Rock instability is believed to be causally linked to permafrost degradation, but it is difficult to demonstrate this directly because of the short record of slope failures in high mountains. While abductive scientific reasoning of ‘increasing permafrost-related instability’ based on the short time frame of recorded rockfall events in high mountains is still difficult, our deductive systemic understanding points toward a strong process linkage between permafrost degradation and rock instability. Enhanced technical understanding of coupled thermo-hydro-mechanical processes and systemic geomorphic understanding of rock slope adjustment in space and over (reaction/relaxation) time are required to accurately predict hazards associated with the impact of climate change on permafrost in bedrock. We identify research needs in four major areas and at the interfaces between them: rock temperature measurement and modelling; remote sensing of rock walls; process understanding of rock mass instability; and flow propagation models of rock-ice avalanches. This short communication identifies key interfaces between research directions to gain a better understanding of trajectories of destabilisation in time and space. We propose coordinated systemic research with respect to scale dependent and transient thermal behaviour, coupled thermo-hydro-mechanical understanding, enhanced remote inventorying of rock wall instability and integrated approaches for a better understanding and modelling of mixed avalanches. Copyright © 2012 John Wiley & Sons, Ltd.

Mid-winter wet avalanche cycles in High Arctic Svalbard occurred during January 2010 and March 2011, allowing studies of slush and wet slab avalanche deposits. Both cycles represented extreme events in magnitude and frequency and were caused by the passage of low-pressure atmospheric systems with positive air temperatures, high wind speeds and 100-year record monthly rainfall. Slush avalanches were confined to river-cut gorges, with low starting-zone inclinations, and deposits consisting of flow lobes and levées. Wet slab avalanches were not confined topographically, started anywhere on open mountain slopes and displayed tongue-shaped debris deposits. During both of the two wet avalanche periods analysed, snowpack conditions favoured the release of slush avalanches, as the snowpack consisted of a coarse-grained middle section above a water-impermeable ice layer. Such snowpack conditions are typical for central Svalbard. The resulting slush and wet slab avalanches were extreme in their size and runout distances, crossing frequently used snowmobile tracks at 20 locations and posing a threat to traffic and infrastructure. Four additional potential large-scale slush avalanche periods were identified from analysis of the meteorological record from Longyearbyen (1912–2011). They cluster in the mid to early 1990s, with comparable meteorological conditions to the January 2010 and March 2011 wet avalanche cycles. It is concluded that the frequency and duration of low-pressure weather systems are the dominant controls on wet snow avalanches, and that mean snow season air temperature (October–May) is of little importance. Copyright © 2011 John Wiley & Sons, Ltd.

To assess the role of thermal contraction-crack polygons (sublimation polygons) in modulating sublimation of buried glacier ice in Antarctica, we applied a 2D numerical model using COMSOL Multiphysics that calculates the rate and spatial variability of vapour diffusion through porous media. Specifically, we examined vapour transport through Granite drift, a dry supraglacial till marked with thermal contraction-crack polygons that rests on glacier ice reportedly ≥8-million years in age. The model results show that sublimation varies with drift texture and surface topography. Initially, the rates are highest beneath relatively coarse-grained sand-wedge deposits at polygon margins, creating deep, surface troughs. As troughs approach ~1-m depth, the cooler atmospheric and soil temperatures that arise from solar shielding reduce the rates of ice sublimation to levels below that at polygon centres, preventing runaway ice loss at polygon margins. Including the effects of a salt-cemented horizon at 10 − 15-cm depth (porosity 20%) and a rocky surface pavement (75% ground coverage), our modelled ice loss at polygon centres, for example, is 0.022 mm a⁻¹, an order of magnitude lower than previous estimates (0.14 mm a⁻¹). This finding highlights the importance of including field-based data for drift texture, topography and microclimate variation in modelling ice sublimation. The results also suggest that stable conditions (no ice loss) at polygon centres are possible with either a 1.9°C decrease in mean annual atmospheric temperature or a 12 per cent increase in mean annual relative humidity. These results indicate that the preservation of buried, multi-million-year-old ice is plausible in the coldest and driest regions of Antarctica. Copyright © 2011 John Wiley & Sons, Ltd.

