Permafrost and related thermo-hydro-mechanical processes are thought to influence high alpine rock wall stability, but a lack of field measurements means that the characteristics and processes of rock wall permafrost are poorly understood. To help remedy this situation, in 2005 work began to install a monitoring system at the Aiguille du Midi (3842 m a.s.l). This paper presents temperature records from nine surface sensors (eight years of records) and three 10 m deep boreholes (4 years of records), installed at locations with different surface and bedrock characteristics. In line with previous studies, our temperature data analyses showed that: micro-meteorology controls the surface temperature, active layer thicknesses are directly related to aspect and ranged from <2 m to nearly 6 m, and that thin accumulations of snow and open fractures are cooling factors. Thermal profiles empirically demonstrated the coexistence within a single rock peak of warm and cold permafrost (about −1.5 to −4.5 °C at 10 m depth) and the resulting lateral heat fluxes. Our results also extended current knowledge of the effect of snow, in that we found similar thermo-insulation effects as reported for gentle mountain areas. Thick snow warms shaded areas, and may reduce active layer refreezing in winter and delay its thawing in summer. However, thick snow thermo-insulation has little effect compared to the high albedo of snow which leads to cooler conditions at the rock surface in areas exposed to the sun. A consistent inflection in the thermal profiles reflected the cooling effect of an open fracture in the bedrock, which appeared to act as a thermal cutoff in the sub-surface thermal regime. Our field data are the first to be obtained from an Alpine permafrost site where borehole temperatures are below −4 °C, and represent a first step towards the development of strategies to investigate poorly known aspects in steep bedrock permafrost such as the effects of snow cover and fractures.

High alpine rock wall permafrost is extremely sensitive to climate change. Its degradation has a strong impact on landscape evolution and can trigger rockfalls constituting an increasing threat to socio-economical activities of highly frequented areas; quantitative understanding of permafrost evolution is crucial for such communities. This study investigates the long-term evolution of permafrost in three vertical cross sections of rock wall sites between 3160 and 4300 m above sea level in the Mont Blanc massif, from the Little Ice Age (LIA) steady-state conditions to 2100. Simulations are forced with air temperature time series, including two contrasted air temperature scenarios for the 21st century representing possible lower and upper boundaries of future climate change according to the most recent models and climate change scenarios. The 2-D finite element model accounts for heat conduction and latent heat transfers, and the outputs for the current period (2010–2015) are evaluated against borehole temperature measurements and an electrical resistivity transect: permafrost conditions are remarkably well represented. Over the past two decades, permafrost has disappeared on faces with a southerly aspect up to 3300 m a.s.l. and possibly higher. Warm permafrost (i.e. > − 2 °C) has extended up to 3300 and 3850 m a.s.l. in N and S-exposed faces respectively. During the 21st century, warm permafrost is likely to extend at least up to 4300 m a.s.l. on S-exposed rock walls and up to 3850 m a.s.l. depth on the N-exposed faces. In the most pessimistic case, permafrost will disappear on the S-exposed rock walls at a depth of up to 4300 m a.s.l., whereas warm permafrost will extend at a depth of the N faces up to 3850 m a.s.l., but possibly disappearing at such elevation under the influence of a close S face. The results are site specific and extrapolation to other sites is limited by the imbrication of local topographical and transient effects.

Mountain permafrost, constituting 30% of the global permafrost area, is sensitive to climate change and strongly impacts mountain ecosystems and communities. This study examines 21st century permafrost warming in European mountains using decadal ground temperature data from sixty-four boreholes in the Alps, Scandinavia, Iceland, Sierra Nevada and Svalbard. During 2013–2022, warming rates at 10 metres depth exceed 1 °C dec⁻¹ in cases, generally surpassing previous estimates because of accelerated warming and the use of a comprehensive data set. Substantial permafrost warming occurred at cold and ice-poor bedrock sites at high elevations and latitudes, at rates comparable to surface air temperature increase. In contrast, latent heat effects in ice-rich ground near 0 °C reduce warming rates and mask important changes of mountain permafrost substrates. The warming patterns observed are consistent across all sites, depths and time periods. For the coming decades, the propagation of permafrost warming to greater depths is largely predetermined already.

L’étude du permafrost de paroi rocheuse a débuté depuis à peine une décennie. La compréhension du rôle de la dégradation du permafrost sur l’instabilité des parois se fonde en premier lieu sur la connaissance de sa distribution spatiale. Les difficultés de la cartographie du permafrost de paroi résultent de son invisibilité et de son extrême sensibilité aux conditions locales, ce qui rend sa modélisation indispensable. Un modèle statistico-empirique élaboré pour cartographier le permafrost à l’échelle des Alpes est ici appliqué au massif du Mont Blanc, en intégrant des variables d’entrée locales à haute résolution spatiale. L’influence de la résolution spatiale du modèle numérique d’altitude utilisé en donnée d'entrée est évaluée : la différence de température de sortie peut atteindre 2°C pour un même modèle entre une résolution à 4 m et une à 30 m. Une cartographie du permafrost des parois du massif est proposée à partir d'un indice permettant estimer sa présence. Il couvrirait de 45 à 79% des 86 km² de parois ≥ 40° du massif ; il pourrait être présent sur quelques secteurs structuralement favorables (fracturation importante) dès 1 900 m d’altitude en face nord et 2 400 m en face sud. Sa présence serait plus continue à partir de 2 600 m en face nord et 3 000 m en face sud, mais il ne couvrirait la totalité des parois qu’à partir de 3 600 m, quelle que soit l’exposition. L’interprétation de la carte d’indice de permafrost nécessite de tenir également compte de l’effet de facteurs autres que le contrôle topoclimatique et non intégrés au modèle, telles que la fracturation et la présence de neige.

Rock wall permafrost is highly sensitive to atmospheric warming. Its degradation is regarded as a primary factor accounting for the recent increase in periglacial rock slope failures. Investigations of rock wall permafrost have so far ignored hydrological processes acting in bedrock fractures. We propose a 2‐D coupled thermal and hydrological modeling approach applied to alpine rock wall permafrost. Simulations are carried out on the scale of the mountain flank for four case studies with variable saturation levels and hydrological forcings. Results show that cold water infiltration from the summit leads to a deeper permafrost body than with no water flows. Ice‐filled fractures first delay permafrost thawing due to latent heat consumption but then accelerate it when the ice starts to melt. Ice may thus subsist in fractures surrounded by thawed bedrock while thawing corridors may form in fractures embedded in frozen bedrock. As a result, temperature gradients are made steeper. When connected fractures thaw, bottom‐up permafrost degradation can occur through upward propagation of thawing wedges delineated by these fractures. High hydraulic head values are associated with the formation of perched water tables above or within the impermeable permafrost body, and correspond to hydrostatic pressures that could reach critical values in terms of rock wall stability. The proposed model setting is more appropriate for investigating long‐term permafrost changes, rock wall permafrost dynamics and hydrogeology across entire mountain flanks, but could be applied on a finer spatial scale to investigate short‐term permafrost response to climate signals and rock wall destabilization.