It is well known that ice-cube spikes form by the extrusion of water at the surface of a freezing ice cube, driven by the expansion accompanying freezing. The growing spikes are water-filled ice tubes, growing at their tips as the water is expelled. This paper represents an exploration of their formation and the principles behind whether a freezing ice cube grows a spike or not. For this purpose, ice cubes are frozen in one set of conditions to observe what happens when spikes do or do not form. Spike formation requires a nearly steady-state freezing-and-extrusion process at the growing tip, in order to maintain a nearly constant diameter. Most spikes are polycrystals with special orientation relationships that evidently allow the steady state to become established. Thus the orientations of the initial crystals, formed by chance, help to determine whether a spike forms or not. The main alternative to spike formation is flooding over the upper surface of the ice. Spike formation depends upon an effectively non-zero contact angle of water on ice that impedes flooding. The onset of flooding is probably sensitive to the ice growth rate at the water surface, which depends strongly upon the crystal orientation with respect to the water surface where it contacts the crystal.

Arches in stratigraphic layers directly under a flow divide (Raymond bumps) are predicted by models of steady ice-sheet flow, and have been observed in several ice domes. Here, we model the evolution of these layers when a formerly stationary divide migrates rapidly to a new position, then again becomes stationary, leaving the arched layers in a flank position. As they are then carried downstream with the flow, these abandoned arches can develop into recumbent folds. These folds can occur over a wide range of divide migration speeds. The shearing flow that produces these recumbent folds also distributes the folded layers over a wide distance downstream from the original divide location. If the divide offset is abrupt, ‘pre-cores’, or material lines comprising core-relative isochrones, can be used to quickly identify portions of an abandoned Raymond bump that would be overturned at any future ice-core site downstream. If, as appears to be the case in Greenland, the divide is never stable long enough to produce a mature arch, folds of this type would not occur. The most likely place to find such folds might be the flank of an ice ridge bounded by unsteady ice streams.

The effects of silt-sized particles (average diameter of 50 μm) on the compressive creep of polycrystalline ice have been studied at stress levels from 0.1 to 1.45 MPa and temperatures of –12ºC and –10°C. Dislocation densities during creep have been estimated using a dislocation-based model of anelasticity. The results indicate that at low concentrations (up to 4wt.%), particles increase the minimum creep rate. Power-law behavior with an exponent of 3 was observed for both particle-free ice and ice with 1 wt.% particles when the stress was >0.3 MPa. In contrast, linear behavior was observed when the stress was <0.3 MPa. Calculations show that the linear behavior is associated with a constant dislocation density, and the power-law behavior is associated with increasing dislocation densities with increasing stress.

The surface velocity field of Devon Ice Cap, Nunavut, Canada, was mapped using interferometric synthetic aperture radar (InSAR). Ascending European Remote-sensing Satellite 1 and 2 (ERS-1/-2) tandem mode data were used for the western and southeast sectors, and 3 day repeat pass ERS-1 imagery for the northeast sector. Speckle-tracking procedures were used with RADARSAT 1 imagery to obtain surface velocities over the terminus of Belcher Glacier (a major calving front) where decorrelation between ERS data occurred. The InSAR data highlight a significant contrast in ice-flow dynamics between the east and west sides of the ice cap. Ice movement west of the main north–south divide is dominated by relatively uniform ‘sheet’ flow, but three fast-flowing outlet glaciers that extend 14–23km beyond the ice-cap margin also drain this region. Several outlet glaciers that extend up to 60 km inland from the eastern margin drain the eastern side of the ice cap. The dominant ice-flow regimes were classified based on the relationship between the driving stress (averaged over a length scale of ten ice thicknesses) and the ratio of surface velocity to ice thickness. The mapped distribution of flow regimes appears to depict the spatial extent of basal sliding across the ice cap. This is supported by a close relationship between the occurrence of flow stripes on the ice surface and flow regimes where basal sliding was found to be an important component of the glacier motion. Iceberg calving rates were computed using measured surface velocities and ice thicknesses derived from airborne radio-echo sounding. The volume of ice calved between 1960 and 1999 was estimated to be 20.5 ± 4.7 km3 (or 0.57 km3 a–1). Approximately 89% of this loss occurred along the eastern margin. The largest single source is Belcher Glacier, which accounts for ~50% of the total amount of ice calved.

