The Efficacy of Frost Weathering Processes in Alpine Rockwalls

Abstract

Weathering processes prepare and trigger rockfall, which is a key agent of alpine landscape evolution and a hazardous process. The relative importance of different weathering processes is hard to decipher; nevertheless, current knowledge assumes a dominant role of frost cracking in eroding alpine rockwalls. This study uses a laboratory approach to simulate volumetric expansion and ice segregation in four alpine rock samples, monitors crack deformation, and quantifies frost weathering efficacy. Our results show that short‐term volumetric expansion in cracks provides stresses up to 10 MPa over hours, while long‐term ice segregation causes stresses of 1 MPa over days. While volumetric expansion in fall can reach critical fracture levels, volumetric expansion in early summer and ice segregation rather approaches subcritical fracture propagation levels. We conclude that subcritical crack propagation is the dominant antecedent process of rockfall initiation, which can be amplified by rare critical cracking due to volumetric expansion.

Current glacier recession causes significant rockfall increase: The immediate paraglacial response of deglaciating cirque walls

“…This observation has recently been substantiated by numerous field and lab experiments demonstrating intense frost cracking at temperatures just below 0 °C (Girard et al, 2013;Duca et al, 2014;Murton et al, 2016) and thermo-cryogenic rock fatigue due to damage accumulation over longer time scales (Jia et al, 2015). Subcritical stress propagation driven by sustained freezing and sufficient 345 water supply (Jia et al, 2017;Draebing and Krautblatter, 2019), and high plucking-related tensile stresses caused by refreezing meltwater at the bottom of the Randkluft (Lewis, 1938;Hooke, 1991). We hypothesize, therefore, that they are the dominant antecedent processes of rockfall preparation.…”

Identification of rock and fracture kinematics in high Alpine rockwalls under the influence of altitude

“…I assume that the rock samples are representative for the rockwall. For a more detailed description of the rock samples and their mechanical properties see Draebing and Krautblatter (2019). On each rock sample (Fig.…”

“…Current research highlights the role of mechanical weathering (Eppes and Keanini, 2017). Diurnal and seasonal ambient meteorological changes causing cyclic heating and cooling (Collins and Stock, 2016;Gunzburger and Merrien-Soukatchoff, 2011), wet-dry cycles (Zhang et al, 2015), freeze-thaw cycles (Matsuoka, 2001(Matsuoka, , 2008 or active-layer thaw (Draebing et al, 2017a;Draebing et al, 2014) produce critical and subcritical stresses that propagate micro-fractures (Draebing and Krautblatter, 2019;Eppes et al, 2018). Several studies investigated the influence of thermal changes on rockwalls and demonstrated the sudden erosion by thermal shock (Collins et al, 2019;Collins et al, 2018) and slow thermal-induced propagation of fractures in Alpine rockwalls (Weber et al, 2017;Hasler et al, 2012;Collins and Stock, 2016) that continuously weakens rock and can trigger rockfall (Ishikawa et al, 2004;Collins and Stock, 2016).…”

“…Matsuoka (2001Matsuoka ( , 2008 observed volumetric expansion induced fracture opening during sudden cooling events in autumn and due to refreezing of meltwater in late spring and early summer. Draebing and Krautblatter (2019) recently simulated this process in the laboratory and showed that volumetric expansion due to refreezing causes subcritical stresses and freezing of saturated fractures are rare but can develop critical stresses. In contrast, ice segregation causes stresses by a thermally induced suction that result in water migration to the freezing front (Matsuoka and Murton, 2008).…”

“…In contrast, ice segregation causes stresses by a thermally induced suction that result in water migration to the freezing front (Matsuoka and Murton, 2008). This process operates on seasonal scales, can crack intact rocks (Murton et al, 2006) or widen existing fractures (Draebing and Krautblatter, 2019;Draebing et al, 2017b) and cause subcritical stresses (Draebing and Krautblatter, 2019).…”