Rapid 3-D analysis of rockfalls

Stock, Greg M.; Guérin, Antoine; Avdievitch, Nikita; Collins, Brian D.; Jaboyedoff, Michel

doi:10.1130/gsatg374gw.1

Cited by 8 publications

(4 citation statements)

References 6 publications

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“…Not only did instabilities (successive failures of overhangs) propagate upwards, but the involved volumes also increased between 2008 and 2010. A similar erosion system has recently been highlighted 40,86 by means of TLS and SfM monitoring performed in the southeast face of El Capitan (2307 m a.s.l.) in California (Yosemite National Park, USA).…”

Section: Analysis Of the 2008-2011 Rockfall Event Sequence The Retrosupporting

confidence: 54%

The three-stage rock failure dynamics of the Drus (Mont Blanc massif, France) since the June 2005 large event

Guérin

Ravanel

Matasci

et al. 2020

Sci Rep

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Since the end of the Little Ice Age, the west face of the Drus (Mont Blanc massif, France) has been affected by a retrogressive erosion dynamic marked by large rockfall events. From the 1950s onwards, the rock failure frequency gradually increased until the large rockfall event (292,680 m3) of June 2005, which made the Bonatti Pillar disappear. Aiming to characterize the rock failure activity following this major event, which may be related to permafrost warming, the granitic rock face was scanned each autumn between October 2005 and September 2016 using medium- and long-range terrestrial laser scanners. All the point clouds were successively compared to establish a rockfall source inventory and determine a volume-frequency relationship. Eleven years of monitoring revealed a phase of rock failure activity decay until September 2008, a destabilization phase between September 2008 and November 2011, and a new phase of rock failure activity decay from November 2011 to September 2016. The destabilization phase was marked by three major rockfall events covering a total volume of 61,494 m3, resulting in the progressive collapse of a new pillar located in the northern part of the June 2005 rockfall scar. In the same way as for the Bonatti Pillar, rock failure instability propagated upward with increasing volumes. In addition to these major events, 304 rockfall sources ranging from 0.002 to 476 m3 were detected between 2005 and 2016. The temporal evolution of rock failure activity reveals that after a major event, the number of rockfall sources and the eroded volume both follow a rapid decrease. The rock failure activity is characterized by an exponential decay during the period following the major event and by a power-law decay for the eroded volume. The power law describing the distribution of the source volumes detected between 2005 and 2016 indicates an exponent of 0.48 and an average rock failure activity larger of more than six events larger than 1 m3 per year. Over the 1905–2016 period, a total of 426,611 m3 of rock collapsed from the Drus west face, indicating a very high rock wall retreat rate of 14.4 mm year−1 over a surface of 266,700 m2. Averaged over a time window of 1000 years, the long-term retreat rate derived from the frequency density integration of rock failure volumes is 2.9 mm year−1. Despite difficulty in accessing and monitoring the site, our study demonstrates that long-term surveys of high-elevation rock faces are possible and provide valuable information that helps improve our understanding of landscape evolution in mountainous settings subject to permafrost warming.

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Section: Analysis Of the 2008-2011 Rockfall Event Sequence The Retrosupporting

confidence: 54%

The three-stage rock failure dynamics of the Drus (Mont Blanc massif, France) since the June 2005 large event

Guérin

Ravanel

Matasci

et al. 2020

Sci Rep

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“…El Capitan has many prominent exfoliation sheets and has experienced many exfoliation-type rockfalls (Stock et al 2013). The easternmost part of its southeast face was affected by a rockfall sequence during the autumn of 2017 whose largest volume (8,611 m 3 ) collapsed on 28 September 2017 (Stock et al 2018;Guerin et al 2020). Unlike the Rhombus Wall, El Capitan consists of eight different rock units, including three types of granite and two types of dikes (Putnam et al 2015).…”

