We present results of an investigation of two jökulhlaups (glacial lake outburst floods) at Gornergletscher, Switzerland, using dye-tracer experiments and complementary hydrological measurements. Repeated dye injections into moulins showed that tracer transit speeds were larger after the lake had emptied, but when proglacial discharge was still high, than during the main phase of the jökulhlaup. This counter-intuitive finding was modelled by tracer retardation inside the injection moulin. This model, together with an estimate of the maximum time the tracer takes to transit the injection moulin, allows us to calculate bounds on the transit speed in the main drainage channel where the lake water flows. These results indicate that the main drainage channel transit speeds are indeed highest during the peak of the flood. Moreover, it is known from a previous study that water amounting to half of the lake volume is temporarily stored within the glacier during a Gornergletscher jökulhlaup. Our observations suggest that this process occurred via lateral spreading of water at the glacier bed.

Observational data allowing the validation of jökulhlaup models are sparse. We were able to inject dye tracer directly into the drainage channel of a glacial lake during the onset of its outburst. This made it possible to test an established jökulhlaup model, not only against discharge measurements, but for the first time also against water flow speeds inferred from measurements. We drive the jökulhlaup model, based on the Spring–Hutter equations, with measured subglacial water pressure, lake water temperature and lake level. The model is fitted to the measured lake discharge and inferred flow speeds using the initial channel size, the channel roughness and sinuosity. Our calculations show that an ingenuous application of the model, fitting it to the lake discharge only, overestimates water flow speeds. For the second day of the outburst, this can be remedied by fitting the model to the inferred flow speeds as well, requiring that either the heat transfer or the sinuosity of the channel be increased. However, the low inferred flow speeds on the first day of the outburst cannot be fitted with any parameter combination, showing that, initially, the water does not flow through an R channel. Hence, the early stages of this jökulhlaup cannot be simulated by an R-channel model.

The puzzling fact that Jakobshavn Isbræ, West Greenland, is flowing very fast but without any significant seasonal velocity changes, despite big amounts of surface-derived meltwater entering the ice stream (Echelmeyer and Harrison, 1990), has been explained by a combination of different types of measurements. It is now well established from seismic measurements and radio-echo sounding that Jakobshavn Isbræ flows through a deeply eroded subglacial trench that, even 50 km inland of the grounding line, extends as far as 1500 m below sea level (Clarke and Echelmeyer, 1996; Legarsky and Huang, 2006). Temperature measurements in boreholes down to 65% of the 2500 m thick ice stream at site B, some 50 km upstream of the calving front (Fig. 1b; Iken and others, 1993), were used to infer the presence of a substantial layer of temperate ice, the thickness of which was estimated to be at least 300 m by modeling and matching internal layering structures (Funk and others, 1994; Lüthi and others, 2002). The presence of a thick layer of temperate ice under very high driving stress allows for high ice-deformation rates, which contribute substantially to the observed fast flow velocities. Basal motion, while certainly important, seems to be barely influenced by the seasonal meltwater input (Echelmeyer and Harrison, 1990).

Clusters of surge-type glaciers occur in many areas peripheral to the Greenland ice sheet (Weidick, 1988). In East Greenland (68–72° N), 30–70% of glaciers are of surge type, but only five of these have been described (Jiskoot and others, 2003, and references therein). Regional surge characteristics and dynamics have been used to suggest a hydrologically controlled surge mechanism, with surge behaviour that is more Alaskan-type than Svalbard-type in this region (Jiskoot and others, 2001, 2003; Murray and others, 2002, 2003; Pritchard and others, 2005).

Field surveys of supraglacial ponds on debris-covered glaciers in the Nepal Himalaya clarify that ice-cliff calving occurs when the fetch exceeds ∼80 m. Thermal undercutting is important for calving processes in glacial lakes, and subaqueous ice melt rates during the melt and freeze seasons are therefore estimated under simple geomorphologic conditions. In particular, we focus on the differences between valley wind-driven water currents in various fetches during the melt season. Our results demonstrate that the subaqueous ice melt rate exceeds the ice-cliff melt rate when the fetch is >20 m and water temperature is 2–4°C. Calculations suggest the onset of calving due to thermal undercutting is controlled by water currents driven by winds at the surface of the lake, which develop with expanding water surface.

A number of scientists have already warned against the risks of interpreting paleoclimate records without an adequate understanding of the diffusion of relevant chemical traces in deep ice cores (Gow, 1971; Ikeda and others, 1999; Bender, 2002; Faria and others, in press, and references therein). Particularly critical is the formation – either prior to drilling or during ice-core storage – of micro-inclusions such as solid inclusions, microscopic bubbles and plate-like inclusions (PLIs).

The transient response of glaciers to climate variations is investigated with a novel low-order model of an idealized glacier resting on uniformly inclined bedrock. The model consists of two volumes representing the accumulation and ablation areas, which are joined by a flux gate controlling mass flow according to the shallow-ice approximation. Under the assumption of a constant vertical mass-balance gradient, a volume–length scaling relation is derived which depends explicitly on mass-balance gradient and bedrock slope. Analytic expressions for the volume and area timescales are given, which are inversely proportional to the mass-balance gradient and a geometric factor which is the ratio between the vertical extent of the ablation area and the ice thickness at the equilibrium line. From the low-order model, a dynamical system in length and volume is obtained. Results from this system are in good agreement with solutions obtained from a transient finite-element model solving the full force-balance and mass-conservation equations. Under periodic forcing there are significant deviations of the length response, which show that the usual relaxation-type parameterization of length change is not well suited for short-term reactions. Switching on and off periodic climate forcing, the model glaciers show surprisingly large initial and final transient responses that have not been investigated before. These results are of significance for the interpretation of length and thickness changes observed on glaciers.

Dome A is the highest ice feature in Antarctica, at over 4000 m a.s.l., and overlies the Gamburtsev mountains. It is believed that deep ice-core drilling in this area may reveal the oldest ice in Antarctica, providing an unparalleled paleoclimate record in excess of 1 Ma, and perhaps going back as far as 1.2 Ma (Xiao and others, 2008). However, little is known about this area because its height and distance from the coast and scientific stations makes access difficult.

Seismic reflection techniques are a powerful way to probe physical properties of subglacial strata. Inversion of seismic data for physical properties may be hampered, however, by lack of knowledge of the source amplitude as well as lack of knowledge of the compressional and shear attenuation in the ice. New methods are described to measure the source signature that require no a priori knowledge of the ice attenuation profile. Another new method is described to obtain the angular dependence of the subglacial bed reflection coefficient that is relatively insensitive to knowledge of the ice attenuation. Finally, a correction is provided to a long-standing error in the literature regarding measurement of the bed normal incidence reflection coefficient.

Analysis of sediment-laden ice accreted at the base of ice sheets provides useful information on subglacial conditions and processes that otherwise cannot be observed or are very difficult to observe. While sediment-laden accreted basal ice can be accessed directly at the terminus of alpine glaciers, the basal zone of ice sheets is only accessible by drilling. Small amounts of sediment in the ice have provided few or no problems for conventional ice-core drilling (Gow and others, 1979; Weis and others, 1997); however, the higher-sediment-content accreted ice beneath West Antarctic ice streams (Vogel and others, 2005) has not been recovered using the California Institute of Technology (Caltech) hot-water ice corer (Engelhardt and others, 2000).