoram. The results of this study can be used for anticipating emerging threats and potentials connected to glacial lakes and as a basis for further studies at suspected GLOF hazard hotspots.

The response of glaciers to climate change has major implications for sea-level change and water resources around the globe. Large-scale glacier evolution models are used to project glacier runoff and mass loss, but are constrained by limited observations, which result in models being over-parameterized. Recent systematic geodetic mass-balance observations provide an opportunity to improve the calibration of glacier evolution models. In this study, we develop a calibration scheme for a glacier evolution model using a Bayesian inverse model and geodetic mass-balance observations, which enable us to quantify model parameter uncertainty. The Bayesian model is applied to each glacier in High Mountain Asia using Markov chain Monte Carlo methods. After 10,000 steps, the chains generate a sufficient number of independent samples to estimate the properties of the model parameters from the joint posterior distribution. Their spatial distribution shows a clear orographic effect indicating the resolution of climate data is too coarse to resolve temperature and precipitation at high altitudes. Given the glacier evolution model is over-parameterized, particular attention is given to identifiability and the need for future work to integrate additional observations in order to better constrain the plausible sets of model parameters.

Modelling the heat flow in small, cold high-altitude glaciers is important for the interpretation of paleoclimatic data from ice cores. Coupled glacier-flow and heat-flow models are presented that incorporate the densification, heat advection and possible phase transitions at the permafrost boundaries within the bedrock. Marked bends observed in the temperature profiles from two recent boreholes on Colle Gnifetti, Swiss Alps, are interpreted with the help of a transient heat-flow model, driven with a temperature history. The conclusion is that substantial warming of the mean firn temperature at shallow depths has taken place over the last few decades. This has not been observed before in cold-firn regions of the Alps. Modelled heat fluxes in the Monte Rosa massif are strongly influenced by the mountain topography. This leads to a spatial variability of the temperature gradient near the glacier base which has been observed in boreholes to the bedrock. In order to match the measured temperature profiles in the glacier, the vertical heat flux at great depth must be set to an extremely low value. It is shown with the help of the transient heat-flow model that this is a paleoclimatic effect, possibly enhanced by a degrading permafrost base.

This paper presents a glacier ice-flow model that simulates changes to alpine glaciers of various sizes and their runoff response to climate change in the Yili river basin in the Tien Shan mountains, northwestern China. It is suggested that the sensitivity of glaciers to climatic change is determined by glacier size. The change in glacial runoff does not keep pace with climatic change. As climate warms and glaciers retreat, the glacier runoff tends to increase and then decrease. The runoff peak and its timing depend not only on glacier size but also on the rate of air-temperature rise.

Pressure and tracer measurements in boreholes drilled to the bottom of Ice Stream B, West Antarctica, are used to obtain information about the basal water conduit system in which high water pressures are developed.These high pressures presumably make possible the rapid movement of the ice stream. Pressure in the system is indicated by the borehole water level once connection to the conduit system is made. On initial connection, here also called “breakthrough” to the basal water system, the water level drops in a few minutes to an initial depth in the range 96–117 m below the surface. These water levels are near but mostly somewhat deeper than the floation level of about 100 m depth (water level at which basal water pressure and ice overburden pressure are equal), which is calculated from depth-density profiles and is measured in one borehole. The conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed; the thickness of the gap δ has to be about 2 mm to account for the water-level drop on breakthrough, and about 4 mm to fit the results of a salt-tracer experiment indicating downstream transport at a speed of 7.5 mm s−1. The above gap-conduit model is, however, ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole, and also by the large hole-to-hole variation in measured basal pressure, which if present in a gap-conduit system with δ = 2 or 4 mm would result in unacceptably large local water fluxes. An alternative model that avoids these objections, called the “gap opening” model, involves opening a gap as injection proceeds: starting with a thin film, the injection of water under pressure lifts the ice mass around the borehole, creating a gap 3 or 4mm wide at the ice/bed interface. Evaluated quantitatively, the gap-opening model accounts for the volume of water that the basal water system accepts on breakthrough, which obviates the gap-conduit model. In order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits, of which the most promising type is the “canal” conduit proposed theoretically by Walder and Fowler (1994): flat, low conduits incised into the till, ∼0.1 m deep and perhaps ∼1 m wide, with a flat ice roof. The basal water-pressure data suggest that the canals are spaced ∼50–300 m apart, much closer than R-tunnels would be. The deepest observed water level, 117 m, is the most likely to reflect the actual water pressure in the canals, corresponding to a basal effective pressure of 1.6 bar. In this interpretation, the shallower water levels are affected by loss of hydraulic head in the narrow passageway (s) that connect along the bed from borehole to canal(s). Once a borehole has frozen up and any passageways connecting with canals have become closed, a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till, given enough time for pressure equilibration. This pressure varies considerably with time, over the equivalent water-level range from 100 to 113 m. Basal pressure sensors 500 m apart report uncorrelated variations, whereas sensors in boreholes 25 m араrt report mostly (but not entirely) well-correlated variations, of unknown origin. In part of the record, remarkable anticorrelated variations are interspersed with positively correlated ones, and there are rare, abrupt excursions to extreme water levels as deep as 125 m and as shallow as 74 m. A diurnal pressure fluctuation, intermittently observed, may possibly be caused by the ocean tide in the Ross Sea. The lack of any observed variation in ice-stream motion, when large percentagewise variations in basal effective pressure were occurring according to our data, suggests that the observed pressure variations are sufficiently local, and so randomly variable from place to place, that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed.

