No abstract

This study analyses the factors controlling variations in short‐term, seasonal and multiyear deformation velocity of an alpine rock glacier from data obtained over periods of 1–20 years. The Ritigraben rock glacier, in the western Swiss Alps, was monitored using tacheometry, terrestrial laser scanning, an in situ global positioning system and borehole deformation measurements. Rock glacier stratigraphy and ground temperature data were obtained from boreholes, and long‐term meteorological data (temperature, precipitation, snow water equivalent) from nearby weather stations. Shearing within a distinct water‐bearing layer represents the major component of the displacement. Short‐term accelerations and seasonal velocity patterns of the rock glacier deformation appear to have been triggered by water supply to this layer. A long‐term acceleration of the rock glacier was probably also caused by increased water supply. Permafrost temperature in the rock glacier has increased slightly since 2002, yet no direct causality could be established between this limited warming and rock glacier acceleration. Copyright © 2017 John Wiley & Sons, Ltd.

Observations show that considerable amounts of snow can accumulate in steep, rough rock walls. The heterogeneously distributed snow cover significantly affects the surface energy balance and hence the thermal regime of the rock walls. To assess the small-scale variability of snow depth and rock temperatures in steep north and south facing rock walls, a spatially distributed multi-method approach is applied at Gemsstock, Switzerland, combining 35 continuous near-surface rock temperature measurements, high resolution snow depth observations using terrestrial laser scanning, as well as in-situ snow pit investigations. The thermal regime of the rock surface is highly dependent on short-and longwave radiation, albedo, surface roughness, snow depth and on snow distribution in time and space. Around 2 m of snow can accumulate on slopes with angles up to 75°, due to micro-topographic structures like ledges. Hence, contrasts in mean annual rock surface temperature between the north and the south facing slopes are less than 4°C. However, significant small-scale variability of up to 10°C in mean daily rock surface temperature occurs within a few metres over the rock walls due to the variable snow distribution, revealing the heterogeneity and complexity of the thermal regime at a very local scale. In addition, multiple linear regression could explain up to 77% of near-surface rock temperature variability, which underlines the importance of radiation and snow depth and thus also of the topography. In the rock faces the thermal insulation of the ground starts with snow depths exceeding 0.2 m. This is due to the high thermal resistance of a less densely packed snow cover, especially in the north facing slope. Additionally, aspect induced differences of snow cover characteristics and consequently thermal conductivities are observed in the rock walls.

The aim of this study is to investigate the influence of snow on permafrost and rock stability at the Steintaelli (Swiss Alps). Snow depth distribution was observed using terrestrial laser scanning and time‐lapse photography. The influence of snow on the rock thermal regime was investigated using near‐surface rock temperature measurements, seismic refraction tomography and one‐dimensional thermal modelling. Rock kinematics were recorded with crackmeters. The distribution of snow depth was strongly determined by rock slope micro‐topography. Snow accumulated to thicknesses of up to 3.8 m on less steep rock slopes (<50°) and ledges, gradually covering steeper (up to 75°) slopes above. A perennial snow cornice at the flat ridge, as well as the long‐lasting snow cover in shaded, gently inclined areas, prevented deep active‐layer thaw, while patchy snow cover resulted in a deeper active‐layer beneath steep rock slopes. The rock mechanical regime was also snow‐controlled. During snow‐free periods, high‐frequency thermal expansion and contraction occurred. Rock temperature locally dropped to ‐10 °C, resulting in thermal contraction of the rock slopes. Snow cover insulation maintained temperatures in the frost‐cracking window and favoured ice segregation. Daily thermal‐induced and seasonal ice‐induced fracture kinematics were dominant, and their repetitive occurrence destabilises the rock slope and can potentially lead to failure. Copyright © 2016 John Wiley & Sons, Ltd.

An increasing number of studies highlight the controlling influence of water on rock glacier deformation velocities. The link between the concept of water‐driven shearing processes and numerous observations of correlating mean annual air or ground temperatures and rock glacier velocities is discussed here. We present a dataset measured at the Schafberg rock glacier in the Eastern Swiss Alps, complemented by temperature data from three other rock glaciers in the Swiss Alps, which allowed us to reconstruct the processes influencing both mean annual ground temperatures and rock glacier deformation velocity. Rock glacier hydrology is the parameter linking rock glacier temperature and velocities and is a crucial influencing factor. The main external forcing parameter appart from mean annual air temperature is early winter snow coverage. The study shows that the concept of water being a controlling factor for rock glacier velocity is no contradiction to the observed correlations between air or ground temperature and rock glacier deformation.