Indices of the rate of Holocene chemical weathering of pyroxene-granulite gneiss and peridotite are estimated from bedrock surfaces deglaciated c. 9700 years ago. A mean surface lowering rate for pyroxene-granulite gneiss of 4.8 ± 1.0 mm ka⁻¹ is estimated from the mean height of upstanding quartz veins, and Schmidt hammer R-values are used to validate the reference-surface method. Microrelief development and crack-widening rates for peridotite are 2.6 ± 1.1 mm ka⁻¹ and 1.8 ± 0.4 mm ka⁻¹, respectively. Well-developed weathering rinds indicate a mean rind development rate for peridotite of 0.6 ± 0.1 mm ka⁻¹. New indices of rock surface weakening (IRW) and the rock surface weakening rate (WR) are defined in relation to Schmidt hammer mean R-values. IRW values from weathered and unweathered surfaces of known age are 38.7 per cent for gneiss and 34.1–59.2 per cent (depending on the texture of the weathered rock surface) for peridotite: corresponding WR values are 2.7 R-units ka⁻¹ and 2.1–3.7 R-units ka⁻¹, respectively. Our methods and results are evaluated, particularly in relation to previous research and other rock types in Scandinavia. The various indices, being affected in different ways by biochemical and biological mechanical weathering and micro-erosion, are regarded as complementary aids in the investigation of both the effects of chemical weathering and its rate. Copyright © 2010 John Wiley & Sons, Ltd.

In Europe, ramparted depressions have traditionally been interpreted as the relict forms of periglacial ground-ice mounds. In many cases, however, such interpretations have been based on limited subsurface evidence. We present detailed sedimentological and geophysical investigations of ramparted depressions from Llanpumsaint, Wales. These data are used to establish internal structure and to evaluate possible mechanisms for landform formation. Borehole and geophysical data have revealed a thick (∼30 m) sequence of glaciolacustrine sediments beneath the study site. The geological context (drainage of a large proglacial lake) would have been conducive to the formation of: (i) permafrost-related ground-ice mounds, at times when exposed frost-susceptible glaciolacustrine sediments were subject to permafrost aggradation; and (ii) craters associated with the in-situ meltout of blocks of glacier ice grounded in the lake during periods of falling water levels. Rampart deformation structures are consistent with both models, but units of sand and gravel within the ramparts favour a hypothesis that these landforms represent the collapsed remains of ground-ice mounds. This study highlights the importance of recognising and evaluating all possible (periglacial and non-periglacial) models for the development of ramparted depressions. We recommend that future studies carefully consider all possible mechanisms of formation, particularly where subsurface information is limited. Copyright © 2011 John Wiley & Sons, Ltd.

A new automated electrical resistivity tomography (A-ERT) system is described that allows continuous measurements of the electrical resistivity distribution in high-mountain or polar terrain. The advantages of continuous resistivity monitoring, as opposed to single measurements at irregular time intervals, are illustrated using the permafrost monitoring station at the Schilthorn, Swiss Alps. Data processing was adjusted to permit automated time-effective handling and quality assessment of the large number of 2D electrical resistivity profiles generated. Results from a one-year dataset show small temporal changes during periods with snow cover, and the largest changes during snowmelt in early summer and during freezing in autumn, which are in phase with changes in either near-surface soil moisture or subsurface temperature. During the snowmelt period, spatially variable infiltration processes were observed, leading to a rapid increase in soil moisture and corresponding decrease in electrical resistivity over a period of a few days. This infiltration led to the onset of active-layer thawing long before the seasonal snow cover vanished. Statistical analyses showed that both spatial and temporal variability over the course of one year are similar, indicating the significance of spatial heterogeneity regarding active-layer dynamics. As a result of its cost-effective ability to monitor freezing and thawing processes even at greater depths, the new A-ERT system can be widely applied in permafrost regions, especially in the context of long-term degradation processes. Copyright © 2011 John Wiley & Sons, Ltd.

