Thermo‐cryogenic controls of fracture kinematics in permafrost rockwalls

Draebing, Daniel; Krautblatter, Michael; Hoffmann, Thomas

doi:10.1002/2016gl072050

Cited by 73 publications

(94 citation statements)

References 79 publications

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“…Once ice-free, strong diurnal and seasonal variations are likely to induce pronounced thermal stress leading to deformation (Hasler et al, 2012;Weber et al, 2017) and potentially to failure along critically-stressed discontinuities 360 (Hall, 1999;Gischig et al, 2011). Additionally, cyclic freeze-thaw action will cause rock fatigue (Jia et al, 2015), hydrofracture (Davidson and Nye, 1985;Sass, 2004) and the expansion of water-filled joints (Matsuoka and Murton, 2008), all of which promote destabilization in recently deglaciated rockwall sections (Draebing et al, 2017).…”

Section: Deglaciation-induced Thermomechanical Forcing and Active Laymentioning

confidence: 99%

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

Hartmeyer¹,

Delleske²,

Keuschnig³

et al. 2020

Preprint

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In the European Alps almost half the glacier volume disappeared over the past 150 years. The loss is reflected in 10 glacier retreat and ice surface lowering even at high altitude. In steep glacial cirques surface lowering exposes rock to atmospheric conditions for the very first time in many millennia. Instability of rockwalls has long been identified as one of the direct consequences of deglaciation, but so far cirque-wide quantification of rockfall at high-resolution is missing. Based on terrestrial LiDAR a rockfall inventory for the permafrost-affected rockwalls of two rapidly deglaciating cirques in the Central Alps of Austria (Kitzsteinhorn) is established. Over six-years (2011-2017) 78 rockwall scans were acquired to generate data 15 of high spatial and temporal resolution. 632 rockfalls were registered ranging from 0.003 to 879.4 m³, mainly originating from pre-existing structural rock weaknesses. 60 % of the rockfall volume detached from less than ten vertical meters above the glacier surface, indicating enhanced rockfall activity over tens of years following deglaciation. Debuttressing seems to play a minor effect only. Rather, preconditioning is assumed to start inside the Randkluft (gap between cirque wall and glacier) where sustained freezing and ample supply of liquid water likely cause enhanced physical weathering and high plucking stresses. 20Following deglaciation, pronounced thermomechanical strain is induced and an active layer penetrates into the formerly perennially frozen bedrock. These factors likely cause the observed paraglacial rockfall increase close to the glacier surface. This paper presents the most extensive dataset of high-alpine rockfall to date and the first systematic documentation of a cirquewide erosion response of glaciated rockwalls to recent climate warming.

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Section: Deglaciation-induced Thermomechanical Forcing and Active Laymentioning

confidence: 99%

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

Hartmeyer¹,

Delleske²,

Keuschnig³

et al. 2020

Preprint

Self Cite

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“…Tectonic stresses arise due to ongoing plate motions in Earth's crust that can also interact with topography to enhance stress [Martel, 2006]. Finally, we define environmental stresses as those that comprise all climate-and environment-related stresses including freezing [e.g., Draebing et al, 2017], salt precipitation [e.g., Amit et al, 1993], mineral hydration [e.g., Burnett et al, 2008], biologic activity [e.g., Viles, 2012], and thermal cycling [e.g., Freire-Lista et al, 2016]. Both tectonic and topographic stresses might be considered static, but virtually all environmental stresses are cyclic at some periodicity (e.g., diurnal, seasonal, and annual).…”

Section: Introductionmentioning

confidence: 99%

Mechanical weathering and rock erosion by climate‐dependent subcritical cracking

Eppes

Keanini

2017

Reviews of Geophysics

195

150

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This work constructs a fracture mechanics framework for conceptualizing mechanical rock breakdown and consequent regolith production and erosion on the surface of Earth and other terrestrial bodies. Here our analysis of fracture mechanics literature explicitly establishes for the first time that all mechanical weathering in most rock types likely progresses by climate‐dependent subcritical cracking under virtually all Earth surface and near‐surface environmental conditions. We substantiate and quantify this finding through development of physically based subcritical cracking and rock erosion models founded in well‐vetted fracture mechanics and mechanical weathering, theory, and observation. The models show that subcritical cracking can culminate in significant rock fracture and erosion under commonly experienced environmental stress magnitudes that are significantly lower than rock critical strength. Our calculations also indicate that climate strongly influences subcritical cracking—and thus rock weathering rates—irrespective of the source of the stress (e.g., freezing, thermal cycling, and unloading). The climate dependence of subcritical cracking rates is due to the chemophysical processes acting to break bonds at crack tips experiencing these low stresses. We find that for any stress or combination of stresses lower than a rock's critical strength, linear increases in humidity lead to exponential acceleration of subcritical cracking and associated rock erosion. Our modeling also shows that these rates are sensitive to numerous other environment, rock, and mineral properties that are currently not well characterized. We propose that confining pressure from overlying soil or rock may serve to suppress subcritical cracking in near‐surface environments. These results are applicable to all weathering processes.

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“…Precursory displacements or small failures in advance of the final full failure are the result of internal failure processes such as fracture propagation or sliding (Eberhardt et al, 2004;Petley, 2004). Measuring relative surface displacements and spatial patterns are common approaches to monitor kinematic properties aiming to identify environmental forcing (Blikra & Christiansen, 2014;Draebing et al, 2017;Hasler et al, 2012;Matsuoka & Murton, 2008;Nordvik et al, 2010;Weber et al, 2017;Wegmann & Gudmundsson, 1999). However, the separation of distinct patterns that are indicative of progression toward a rock slope failure from background processes often remains difficult if not impossible, because each point measurement is dominated by local effects rather representing the general behavior of the whole slope (Rosser et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Acoustic and Microseismic Characterization in Steep Bedrock Permafrost on Matterhorn (CH)

et al. 2018

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Understanding of processes and factors influencing slope stability is essential for assessing the stability of potentially hazardous slopes. Passive monitoring of acoustic emissions and microseismology provides subsurface information on fracturing (timing and identification of the mechanism) and therefore complement surface displacement data. This study investigates for the first time acoustic and microseismic signals generated in steep, fractured bedrock permafrost, covering the broad frequency range of 1 − 105 Hz. The analysis of artificial forcing experiments using a rebound hammer in a controlled setting led to two major findings: First, statistically insignificant cross correlation between signals indicates that waveforms change strongly with propagation distance. Second, a significant amplification is found in the frequency band 33–67 Hz. This finding is strongly supported by evidence from artificial rockfall events and more importantly by naturally occurring fracture events identified in fracture displacement data. Thus, filtering this frequency band enables enhanced detection of microseismic events relevant for slope stability assessment. The analysis of 2‐year time series in this frequency band further suggests that the detected energy rate baseline of all automatically triggered events using the STA/LTA algorithm is not sensitive to temperature forcing, an observation of primary importance for long‐term data collection, analysis, and interpretation. The event detection in the established frequency band is not only improved but also not affected by the short‐ and long‐term temperature changes in such a rapidly changing environment.

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Thermo‐cryogenic controls of fracture kinematics in permafrost rockwalls

Cited by 73 publications

References 79 publications

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

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

Mechanical weathering and rock erosion by climate‐dependent subcritical cracking

Acoustic and Microseismic Characterization in Steep Bedrock Permafrost on Matterhorn (CH)

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