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.[1] The mechanisms that control climate-dependent rockfall from permafrost mountain slopes are currently poorly understood. In this study, we present the results of an extensive rock slope monitoring campaign at the Matterhorn (Switzerland) with a wireless sensor network. A negative dependency of cleft expansion relative to temperature was observed at all clefts for the dominant part of the year. At many clefts this process is interrupted by a period with increased opening and shearing activity in the summer months. More specific, this period lasts from sustained melting within the cleft to the first freezing in autumn. Based on these empirical findings we identify two distinct process regimes governing the cleft motion observed. Combining current theories with laboratory evidence on rock slope movement and stability, we postulate that (1) the negative temperaturedependency is caused by thermomechanical forcing and is reinforced by cryogenic processes during the freezing period and, (2) the enhanced movement in summer originates from a hydro-thermally induced strength reduction in clefts containing perennial ice. It can be assumed that the irreversible part of the process described in (1) slowly modifies the geometric settings and cleft characteristics of permafrost rock slopes in the long term. The thawing related processes (2) can affect stability within hours or weeks. Such short-term stability minima may activate rock masses subject to the slow changes and lead to acceleration and failure.

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.

[1] Frost cracking, the breakdown of rock by freezing, is one of the most important mechanical weathering processes acting on Earth's surface. Insights on the mechanisms driving frost cracking stem mainly from laboratory and theoretical studies. Transferring insights from such studies to natural conditions, involving jointed bedrock and heterogeneous thermal and hydrological properties, is a major challenge. We address this problem with simultaneous in situ measurements of acoustic emissions, used as proxy of rock damage, and rock temperature/moisture content. The 1 year data set acquired in an Alpine rock wall shows that (1) liquid water content has an important impact on freezinginduced rock damage, (2) sustained freezing can yield much stronger damage than repeated freeze-thaw cycling, and (3) that frost cracking occurs over the full range of temperatures measured extending from 0 down to -15°C. These new measurements yield a slightly different picture than previous field studies where ice segregation appears to play an important role. Citation: Girard, L., S. Gruber, S. Weber, and J. Beutel (2013), Environmental controls of frost cracking revealed through in situ acoustic emission measurements in steep bedrock,

Abstract. In recent years, strong variations in the speed of rock glaciers have been detected, raising questions about their stability under changing climatic conditions. In this study, we present continuous time series of surface velocities over 3 years of six GPS stations located on three rock glaciers in Switzerland. Intra-annual velocity variations are analysed in relation to local meteorological factors, such as precipitation, snow(melt), and air and ground surface temperatures. The main focus of this study lies on the abrupt velocity peaks, which have been detected at two steep and fast-moving rock glacier tongues ( ≥  5 m a−1), and relationships to external meteorological forcing are statistically tested.The continuous measurements with high temporal resolution allowed us to detect short-term velocity peaks, which occur outside cold winter conditions, at these two rock glacier tongues. Our measurements further revealed that all rock glaciers experience clear intra-annual variations in movement in which the timing and the amplitude is reasonably similar in individual years. The seasonal decrease in velocity was typically smooth, starting 1–3 months after the seasonal decrease in temperatures, and was stronger in years with colder temperatures in mid winter. Seasonal acceleration was mostly abrupt and rapid compared to the winter deceleration, always starting during the zero curtain period. We found a statistically significant relationship between the occurrence of short-term velocity peaks and water input from heavy precipitation or snowmelt, while no velocity peak could be attributed solely to high temperatures. The findings of this study further suggest that, in addition to the short-term velocity peaks, the seasonal acceleration is also influenced by water infiltration, causing thermal advection and an increase in pore water pressure. In contrast, the amount of deceleration in winter seems to be mainly controlled by winter temperatures.

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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.