Topographic and Geologic Controls on Frost Cracking in Alpine Rockwalls

Draebing, Daniel; Mayer, Till Felix

doi:10.1029/2021jf006163

Cited by 17 publications

(34 citation statements)

References 118 publications

(346 reference statements)

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“…Grosse Grabe North Pillar, as indicated by the modelling results of rock walls at similar elevation and exposition (Draebing & Mayer, 2021). This way, frost weathering is preparing rock wall instabilities, subsequently triggered by processes in summer such as thermal stresses described above.…”

Section: Conditions Leading To Rock Wall Destabilizationmentioning

confidence: 67%

“…The cumulative and repetitive nature of thermally induced failure mechanisms is considered an important preparatory factor for rockfall in fractured rock masses exposed to large temperature oscillations (Bakun‐Mazor et al, 2020; Collins & Stock, 2016; Draebing et al, 2017; Gunzburger et al, 2005). Although no in‐situ rock temperatures were measured at the south‐facing rock wall of Grosse Grabe, similar south‐exposed rock walls yield a daily temperature variation of up to 16.5°C compared to only 4°C for north‐facing rock walls as a result of solar radiation differences (Draebing & Mayer, 2021). While daily temperature changes only penetrate down to shallow depths (≤0.4 m) (Gunzburger et al, 2005), seasonal thermal changes can propagate deeper in highly fractured bedrock (up to 100 m) due to air convection (Gischig et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

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Timing, volume and precursory indicators of rock‐ and cliff fall on a permafrost mountain ridge (Mattertal, Switzerland)

Hendrickx

Roy

Helmstetter

et al. 2022

Earth Surf Processes Landf

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High mountain environments are increasingly affected by rockfall‐related hazards, driven by climate change. Studying rockfall in these environments is, however, challenging due to the inaccessibility of mountain ridges and the complex interaction between controlling factors. In this study, the rock wall of Grosse Grabe North Pillar in the Matter valley (Western Swiss Alps) was studied in detail over a timespan of 4 years (2017–2021). Data was collected from time‐lapse photography, terrestrial laser scanning, unmanned aerial vehicle photogrammetry and seismic measurements. The presented dataset is unique because data collection started before the onset of the rock wall destabilization, allowing us to understand precursory indicators of large‐scale events. In total, we recorded 382 rock‐ and cliff fall events (100–31 300 m3), with a total volume of 204 323 ± 8173 m3, resulting in a scar depth of ~40 m. An associated rock wall retreat rate of 71.2 ± 2.8 mm year−1 was calculated for the 1991–2021 period. Highly fractured south‐exposed gneiss lithology is viewed as the main predisposition for the observed rock‐ and cliff fall events, allowing high‐temperature oscillations to cause irreversible movements at fracture level. Cliff falls (104–106 m3) were preluded by an outward movement of the rock wall that started to increase 1.5 years before any significant collapse of the rock wall, reaching locally up to 30 cm. All cliff fall events occurred in summer, exposing ice in the clefts. This is assumed to be the base of the permafrost from the north side. Rapid permafrost degradation is viewed as a triggering factor after its exposure, causing progressive failure of the rock wall, leading to very high rock wall retreat rates on a decadal timescale.

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Section: Conditions Leading To Rock Wall Destabilizationmentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Timing, volume and precursory indicators of rock‐ and cliff fall on a permafrost mountain ridge (Mattertal, Switzerland)

Hendrickx

Roy

Helmstetter

et al. 2022

Earth Surf Processes Landf

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“…Therefore, the effect of these different mechanisms can be studied. Frost‐weathering sets in when the daily mean air temperature drops below a freezing temperature threshold and snow depth is below a threshold to not insulate the bedrock (e.g., Draebing & Mayer, 2021). Rainfall‐induced landslides happen when daily rainfall exceeds a threshold (e.g., Leonarduzzi et al., 2017).…”

Section: Methodsmentioning

confidence: 99%

Numerical Investigation of Sediment‐Yield Underestimation in Supply‐Limited Mountain Basins With Short Records