We have determined the in situ electric field attenuation length Lα (defined as the length over which the signal amplitude diminishes by a factor 1/e) for radio-frequency signals broadcast vertically through South Polar ice and reflected off the underlying bed. Conservatively assuming a bedrock field reflectivity for f = 380 MHz, and T = –50°C; the errors incorporate uncertainties in R. This value is consistent with previous estimates that the radiofrequency attenuation length exceeds the attenuation length at optical frequencies by an order of magnitude.

We report measurements of ice surface elevation, ice thickness and surface area for Glaciar Tyndall, Patagonia, made in 1999–2002. The measurements, together with previously published observations, show acceleration over the last few decades of the rates of thinning and retreat of the main calving front. The acceleration of shrinkage appears to be driven by a combination of climate and feedback processes, the dominant feedback being increased melting associated with lowering of the glacier surface (elevation feedback). The melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat. The glacier bed has low slope and remains below the elevation of the lake spillway for >14 km upstream from the 2000 calving front, indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges.

The late-Holocene trends in δ18O differ significantly in two ice cores (30 km apart) from the area of Taylor Dome, Antarctica. It is unlikely that the trend in the core from Taylor Mouth (the flank site) is due to a standard δ18O–surface temperature relationship. Assuming that the Taylor Dome (nearsummit) core records local climate variations common to both cores, we assess two leading possible causes for the observed differences: (1) Relative to Taylor Dome, Taylor Mouth may collect snow from more sources with distinct isotopic compositions. (2) Vapor motion during prolonged near-surface exposure may cause post-depositional isotope enrichment at Taylor Mouth, where the accumulation rate is low. Our model of firn pore-space vapor and sublimating ice grains suggests that post-depositional processes can modify δ18O values by several ‰. Isotopic samples from areas with significantly different accumulation rates near Taylor Mouth could differentiate between possibilities (1) and (2).

A 14 year kinematic survey of Spruce Creek rock glacier, Colorado, USA, provides information on rates and controls of surface strain. Steel-tape measurements of differential movement yield data of cm-scale accuracy, sufficient to assess strain patterns over small portions of the very slowly deforming rock glacier. Flow rates are typically <10cma–1, and measured strain rates range from 1.0 × 10–5a–1 to 1.5 × 10–3a–1. The primary control on longitudinal strain is changing surface slope, with extending flow occurring in areas of down-valley increase in slope, and compressing flow in areas of down-valley slope decrease. Relatively high strain rates are associated with higher flow velocities and with the impingement of faster-flowing up-valley portions of the rock glacier on the slower-moving lower portion. Overall strain rates decreased through the study period, probably as a result of a slowing of the upper part of the rock glacier. Transverse ridges are associated with longitudinal shortening, caused by either slope changes or impingement of faster-moving sections of the rock glacier on slower-moving sections, but transverse ridges do not occur in every area of strong longitudinal shortening.

Slug testing allows estimation of subglacial hydraulic properties by evaluating the response of a coupled borehole–subglacial flow system to an artificial displacement of its steady-state hydraulic head. However, existing models developed specifically for application to slug-test data collected in glacier boreholes are challenging to apply in practice. Here, we demonstrate that conventional linear methods, which are relatively readily applicable and widely used in groundwater studies, can also be used to estimate subglacial hydraulic properties. Overdamped, underdamped and critically damped slug-test data were recorded in fluctuating boreholes drilled to the bed of Haut Glacier d’Arolla, Valais, Switzerland. We find that non-linear effects in the data are negligible, supporting the application of conventional hydrogeological methods. Results suggest that the hydraulic conductivity of the unconsolidated sediments within the area influenced by a major subglacial drainage channel is enhanced (several 10–2 m s–1; typical of gravelly sand) compared to areas outside the zone of influence (~0.1 × 10–2ms–1; typical of silty sand). A distance to a flow boundary within the subglacial aquifer, inferred on the basis of slug-test analysis, was found to coincide with the actual location of the subglacial channel. Sensitivity analyses reveal that uncertainties in borehole and filter radii, as well as the storage coefficient of the subglacial aquifer, are more likely to affect the accuracy of the hydraulic and distance estimates than uncertainties regarding the repeatability of the slug-test responses and curve-fitting procedures involved in the conventional hydrogeological methods.

