This paper presents a simple model to estimate ice ablation under a thick supraglacial debris cover. The key method employed in the model is to establish a link between the debris heat flux and the debris temperature at a certain depth when the heat transfer in the debris is described by a diffusion process. Given surface temperature, debris thermal properties and relevant boundary conditions, the proposed model can estimate mean debris temperature at interfaces of different debris layers using an iterative procedure, and then the heat flux for ice ablation. The advantage of the proposed model is that it only requires a few parameters to conduct the modeling, which is simpler and more applicable than others. The case study on Koxkar glacier, west Tien Shan, China, shows, in general, that the proposed model gives good results for the prediction of debris temperatures, except for an apparent phase shift between modeled and observed values. We suggest that this error is mainly due to complex phase relations between debris temperature and debris heat flux. The modeled ablation rates at three experimental sites also show good results, using a direct comparison with observed data and an indirect comparison with a commonly used energy-balance model.

A series of satellite images of Mýrdalsjökull, Iceland, was analyzed in view of their value for mass-balance investigations. A combination of optical satellite images from the ASTER sensor and synthetic aperture radar data from ERS-2 and Envisat ASAR proved very useful. The glacier margin of Mýrdalsjökull was delineated on ASTER images from summer and winter 2004. With a time series of summer ASAR images it was possible to monitor the temporal and spatial development of the transient snowline (TSL) throughout the year 2004, as well as the firn line (FL) at the end of the balance year. An ‘inverse’ function was applied to visually enhance detail in the radar imagery. Winter radar images were not useful for mass-balance observations because of frequent surface melting, which prevented the transparency of the snow cover for C-band microwaves. Interannual mass-balance fluctuations were observed by comparing three radar images acquired in late summer 1998, 1999 and 2004 respectively. These fluctuations follow the same trend as the annual mean air temperature which shows a strong increasing trend between 1999 and 2004. An accumulation-area ratio of <0.43 was determined for 2004, indicating clear negative mass-balance conditions. Monitoring the TSL-FL with radar summer images for mass-balance studies, rather than the equilibrium line (EL), is suggested for large ice caps in maritime climates.

We present a model study investigating the summer evolution of supraglacial lakes on the Greenland ice margin. Using a one-dimensional (1-D) model we calculate the surface ablation for a bare ice surface and beneath supraglacial lakes for 30 days in the summers of 1999 and 2001. The surface ablation beneath the lake was enhanced by 110% in 1999 and 170% in 2001 compared with the ablation for bare ice. We then use the results from the 1-D model to further model the vertical and horizontal evolution of the supraglacial lakes, the results of which are compared with satellite images. Within the region of the ice sheet where supraglacial lakes presently occur, the area covered by supraglacial lakes is found to be more or less independent of the summer melt rate but controlled by topography. We therefore predict that, inside this region, the area covered by supraglacial lakes will remain constant even in a warmer climate. However, in a warmer climate, surface melting will occur higher on the ice sheet where small surface slopes favour formation of large supraglacial lakes. Enhanced surface melting beneath such lakes is a hitherto overlooked feedback mechanism related to climate warming.

Using Geographical Information System (GIS) and remote-sensing technologies, we describe quantitative measurements of glacier variations in the Geladandong mountain region of central Tibet. Data from Landsat images at three different times, 1973–76, 1992 and 2002, are compared with glacier areas digitized from a topographic map based on aerial photographs taken in 1969. We find that while some glaciers have advanced during the past 30 years, others have retreated. The area of retreat is much larger than that of advance. The total glacier area has decreased from 889km2 in 1969 to 847km2 in 2002, a reduction of almost 43 km2 (i.e. 4.8% decrease, or an average of 1.29km2 a–1). The variation of glacier area in the Geladandong mountain region is not as large as in other regions within the Tibetan Plateau. Glacier areas decreased 4.7km2 (i.e. an average of 0.68km2 a–1) during 1969–76, 15.4km2 (0.96km2 a–1) during 1976–92, and 22.4km2 (2.24km2 a–1) during 1992–2002, suggesting accelerated glacier retreat in recent years. The recession rates of glacier termini also increased. It is likely that the increase in summer air temperature is the major reason for glacier shrinkage in the Geladandong mountain region.

