Previous observations have shown spatial covariances between microwave emission from Antarctic firn at 6 cm wavelength, physical firn temperature and firn-density stratification. Such observations motivate us to understand the physics underlying such covariances and, based on that understanding, to develop estimation methods for firn in which density, and therefore dielectric permittivity, varies randomly in discrete layers with mean thicknesses on the order of centimeters. The model accounts for depth profiles of the physical temperature, mean density and variance of random density fluctuations from layer to layer. We also present a procedure to estimate emission-model input parameters objectively from in situ density-profile observations, as well as uncertainties in the input parameters and corresponding uncertainties in theoretical brightness-temperature predictions. We compare emission-model predictions with ground-based observations at four diverse sites in Antarctica which span a range of accumulation rates and other parameters. We use coincident characterization data to estimate model inputs. At two sites, layered-medium emission-model predictions based on the most probable input parameters (i.e. with no model tuning) agree with observations to within 3.5% for incidence angles≤50°. Corresponding figures for the other two sites are 7.5% and 10%. However, uncertainties in the input parameters are substantial due to the limited length and depth resolution of the characterization data. Uncertainties in brightness-temperature predictions are correspondingly substantial. Thus brightness-temperature predictions for the last-mentioned sites based on only slightly less probable input parameters are also in close agreement with observations. The significance of agreements and discrepancies could be clarified using characterization measurements with finer depth resolution.

Over 75 000 surface-velocity measurements are extracted from sequential satellite imagery of Ice Streams D and E to reveal a complex pattern of flow not apparent from previous measurements. Horizontal and vertical strain rates, calculated from surface velocity, indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher. Ten airborne-radar profiles and one surface-based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream. Improved data-collection methods increase data density, substantially reducing random errors in velocity. However, systematic errors continue to limit the ability of the flux-differencing technique used here to resolve local variations in mass balance. Nevertheless, significant local variations in mass balance are revealed, while, overall, Ice Streams D and E are in approximate equilibrium. An earlier estimate of the net mass balance for Ice Stream D is improved.

Аn excellent photographic database, comprising 12 sets of vertical aerial photographs taken between 1948 and 1993, has enabled the structural glaciology of surge-type Variegated Glacier, Alaska, U.S.A., tо be analyzed for a period that spans two surge cycles and includes the effects of three surges. The glacier-wide patterns of crevasse development at the end of each of these surges, which occurred in 1947–48, 1964–65 and 1982–83, were remarkably similar, despite differences in surge intensities and extents. At the end of each surge a three-fold longitudinal zonation of crevasse orientation characterised that part of the glacier that had been affected by surge activity. This zonation comprises: (i) transverse crevasses in a narrow upper zone, (ii) superimposed longitudinal and transverse crevasses in an extensive middle zone, and (iii) longitudinal crevasses in a narrow lower zone. The main difference between patterns produced by successive surges was small variations in the extent оf the three zones. During quiescence, the most intense crevasse development occurs in the upper glacier in the latter part of quiescence, and is a function of increasingly steep down-glacier velocity gradients developing in the buildup to the impending surge. Some crevassing also develops in the central part of the glacier in mid-quiescence that is not related to the surge nature of the glacier, but to normal flow processes over bedrock. There is no structural evidence to indicate that any of the tributaries of Variegated Glacier surge. This observation suggests that the bulb-like loops in the medial moraines at Variegated Glacier form during quiescence as a result of the steady flow of the tributaries into the stagnant trunk glacier, rather than as a result of tributary surges.

This paper describes the development and testing of a distributed surface energy-balance model used to calculate rates of surface melting at Haut Glacier d’Arolla, Valais, Switzerland. The model uses a digital elevation model (DEM) of the glacier surface and surrounding topography together with meterological data collected at a site in front of the glacier to determine hourly or daily totals of the energy-balance components and hence of melting over the entire surface of the glacier with a spatial resolution of 20 m. The model can also be used to determine temporal and spatial variations in snow depth, snow-line position and glacier surface albedo. Calculations from the model are compared with observations made along the glacier centre line 1990, and in general the model performs very well. The correlation coefficients between calculated and measured snow-line elevation, albedo and ablation are 0.99, 0.85 and 0.81, respectively. The main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model.