The present study was carried out with a view to quantifying the effects of the main parameters ot temperature-gradient metamorphism. Cold-room simulation tests showed crystal growth to be an increasing function of the temperature-gradient modulus with a lower limit of around 0.25 deg/cm. This growth also proved to be a function of temperature itself reaching a maximum at around –5°C Furthermore the shape of depth-hoar crystals was also shown to depend on temperature and to resemble approximately that obtained when crystals are formed in the atmosphere. Temperature-gradient metamorphism is observed to take place at constant density. Increase in crystal size is a decreasing function of density with a lower limit of around 150 kg/m3, below which destructive metamorphism occurs accompanied by packing (similar to ET metamorphism): the upper limit is situated at approximately 350 kg/m3 and no depth-hoar crystals occur above this value. The series of Cold-room simulations enabled a highly simplified model of crystal growth to be constructed.

Preferred c-axis orientations are present in the firn at Siple Dome, West Antarctica, and recrystallization begins as shallow as 200 m depth in ice below –20°C, based on digital analysis of c-axis fabrics, grain-sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer-long Siple Dome ice core. The shallowest section analyzed, from 22 m, shows clustering of c axes toward the vertical. By 200 m depth, girdle fabric and other features of recrystallized ice are evident in layers (or regions), separated by layers (regions) of typically finer-grained ice lacking evidence of recrystallization. Ice from about 700–780m depth, which was deposited during the last ice age, is especially fine-grained, with strongly vertical c axes, but deeper ice shows much larger crystals and strong evidence of recrystallization. Azimuthal asymmetry of some c-axis fabrics, trends in grain-size, and other indicators reveal additional information on processes and history of ice flow at Siple Dome.

Glacier changes in the Jankar Chhu Watershed (JCW) of Chandrabhaga (Chenab) basin, Lahaul Himalaya were worked out based on Corona and Sentinel 2A images between 1971 and 2016. The JCW consists of 153 glaciers (>0.02 km2) with a total area of 185.6 ± 3.8 km2 that include 82 glaciers with debris-covered ablation zone, comprising 10.9% of the total glacierized area as in 2016. Change analysis based on Corona (1971), Landsat (2000) and Sentinel 2A (2016) was restricted to 127 glaciers owing to the presence of cloud cover on 26 glaciers in 1971. A subset of glaciers was also mapped using Landsat Thematic Mapper (TM; 1989) image. The total glacier area decreased by 14.7 ± 4.3 km2 (0.3 ± 0.1 km2 a−¹). The number of glaciers in the JCW increased by four between 1971 and 2016 due to fragmentation. More recently (2000–16), recession rate has increased. Clean-ice area decreased by 21.8 ± 3.8 km2 (0.5 ± 0.1 km2 a−¹) while debris-covered ice increased by 7.2 ± 0.4 km2 (0.2 ± 0.01 km2 a−¹). Field observations of select glaciers also support derived recession trend in the JCW. Retreat rates in the JCW have been observed to be much lower than previously reported.

Using a snow/atmosphere coupled model, the evolution of the surface and near-surface snow temperature is modeled at Dome C, Antarctica, during the period 20–30 January 2010. Firstly, the detailed multilayer snow model Crocus is run in stand-alone mode, with meteorological input forcing data provided by local meteorological observations. The snow model is able to simulate the evolution of surface temperature with good accuracy. It reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well. Secondly, a fully coupled 3-D snow/atmosphere simulation is performed with the AROME regional meteorological model, for which the standard single-layer snow parameterization is replaced by Crocus. In spite of a poor simulation of clouds, the surface and near-surface snow temperatures are correctly simulated, showing neither significant bias nor drifts during the simulation period. The model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower. This study highlights the potential of snow/atmosphere coupled models over the Antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions.