Radio-echo sounding data are used to investigate bed roughness beneath the three enhanced-flow tributaries of Slessor Glacier, East Antarctica. Slow-moving inter-tributary areas are found to have rough beds, while the bed of the northernmost tributary is relatively smooth. A reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary, and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times, so marine sediments may have accumulated here. Together, these factors are further support for the dominance of basal motion in this tributary, reported elsewhere. Conversely, although the other two Slessor tributaries may have water routed beneath them, they would not have been below sea level before the growth of the ice sheet, so cannot be underlain by marine sediments. They are also found to be rough, and, within the range of uncertainties, it is likely that basal motion does not play a major role in the flow of these tributaries. Perhaps the most interesting area, however, is a deep trough where flow rates are currently low but the bed is as smooth as the northern Slessor trough. It is proposed that, although ice deformation currently dominates in this trough, basal motion may have occurred in the past, when the ice was thicker.

Wind tunnel measurements of snowdrift in a turbulent, logarithmic velocity boundary layer have been made in Davos, Switzerland, using natural snow. Regression analysis gives the drift threshold friction velocity (u*t), assuming an exponential drift profile and a simple drift to friction velocity relationship. Measurements over 15 snow covers show that u*t is influenced more by snow density and particle size than by ambient temperature and humidity, and varies from 0.27 to 0.69 ms–1. Schmidt’s threshold algorithm and a modified version used in SNOWPACK (a snow-cover model) agree well with observations if small bond sizes are assumed. Using particle hydraulic diameters, obtained from image processing, Bagnold’s threshold parameter is 0.18. Roughness lengths (z0) vary between snow covers but are constant until the start of drift. Threshold roughness lengths are proportional to . The influence of macroscopic objects on the roughness length is shown by the lower values measured over the smooth and flat snow surface of the wind tunnel (0.04 ≤ z0 ≤ 0.13 mm), compared to field measurements. Mean drifting-snow grain sizes for mainly new and partly decomposed snow are 100–175 μm, and independent of surface particle size.

We have made side-by-side measurements in several boreholes at Summit, Greenland, using borehole optical stratigraphy (BOS) and neutron-scattering density logging techniques. The BOS logs show strong positive correlation at shallow depths with neutron-scattering logs taken in the same borehole. This supports the hypothesis that BOS detects changes in density. The positive correlation between returned brightness and density decreases with depth and finally becomes negative. We conclude this inversion of correlation is related to changes in densification regime from grain-boundary sliding to pressure sintering.

A sedimentary sequence of till overlying a gravel aquifer was instrumented with water-pressure transducers prior to a small, anticipated surge of the margin of the glacier Breiðamerkurjökull in Iceland. The records of water pressure at each transducer site show a well-defined temporal sequence of hydraulic regimes that reflect the changing recharge of surface-derived meltwater, the pressure drop along the drainage pathway and the pattern of ice loading. The poroelastic and water-pressure response of glacially overridden sediments to the recharge rate is determined in the frequency domain through an analytic solution. This permits the in situ conductivity, compressibility and consolidation states of subglacial sediments to be derived, and reveals aquifer-scale compressibility that produces an important water-pressure wave associated with the advancing glacier. The model is then used to explore how varying conductivity/compressibility, largely determined by granulometry, can determine drainage states and instabilities that may have a large impact on glacier/ice-sheet dynamics, and how the drainage time of surface water to the bed can determine the frequency response of subglacial groundwater regimes and their influence on subglacial sediment stability. Mismatches between model predictions and specific events in water-pressure records are used to infer processes that are not incorporated in the model: hydrofracturing that changes the hydraulic properties of subglacial sediments; the impact on groundwater pressure of subglacial channel formation; upwelling beyond the glacier margin; and rapid variations in the state of consolidation. The poroelastic model also suggests how seismic methods can be developed further to monitor hydraulic conditions at the base of an ice sheet or glacier.

Automatic c-axes analyzers have been developed over the past few years, leading to a large improvement in the data available for analysis of ice crystal texture. Such an increase in the quality and quantity of data allows for stricter statistical estimates. The current textural parameters, i.e. fabric (crystallographic orientations) and microstructure (grain-boundary networks), are presented. These parameters define the state of the polycrystal and give information about the deformation undergone by the ice. To reflect the findings from automatic measurements, some parameter definitions are updated and new parameters are proposed. Moreover, a MATLAB® toolbox has been developed to extract all the textural parameters. This toolbox, which can be downloaded online, is briefly described.