Over a floating glacier ice tongue or an ice shelf, the glacier motion measured by a single, repeat-pass, radar interferogram is difficult to analyze, because the long-term, steady motion of the ice is intermixed with its cyclic, downward motion induced by tidal forcing. Multiple interferograms and a quadruple-difference technique are necessary to separate the tidal signal from the long-term, steady motion of the ice. An example of application of this technique is given here using ERS-1 radar images of Petermann Gletscher, a major outlet glacier of northern Greenland. Tidal displacements are measured with < 5 mm statistical noise. The long-term ice Velocity is measured with a precision of 1 ma−1. The inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0.47 ± 0.01 km3. The hinge line is mapped with a precision of 20-80 m.

Combining the interferometric ice velocities with ice thickness data, the glacier ice discharge is calculated at and below the hinge line. At the hinge line, the ice flux is 12.1 ± 1 km3 a−1. At the ice front, calf-ice production is only 0.59 km3−1 a−1, meaning that 95% of the ice that crosses the grounding line melts before it reaches the calving front. Assuming steady-state conditions, the melt rate of the glacier tongue averages 12 ± 1 m a−1, with peak values exceeding 20 ma−1 near the hinge line. This high melt rate cannot be accommodated by surface ablation alone (only about 23 ma−1) and is attributed to pronounced basal melting of the ice tongue. Basal melting, often assumed to be negligible in Greenland, is the dominant process of mass release from the floating section of Petermann Gletscher.

Large-scale melting phenomena such as meltwater drainage channels and meltwater accumulation basins of frozen lakes were surveyed on the land ice mass in Jutulgryta, Dronning Maud Land, Antarctica, during the Norwegian Antarctic Research Expedition in 1989–90 (NARE 1989–90). The largest frozen lake that was observed was close to 1 km in width. These melting features were also detected in a Landsat Thematic Mapper image recorded on 12 February 1990. Then, during NARE 1993–94, a 5year glaciological programme was started in this area. In spite of negative air temperatures and the presence of a frozen ice surface, sub-surface melting and runoff were found within the uppermost metre in blue-ice fields. The sub-surface melting is a consequence of solar radiative penetration and absorption within the ice, i.e. the “solid-state-greenhouse effect”. Temperatures in blue ice were about 6°C higher than for snow. Internal melt and meltwater transport were observed throughout the 1 month of measurements. The conditions for active melting in Jutulgryta are probably marginal. A slight increase of air temperatures can result in more “classical” surface melting, whereas a cooling may disable sub-surface melting. Studies of how the extent and characteristics of the melting features change with time can be particularly valuable as indicators of climate change. This ongoing programme clearly identifies the importance of analyzing how these melting features originate, of mapping their present areal distribution, of determining how sensitive they are to climate change and of Studying changes in the past and possible changes in the future.

Analytical and numerical techniques are used to examine the flow response of a sloped slab of power-law fluid (power n) subjected to basal boundary conditions that vary spatially across the flow direction, as for example near an ice-stream margin with planar basal topography. The primary assumption is that basal shear stress is proportional to the basal speed times a spatially variable slip resistance. The ratio of mean basal speed to the speed originating from shearing through the thickness. denoted as r, gives a measure of how slippery the bed is. The principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow. In units of ice thickness H, the spatial scale of spreading is proportional to a single dimensionless number Rn ≡ (r/n+ 1)1/n+1 derived from n and r. The consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to Rn. For an ice stream caused by a band of low slip resistance with a half-width of w H, the margins influence velocity and stress in the central part of the band depending on Rn in comparison to w. Three regimes can be identified, which for n = 3 are quantified as follows: low r defined as R3 < 0.1w, for which the central flow is essentially unaffected by the margins and the driving stress is supported entire by by basal drag; high r defined as R3 > 1w, for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag; intermediate r, for which the driving stress in the center is supported by a combination of basal and side drag. Shear zones that are narrower than predicted on the basis of this theory (≈ R3) would require localized softening of the ice to explain the concentration of deformation at a shorter scale.