Recent acceleration and thinning of Thwaites Glacier, West Antarctica, motivates investigation of the controls upon, and stability of, its present ice-flow pattern. Its eastern shear margin separates Thwaites Glacier from slower-flowing ice and the southern tributaries of Pine Island Glacier. Troughs in Thwaites Glacier’s bed topography bound nearly all of its tributaries, except along this eastern shear margin, which has no clear relationship with regional bed topography along most of its length. Here we use airborne ice-penetrating radar data from the Airborne Geophysical Survey of the Amundsen Sea Embayment, Antarctica (AGASEA) to investigate the nature of the bed across this margin. Radar data reveal slightly higher and rougher bed topography on the slower-flowing side of the margin, along with lower bed reflectivity. However, the change in bed reflectivity across the margin is partially explained by a change in bed roughness. From these observations, we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties. Given the potential for future increases in ice flux farther downstream, the eastern shear margin may be vulnerable to migration. However, there is no evidence that this margin is migrating presently, despite ongoing changes farther downstream.

During the outburst flood of a glacier-dammed lake on Gornergletscher, Switzerland, in July 2004, the drained lake water triggered anomalous glacier motion. At the onset of the outburst, the ice-flow direction in the vicinity of the lake became closer to the central flowline. When the lake discharge magnitude decreased, the flow direction altered such that the ice moved back to the azimuth of the initial motion. At one of the survey points, where the ice flows parallel to the central flowline, the ice accelerated along the pre-event flow direction followed by a 180° backward motion that lasted over 2 days. These observations indicate the impact of the lake outburst on the subglacial and englacial stress conditions; however, the reversal in the flow direction is difficult to explain by drawing on our current understanding of glacier mechanics. The timing and the timescale of the flow-direction changes suggest that the elastic glacier motion and its rebound played a role under the rapidly changing stress conditions, but the Young’s modulus of ice is too large to cause the observed ice motion. Other processes, including basal separation and subglacial sediment deformation, are discussed as possible mechanisms for the reversal of the ice motion.

We describe an automated method to generate an inventory of glaciers and glacier morphometry from a digital topographic database containing glacier boundaries and a digital elevation model for British Columbia, Canada. The inventory contains over 12 000 glaciers with a total cumulative area that exceeds 25 000 km2, based on mapping from aerial photographs circa the mid-1980s. We use the inventory to examine dimensional characteristics among glaciers, namely the scaling relations between glacier length, width and area. Glacier length is a good predictor of glacier area, and its predictive ability improves when glaciers are stratified by the number of up-valley accumulation basins. The spatial pattern of glacier mid-range altitude parallels glaciation limits previously mapped for British Columbia and similarly reflects large-scale controls of orographic precipitation and continentality. The inventory is also used to refine models that relate glacier mid-range and terminus altitudes to regional position, aspect and, in the case of terminus altitudes, an index of glacier shape. Relations between glacier altitude limits and controlling spatial and topographic factors are used to make further climatic and mass-balance inferences from the glacier inventory.

A method for calculation of “maximum” avalanche run–out distance based on topographic parameters only is described. 423 well–known avalanches have had their maximum extent registered. The average gradient of avalanche path (α–angle), measured between the highest point of rupture and outer end of avalanche deposit is used as description of avalanche run–out. The topographic parameters which determine α are described.

A regression analysis of 111 avalanche paths based on 8 terrain parameters is performed, applying 26 independent combinations of these parameters as variables. The four best combinations of variables are used. These variables are: second derivative y’’ of avalanche slope described by a second–degree function, average gradient of avalanche track β, total vertical displacement of the avalanche H, and gradient of rupture zone θ.

The equation has a correlation coefficient of 0.95 and standard deviation of 2.3°. This relationship makes possible a fairly accurate prediction of avalanche run–out distance.

Wind-blown snow represents an age-old problem in the applied glaciology of most higher-latitude regions, but its physical intricacies first received attention in esoteric discussions on the long-term mass balance of polar ice sheets (Loewe, 1933, 1956). Measurements on the uniform unlimited surface of such ice sheets have shown good agreement, at least over a limited height range, with estimates for the concentration and flux of drift snow as a function of height and wind velocity based on turbulence theory. An alternative theory, developed concurrently from wind-tunnel results and field observations in Siberia, is discussed on the basis of its most recent exposition (Dyunin, 1974). Basic questions requiring further study include drift-snow concentrations at considerable heights, drift evaporation, and electrical phenomena. The main practical aspects of snow drift relate to the prevention of excess accumulation on roads, railway lines, and avalanche slopes; and to the encouragement of accumulation in fields and forests, and other locations where frost protection and/or storage of water is desired. The methods used are reviewed; they are beginning to rely on physical concepts and theories rather than solely on empirical formulae derived from engineering experiments.

In regions of positive surface mass balance, buildings and other structures tend to become obliterated by snow drift. An important factor of this process is the fall-out of snow in the retarded flow on the windward side of the structure. Some recent attempts to measure and calculate that fall-out are discussed.