Hirschberg

McArdell

Bennett

et al. 2022

Geophysical Research Letters

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Climate and sediment supply are critical for geomorphic systems. It is known that complex relations between such forcings and sediment mobilization may lead to dampened or erased environmental signals in sediment records. But it is unclear under which circumstances environmental signals are transmitted and measurable downstream. We used a numerical approach consisting of a sediment cascade model and a stochastic weather generator to quantify climate forcing effects under a range of sediment supply regimes in a debris‐flow catchment in the Swiss Alps (Illgraben). We show that sediment yields estimated from short records are highly uncertain both in terms of mean and interannual variability. Furthermore, sediment yields tend to be underestimated in supply‐limited systems, where also long‐term memory effects, driven by the history of sediment storage, are evident. Consequently, determining geomorphic system response from short records may be grossly inaccurate and should be extended with sediment supply detection and uncertainty analysis.

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“…This will affect especially rockwalls located at lower elevations; therefore, cryogenic processes and triggered rockfall will be shifted to higher elevations. At higher elevations, the climate-change-induced changes in the temperature regime will also affect permafrost rockwalls, decrease rockwall stability (Krautblatter et al, 2013;Draebing et al, 2014) and increase rockfall activity due to increased thawing amplified by temperature extremes (Gruber et al, 2004a;Ravanel et al, 2017). Rockfall should be quantified and linked to climatic drivers to predict the effects of climate change on rockfall more accurately.…”

Section: Altitudinal Effects On Rock and Fracture Kinematics And Implications For Rock Stabilitymentioning

confidence: 99%

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

Section: Introductionmentioning

confidence: 99%

Identification of rock and fracture kinematics in high alpine rockwalls under the influence of elevation

Draebing

2021

Earth Surf. Dynam.

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Abstract. In alpine environments, tectonic processes, past glaciation and weathering processes fracture rock and prepare or trigger rockfalls, which are important processes of rock slope evolution and natural hazards. In this study, I quantify thermally and ice-induced rock and fracture kinematics and place these in the context of their role in producing rockfall and climate change. I conducted laboratory measurements on intact rock samples and installed temperature loggers and crackmeters at four rockwalls reaching from 2585 to 2935 m in elevation in the Hungerli Valley, Swiss Alps. My laboratory data show that thermal expansion followed three phases of rock kinematics, which resulted in a hysteresis effect. In the field, control crackmeters on intact rock reflected these temperature phases, and based on thermal expansion coefficients of these observed phases, I modelled thermal stress. Model results show that thermal stress magnitudes were predominantly below rock strengths. Crackmeters across fractures revealed fracture opening during cooling and reverse closing behaviour during warming on daily timescales. Elevation-dependent snow cover controlled the number of daily temperature changes and thermal stresses affecting both intact and fractured rock, while the magnitude is controlled by topographic factors influencing insolation. On a seasonal scale, slow ice-segregation-induced fracture opening can occur within lithology-dependent temperature regimes called frost cracking windows. Shear plane dipping controlled whether fractures opened or closed irreversibly with time due to thermally induced block crawling on an annual scale. Climate change will shorten snow duration and increase temperature extremes and will, therefore, affect the number and the magnitude of thermal changes and associated stresses. Earlier snowmelt in combination with temperature increase will shift the ice-induced kinematic processes to higher elevations. In conclusion, climate change will affect and change rock and fracture kinematics and, therefore, change rockfall patterns in alpine environments. Future work should quantify rockfall patterns and link these patterns to climatic drivers.

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Topographic and Geologic Controls on Frost Cracking in Alpine Rockwalls

Cited by 17 publications

References 118 publications

Timing, volume and precursory indicators of rock‐ and cliff fall on a permafrost mountain ridge (Mattertal, Switzerland)

Timing, volume and precursory indicators of rock‐ and cliff fall on a permafrost mountain ridge (Mattertal, Switzerland)

Numerical Investigation of Sediment‐Yield Underestimation in Supply‐Limited Mountain Basins With Short Records

Identification of rock and fracture kinematics in high alpine rockwalls under the influence of elevation

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