Warm permafrost conditions (mean temperatures of −3°C to −0.1°C) were investigated in detail at 13 valley and mountain sites in the sporadic (10–50%) and extensive (50–90%) discontinuous permafrost zones in the southern half of the Yukon (60°N to 64°N), using a combination of ground temperature monitoring, electrical resistivity tomography (ERT), frost table probing and coring. Sites were selected to cover a wide range of substrates, vegetation types and ground ice contents. ERT profiling in the spring imaged both deep seasonal frost and perennially frozen ground. Deep active layers measured by probing at the end of summer were also detectable by ERT. Where ground temperatures indicated that the base of permafrost was at a depth of less than 25 m, vertical transitions in apparent resistivity were more sharply defined in coarse materials than in fine-grained deposits, probably because of differences in unfrozen moisture contents at temperatures just below 0°C. Apparent resistivity values related to excess ice fraction and ground temperatures were similar to those previously obtained in Mongolia and Iceland, but generally lower than in ice-rich rock glaciers in European studies. The observations revealed the complexity of site conditions where permafrost is discontinuous and the utility of ERT, in combination with other methods, to investigate permafrost thickness, spatial extent and ice content for infrastructure planning or climate change studies. Copyright © 2011 John Wiley & Sons, Ltd.

The coupling between air and ground temperatures in the mountains of southern Norway was examined using 12 shallow boreholes drilled in August 2008. Three borehole arrays (at Juvvass, Jetta and Tron), each with boreholes at different elevations, were established along a continentality gradient. At the least continental site (Juvvass), the transect includes boreholes with shallow seasonal frost to continuous permafrost, while at Jetta and Tron, the arrays covered the transition from relatively deep seasonal frost to marginal permafrost. On the north slope of Tron, however, ground surface temperatures indicate more widespread permafrost conditions, apparently due to the negative thermal anomaly associated with an openwork block field. The surface offsets (mean ground surface temperature (MGST) minus mean air temperature (MAT)) ranged from < 1 °C for unvegetated wind-scoured sites to up to 4.5 °C for sites with a thick, prolonged snow cover. Active-layer thicknesses at the borehole sites close to the lower limit of mountain permafrost were up to 10 m in bedrock, even under a low thermal diffusivity sediment cover. The mean ground temperature at 10-m depth differed significantly from the MGST, mainly due to the 3D thermal effects of the varying snow cover. Our air temperature measurements do not support the inference that the observed decrease in the lower elevational limit of mountain permafrost with continentality is mainly due to lower MAT. Rather, the pattern fits with an eastwards decrease in the lower limit of block fields and snowfall amounts. Copyright © 2011 John Wiley & Sons, Ltd.

A ten-year record (1999–2009) of annual mean ground surface temperatures (MGSTs) and mean ground temperatures (MGTs) was analysed for 16 monitoring sites in Jotunheimen and on Dovrefjell, southern Norway. Warming has occurred at sites with cold permafrost, marginal permafrost and deep seasonal frost. Ongoing permafrost degradation is suggested both by direct temperature monitoring and indirect geophysical surveys. An increase in MGT at 6.6–9.0-m depth was observed for most sites, ranging from ~0.015 to ~ 0.095°C a^-1. The greatest rate of temperature increase was for sites having MGTs slightly above 0°C. The lowest rate of increase was for marginal permafrost sites that are affected by latent heat exchange close to 0°C. Increased snow depths and an increase in winter air temperatures appear to be the most important factors controlling warming observed over the ten-year period. Geophysical surveys performed in 1999 to delineate the altitudinal limit of mountain permafrost were repeated in 2009 and 2010 and indicated the degradation of some permafrost over the intervening decade. Copyright © 2011 John Wiley & Sons, Ltd.

Advective heat transported by water percolating into discontinuities in frozen ground can rapidly increase temperatures at depth because it provides a thermal shortcut between the atmosphere and the subsurface. Here, we develop a conceptual model that incorporates the main heat-exchange processes in a rock cleft. Laboratory experiments and numerical simulations based on the model indicate that latent heat release due to initial ice aggradation can rapidly warm cold bedrock and precondition it for later thermal erosion of cleft ice by advected sensible heat. The timing and duration of water percolation both affect the ice-level change if initial aggradation and subsequent erosion are of the same order of magnitude. The surplus advected heat is absorbed by cleft ice loss and runoff from the cleft so that this energy is not directly detectable in ground temperature records. Our findings suggest that thawing-related rockfall is possible even in cold permafrost if meltwater production and flow characteristics change significantly. Advective warming could rapidly affect failure planes beneath large rock masses and failure events could therefore differ greatly from common magnitude reaction-time relations. Copyright © 2011 John Wiley & Sons, Ltd.