Despite their relatively small total ice volume, mid-latitude valley glaciers are expected to make a significant contribution to global sea-level rise over the next century due to the sensitivity of their mass-balance systems to small changes in climate. Here we use a degree-day model to reconstruct the past century of mass-balance variation at ‘Ka Roimata o Hine Hukatere’ Franz Josef Glacier, New Zealand, and to predict how mass balance may change over the next century. Analysis of the relationship between temperature, precipitation and mass balance indicates that temperature is a stronger control than precipitation on the mass balance of Franz Josef Glacier. The glacier’s mass balance, relative to its 1986 geometry, has decreased at a mean annual rate of 0.02m a–1 w.e. between 1894 and 2005. We compare this reduction to observations of terminus advance and retreat, of which Franz Josef Glacier has the best record in the Southern Hemisphere. For the years 2000–05 the relative mass balance ranged from –0.75 to +1.50m a–1 w.e., with 2000/01 the only year showing a negative mass balance. In a regionally downscaled Intergovernmental Panel on Climate Change mean warming scenario, the annual relative mass balance will continue to decrease at 0.02m a–1 w.e. through the next century.

The specific surface area (SSA) is considered an essential microstructural parameter for the characterization of snow. Photography in the near-infrared (NIR) spectrum is sensitive to the SSA. We calculated the snow reflectance from calibrated NIR images of snow-pit walls and measured the SSA of samples obtained at the same locations. This new method is used to map the snow stratigraphy. The correlation between reflectance and SSA was found to be 90%. Calibrated NIR photography allows quantitative determination of SSA and its spatial variation in a snow profile in two dimensions within an uncertainty of 15%. In an image covering 0.5–1.0 m2, even layers of 1mm thickness can be documented and measured. Spatial maps of SSA are an important tool in initializing and validating physical and chemical models of the snowpack.

The fabric of polycrystalline ice is typically described using the c-axis orientation alone, but this is insufficient for a full description of grain orientations in this hexagonal material. Electron backscatter diffraction (EBSD) provides full c- and a-axis orientation of individual grains, and is used here to study Greenland Ice Sheet Project 2 (GISP2) ice specimens from depths of 1551, 1642 and 1745 m. Complete orientation data are used to compare nearest-neighbor relationships to overall fabric and to differentiate between recrystallization mechanisms. Changes in orientation between grains and subgrains in GISP2 specimens were correlated with the appearance of grain boundaries on thin sections and used to identify grain sets that were probably produced by polygonization. Comparison of grain misorientations that take into account both c- and a-axis differences with those derived from c-axis directions alone reveals the presence of polygonization and illustrates the usefulness of this technique.

A fundamental problem in avalanche science is understanding the interaction between frictional processes taking place at the basal running surface and dissipative mechanisms within the avalanche body. In this paper, we address this question by studying how kinetic energy is dissipated into heat in snow avalanches. In doing so we consider the effect of random granular fluctuations and collisions in depth-averaged snow avalanche models. We show that relationships between the size of the granular fluctuations and the energy dissipated by granular collisions can be obtained by studying the energy input required to maintain steady-state flows. The energy input for granular fluctuations comes from mechanisms operating in the basal layer. The kinetic energy of the flow at the basal layer is converted to granular agitation energy, a random kinetic energy, which in turn is dissipated as heat by both viscous shearing and inelastic collisions at higher levels in the avalanche profile. Thus granular fluctuations play a crucial role in understanding the total dissipation process. We apply our theoretical considerations to develop a constitutive model for dense snow avalanches and are able to accurately model steady-state velocity profiles of both snow-chute experiments and field measurements.

We present an overview and the first systematic results on the backscatter properties of snow samples with different grain properties. During a 2 year study we investigated the effect of the apparent characteristics of the samples on the intensity enhancement in the direction of exact backscatter (retroreflection), using a specific instrument designed for backscatter measurements. We observed that a sharp peak in intensity (the hot spot) occurs for most types of snow, which is not observable with traditional goniometers. The key factors in the peak properties are the temperature (related to the changes in grain structure) and grain shape and size. These results form the basis of a larger backscatter data archive which is being applied in the systematic study and exploitation of ‘hot spots’ in remote sensing of natural targets, as well as in the development of airborne laser intensity measurement.