Evidence of changing basal and internal ice properties near the grounding line was derived from airborne radio-echo-sounder observations of the ice sheet around the Sør Rondane Mountains, Antarctica. From the trailing figure of the bottom-echo signal, the roughness of the ice bottom near the grounding line was inferred. Results show that the specular components of scattering begin to appear on the ice-shelf side of the grounding line. Furthermore, double-trip echoes were observed with a strong scattering in the shelf area, and their boundary of occurrence was very close to the grounding line. This is evidence of interaction between ice and sea water at the bottom of the ice shelf. We also examined the occurrence of internal layered echoes. In most of the area around the mountains, internal echoes were observed continously, but they were not found at or close to the ice shelf. The boundary between the appearance and disappearance of internal-layer echoes is distinct, and occurs 20–30 km inland from the grounding line. These results suggest that some major change may occur in the internal ice on the inland side of the grounding line.

Interferometric radar observations of Glaciar San Rafael, Chile, were collected in October 1994 by NASA’s Spaceborne Imaging Radar C (SIR-C) at both L- (24 cm) and C-band frequency (5.6 cm), with vertical transmit and receive polarization. The C-band data did not yield good geophysical products, because the temporal coherence of the signal was significantly reduced alter 24 h. The L-band data were, however, successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height, and measure ice velocity with a precision of 4 mm d−1 or 1.4 m a−1. The corresponding error in strain rates is 0.05 a −1 at a 30 m horizontal spacing. The one-dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature-tracking results near the calving front. The results provide a comprehensive view of the ice-flow dynamics of Glaciar San Rafael. The glacier has a core of rapid flow, 4.5 km in width and 3.5° in average slope, surrounded by slower-moving ice, not by rock. Ice velocity is 2.6 m d−1 or 0.95 km a−1 near the equilibrium-line altitude (1200 m), increasing rapidly before the glacier enters the narrower terminal valley, to reach 17.5 md−1 or 6.4 k ma−1 at the calving front. Strain rates are dominated by lateral shearing at the glacier margins (0.4–0.7 a−1), except for the terminal-valley section, where longitudinal strain rates average close to 1 a−1. This spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers.

We present new interpretations of deglaciation in McMurdo Sound and the western Ross Sea, with observationally based reconstructions of interactions between East and West Antarctic ice at the last glacial maximum (LGM), 16000, 12000, 8000 and 4000 BP. At the LGM, East Antarctic ice from Mulock Glacier split; one branch turned westward south of Ross Island but the other branch rounded Ross Island before flowing southwest into McMurdo Sound. This flow regime, constrained by an ice saddle north of Ross Island, is consistent with the reconstruction of Stuiver and others (1981a). After the LGM, grounding-line retreat was most rapid in areas with greatest water depth, especially along the Victoria Land coast. By 12000 BP, the ice-now regime in McMurdo Sound changed to through-flowing Mulock Glacier ice, with lesser contributions from Koettlitz, Blue and Ferrar Glaciers, because the former ice saddle north of Ross Island was replaced by a dome. The modern flew regime was established ∼4000 BP. Ice derived from high elevations on the Polar Plateau but now stranded on the McMurdo Ice Shelf, and the pattern of the Transantarctic Mountains erratics support our reconstructions of Mulock Glacier ice rounding Minna Bluff but with all ice from Skelton Glacier ablating south of the bluff. They are inconsistent with Drewry’s (1979) LGM reconstruction that includes Skelton Glacier ice in the McMurdo-Sound through-flow. Drewry’s (1979) model closely approximates our results for 12000-4000 BP. Ice-sheet modeling holds promise for determining whether deglaciation proceeded by grounding-line retreat of an ice sheet that was largely stagnant, because it never approached equilibrium flowline profiles after the Ross Ice Shelf grounded, or of a dynamic ice sheet with flowline profiles kept low by active ice streams that extended northward from present-day outlet glaciers after the Ross Ice Shelf grounded.

Measurements of temperature in snow along a vertical profile during the onset of spring melting are used to calculate spatial and temporal temperature gradients and terms of the conduction equation with an internal energy-production term are calculated. Heat-transfer information is combined with stratigraphic observations made during melting and allow detailed determination of the timing and location of heterogeneous water movement and of refreezing. Internal energy production is interpreted as latent heat of refreezing of percolated meltwater. Times and locations of flow and refreezing of meltwater are calculated and compared to Stratigraphic observations of layering and changes in density and liquid-water content. Sequences of melt, piping, layering and refreezing seen in calculations and in stratigraphy demonstrate retarded flow at fine-to-coarse transitions, flow along such transitions and refreezing at the transitions to form ice layers. Downslope flow is also observed in the absence of an impermeable horizon to redirect flow from the vertical.