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.

Comparison of numerically computed solutions to exact (analytical) time-dependent solutions, when possible, is superior to intercomparison as a technique for verification of numerical models. At least two sources of such exact solutions exist for the isothermal shallow ice-sheet equation: similarity solutions and solutions with ‘compensatory accumulation’. In this paper, we derive new similarity solutions with non-zero accumulation. We also derive exact solutions with (i) sinusoidal-in-time accumulation and (ii) basal sliding. A specific test suite based on these solutions is proposed and used to verify a standard explicit finite-difference method. This numerical scheme is shown to reliably track the position of a moving margin while being characterized by relatively large thickness errors near the margin. The difficulty of approximating the margin essentially explains the rate of global convergence of the numerical method. A transformed version of the ice-sheet equation eliminates the singularity of the margin shape and greatly accelerates the convergence. We also use an exact solution to verify an often-used numerical approximation for basal sliding and we discuss improvements of existing benchmarks.

Surface melting rarely occurs across most of the Antarctic ice sheet, away from the warmer coastal regions. Nonetheless, isolated melt features are preserved in the firn and ice in response to infrequent and short-lived melting events. An understanding of the formation and occurrence of these melt layers will help us to interpret records of past melt occurrences from polar ice cores such as the Siple Dome ice-core record from West Antarctica. A search in the near-surface firn in West Antarctica found that melt features are extremely rare, and consist of horizontal, laterally continuous, one to a few millimeter thick, ice layers with few air bubbles. The melt layers found date from the 1992/93 and 1991/92 summers. Field experiments to investigate changes in stratigraphy taking place during melt events reproduced melt features as seen in the natural stratigraphy. Melting conditions of varying intensity were created by passively heating the near-surface air for varying lengths of time inside a clear plastic hotbox. Melt layers formed due entirely to preferential flow and subsequent refreezing of meltwater from the surface into near-surface, fine-grained, crust layers. Continuous melt layers were formed experimentally when positive-degree-day values exceeded 1ºC-day, a value corresponding well with air-temperature records from automatic weather station sites where melt layers formed in the recent past.

Glacier mass changes are considered to represent key variables related to climate variability. We have reconstructed a proxy for annual mass-balance changes in Grosse Aletschgletscher, Swiss Alps, back to AD 1500 using a non-linear back-propagation neural network (BPN). The model skill of the BPN performs better than reconstructions using conventional stepwise multiple linear regression. The BPN, driven by monthly instrumental series of local temperature and precipitation, provides a proxy for 20th-century mass balance. The long-term mass-balance reconstruction back to 1500 is based on a multi-proxy approach of seasonally resolved temperature and precipitation reconstructions (mean over a specific area) as input variables. The relation between the driving factors (temperature, precipitation) used and the reconstructed mass-balance series is discussed. Mass changes in Grosse Aletschgletscher are shown to be mainly influenced by summer (June–August) temperatures, but winter (December–February) precipitation also seems to contribute. Furthermore, we found a significant non-linear part within the climate–mass-balance relation of Grosse Aletschgletscher.

Synchrotron-based micro-X-ray fluorescence (μXRF) equipment has been used to analyze impurities in polar ice. A customized sample holder has been developed and the μXRF equipment has been adapted with a thermal control system to keep samples unaltered during analyses. Artificial ice samples prepared from ultra-pure water were analyzed to investigate possible contamination and/or experimental artefacts. Analyses of polar ice from Antarctica (Dome C and Vostok) confirm this μXRF technique is non-destructive and sensitive. Experiments can be reproduced to confirm or refine results by focusing on interesting spots such as crystal grain boundaries or specific inclusions. Integration times and resolution can be adjusted to optimize sensitivity. Investigation of unstable particles is possible due to the short analysis time. In addition to identification of elements in impurities, μXRF is able to determine their speciations. The accuracy and reliability of the results confirm the potential of this technique for research in glaciology.