Antarctic subglacial lakes provide аn important boundary condition for thermal analysis of the ice sheet in that the basal ice temperature over lakes may be assumed to be at the pressure-melting point. We have used a one-dimensional vertical heat-transfer equation to determine theoretical temperature values for the ice-sheet base above 77 subglacial lakes identified from airborne radio-echo-sounding data covering 50% of Antarctica. Variations in our temperature results to below the pressure-melting temperature over lakes are due to either our estimate of the geothermal heat flux or a neglect of heat derived from (a) internal ice deformation and (b) basal sliding, in the thermal model. Our results indicate that, when the geothermal heat flux is set at 54 m W m−2, the ice-sheet base above 70% of the known Antarctic subglacial lakes is calculated to be at the pressure-melting value. These lakes are located mainly around Dome C, Ridge B and Vostok station. For the ice sheet above subglacial lakes located hundreds of kilometres from the ice divide, using the same thermal model, loss of heat due to vertical advection is calculated to be relatively high. In such regions, if the ice-sheet base is at the pressure-melting point, heat lost due to vertical advection must be supplemented by heat from other sources. For the three lakes beneath Terre Adélie and George V Land, for instance, the basal thermal gradient calculated to produce pressure melting at the ice-sheet base is equivalent to 1.5–2 times the value obtained when 54 m W m−2 of geothermal heat is used as the sole basal thermal component. We suggest that, as distance from the ice divide increases, so too does the amount of heat due to internal ice deformation and basal sliding. Moreover, by considering the ice-sheet basal thermal characteristics above subglacial lakes which lie on the same ice flowline, we demonstrate empirically that the heat due to these horizontal ice-motion terms varies pseudo-exponentially with distance from the ice divide. The location along a flowline where a rapid increase in the basal heat gradient is calculated may correspond to the onset of large-scale basal sliding.

Black Rapids Glacier, a surge-type glacier in the Alaska Range, most recently surged in 1936–37 and is currently in its quiescent phase. Mass balance, ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994. The annual speed has undergone cyclical fluctuations of as much as 45% about the mean speed. Ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation, which indicates that they are being drinven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from that of Variegated Glacier, another well-studied surge-type glacier in Alaska. The present medial-moraine configuration of Black Rapids Glacier indicates that a surge could occur at any time. However, ice velocity data indicate that the next surge may not be imminent. We belive that there is little chance that the next surge will cross and dam the Delta River.

The stability of a tidewater terminus is controlled by glacial dynamics, calving processes and sedimentary processes at the grounding line. An investigation of grounding-line sediment dynamics and morainal-bank sediment budgets in Glacier Bay, Alaska, U.S.A., has yielded data that enable us to determine the debris fluxes of Grand pacific, Margerie and Muir Glaciers. Debris flux ranges from 105 to 106 m3 a−1, one to two orders of magnitude lower than the glacifluvial sediment fluxes (106−107 m3 a−1). Combined, these fluxes represent the highest yields known for glacierized basins. Large debris fluxes reflect the combined effects of rapid glacier flow, driven by the maritime climate of southeast Alaska, and highly erodible bedrock. Englacial-debris distribution is affected by valley width and relief, both of which control the availability of sediment. The number of tributaries controls the distribution and volume of debris in englacial and supraglacial moraines. At the terminus, iceberg-rafting removes up to two orders of magnitude more sediment from the ice-proximal environment than is deposited by melt-out or is dumped during calving events. Rough estimates of the sediment flux by deforming beds suggests that soft-bed deformation may deliver up to an order of magnitude more sediment to the terminus than is released from within the glacier ice.

Glacio-meteorological data obtained during the Greenland Ice Margin Experiment (GIMEX) investigations in West Greenland (the Søndre Strømfjord transect) have been used to test and calibrate energy-balance/mass-balance models for the ice/snow surface. The region is characterised by the development of a wide zone of low surface albedo in the course of the melting season. This zone was simulated in one of the energy-balance models by including the effect of surficial meltwater on albedo. Observed mass-balance and albedo data were used to constrain the models. Although all the models are capable of predicting the transect balance reasonably well, only the model with the meltwater albedo coupling, is able to reproduce the observed albedo pattern and mass-balance profile along the transect. By including the feedback between surficial meltwater and albedo in the model, the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line (in contrast to what is generally found for valley glaciers). A 1 K warming of the air temperature would increase the mean ablation along the transect by 0.5 m w.e.year −1.

Geodetic surveying and ground-based radar profiling were used to determine geometry and surface motion of the ice sheet on the Dyer Plateau, Antarctica, in the vicinity of an ice-core site on a local dome. Vertical strain measurements in the core hole constrain the depth profile of vertical velocity. These geophysical measurements are used to analyze the profiles of density and annual layer thickness measured on the ice core to estimate the current mass balance of the ice column and the past history of accumulation rate. Consideration of horizontal and vertical mass-flow divergence shows that the profiles of density and vertical velocity are not fully consistent with steady state. Mean density of the firn layer appears to be increasing, which leads to the deduction of a small rate of mass increase (≈ 0.02 m a− 1 ice-equivalent thickness). Over the last 200a there has been a gradual increase in accumulation rate from about 0.46 m a− 1 to 0.54 m a− 1 ice-equivalent thickness in recent time.

Reduced amounts of snow in the eight winters from 1986-87 to 1993-94 at Nagaoka, Japan, seem to be due to a winter air-temprature rise. The winter air temprature has shown cyclic varition gradual increase in the past 100years. The linear rate of the temperature rise in the past century was calculated as 1.35°C per 100 years. Both the maximum Snow depth and winter precipitation showed an inversely positive correlation with winter mean air temperature, The square of the statistical correlation coefficient r2 was calculated as 0.321 and 0.107. respectively. Statistically smoothed curves or the maximum snow depth and winter precipitation showed maximum values in 1940, Fluctuations in deviation of the maximum Snow depth showed smaller values than in precipitation. The minimum winter mean air temperature obtained from a 10 year moving average curve was found in 1942, and the deviation fom the climatic mean changed from negative to positive in 1949. The change in sign or the temperature deviation and the increase of the deviation may be attributable to global warming.

Avalanche forecasting for a given region is still a difficult task involving great responsibility. Any tools assisting the expert in the decision-making process are welcome. However, an efficient and successful tool should meet the needs of the forecaster. With this in mind, two models, were developed using a commercially available software: CYBERTEK-COGENSYSTM, a judgment processor for inductive decision-making–a principally data-based expert system. Using weather, snow and snow-cover data as input parameters, the models evaluate for a region the degree of avalanche hazard, the aspect and altitude of the most dangerous slopes. The output result is based on the snow-cover stability. The new models were developed and have been tested in the Davos region (Swiss Alps) for several years. To rate the models, their output is compared to the a posteriori verified hazard. the first model is purely data-based. Compared to other statistical models, the differences are: more input information about the snow cover from snow profiles and Rutschblock tests, the specific method to search for similar situations, the concise output result and the knowledge base that includes the verified degree of avalanche hazard. The performance is about 60%. The second, more-refined model, is both data- and rule-based. It tries to model the decision-making process of a pragmatic expert and has a performance of about 70%, which is comparable to the accuracy of the public warning.

To obtain a better understanding of the compliance of saline ice, we developed a simple conceptual model of a process that presumably takes place in saline ice. Using elastic models, we assessed the role that phase transformations might play when brine is sealed into small cells during crystal growth. Cooling of a sealed brine cell, leading to the precipitation of ice, provides a mechanism for the accumulation of “large” localized stresses. Based on our analysis, this mechanism has the potential to be a significant source for the nucleation of dislocations, and can conceivably make a significant contribution to the greater compliance (softness) of saline ice relative to non-saline ice.

The results of this model are consistent with the observation that laboratory-grown saline crystals sometimes display extensive differences in mechanical behavior that appear to be due to variations in the growth and storage conditions experienced by the crystals.

Radar-sounding data taken at Uvérsbreen glacier, Svalbard, are used to estimate the relative water content of the temperate part of the glacier. The relative change in water content of the temperate part of the glacier. The relative change in water content is estimated from the strength of the backscttered radar energy without knowing the size of the scatterers. The main findings are that the water content is on average changing by a factor of five in the ice, with the exception of some bright spots believed to stem fro larger water moulins. The general trend is also that the water content is increasing with lower altitude. The applied technique may be a useful method for large-scale mapping of the relative water-content variation in temperate and polythermal glaciers.