Section: Study Sites and Geologic Settingmentioning

confidence: 99%

“…Over the past 15 years, the rapid development of remote sensing techniques such as ground-based InSAR and LiDAR has dramatically revolutionized the characterization and monitoring of rock mass deformation (Slob and Hack 2004;Rosser et al 2007;Sitar 2005, 2008;Oppikofer et al 2009;Derron et al 2011;Jaboyedoff et al 2012;Dehls et al 2014;Rouyet et al 2017). High spatio-temporal resolution monitoring of rock cliffs using terrestrial laser scanning (TLS) point clouds (e.g., Abellán et al 2009Abellán et al , 2010Rosser et al 2013;Royán et al 2014Royán et al , 2015Kromer et al 2015aKromer et al , 2018Stock et al 2018) has shown that it is possible in some cases to detect precursor deformations below centimetric scale and to monitor them over time until failure. In addition to obtaining a more comprehensive rockfall inventory and a more realistic volume-frequency relationship (Barlow et al 2012;van Veen et al 2017;Williams et al 2018Williams et al , 2019, near real-time TLS surveys offer new opportunities to better anticipate failure (Eitel et al 2016;Kromer et al 2015bKromer et al , 2017.…”

Section: Introductionmentioning

confidence: 99%

Remote thermal detection of exfoliation sheet deformation

et al. 2020

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A growing body of research indicates that rock slope failures, particularly from exfoliating cliffs, are promoted by rock deformations induced by daily temperature cycles. Although previous research has described how these deformations occur, full three-dimensional monitoring of both the deformations and the associated temperature changes has not yet been performed. Here we use integrated terrestrial laser scanning (TLS) and infrared thermography (IRT) techniques to monitor daily deformations of two granitic exfoliating cliffs in Yosemite National Park (CA, USA). At one cliff, we employed TLS and IRT in conjunction with in situ instrumentation to confirm previously documented behavior of an exfoliated rock sheet, which experiences daily closing and opening of the exfoliation fracture during rock cooling and heating, respectively, with a few hours delay from the minimum and maximum temperatures. The most deformed portion of the sheet coincides with the area where both the fracture aperture and the temperature variations are greatest. With the general deformation and temperature relations established, we then employed IRT at a second cliff, where we remotely detected and identified 11 exfoliation sheets that displayed those general thermal relations. TLS measurements then subsequently confirmed the deformation patterns of these sheets showing that sheets with larger apertures are more likely to display larger thermal-related deformations. Our high-frequency monitoring shows how coupled TLS and IRT allows for remote detection of thermally induced deformations and, importantly, how IRT could potentially be used on its own to identify partially detached exfoliation sheets capable of large-scale deformation. These results offer a new and efficient approach for investigating potential rockfall sources on exfoliating cliffs.

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“…1a,b). Over the past 150 years, rockfalls have been intermittently documented 9 from the southeast face of El Capitan, with 45 rockfalls recorded 6,71 between 1857 and 2017. Exfoliation sheets are characteristic of the Yosemite landscape 72,73 , and are ubiquitous on El Capitan.…”

Section: Study Sitementioning

confidence: 99%

Detection of rock bridges by infrared thermal imaging and modeling

Jaboyedoff

Collins

et al. 2019

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Characterization of rock discontinuities and rock bridges is required to define stability conditions of fractured rock masses in both natural and engineered environments. Although remote sensing methods for mapping discontinuities have improved in recent years, remote detection of intact rock bridges on cliff faces remains challenging, with their existence typically confirmed only after failure. In steep exfoliating cliffs, such as El Capitan in Yosemite Valley (California, USA), rockfalls mainly occur along cliff-parallel exfoliation joints, with rock bridges playing a key role in the stability of partially detached exfoliation sheets. We employed infrared thermal imaging (i.e., thermography) as a new means of detecting intact rock bridges prior to failure. An infrared thermal panorama of El Capitan revealed cold thermal signatures for the surfaces of two granitic exfoliation sheets, consistent with the expectation that air circulation cools the back of the partially detached sheets. However, we also noted small areas of warm thermal anomalies on these same sheets, even during periods of nocturnal rock cooling. Rock attachment via rock bridges is the likely cause for the warm anomalies in the thermal data. 2-D model simulations of the thermal behavior of one of the monitored sheets reproduce the observed anomalies and explain the temperature differences detected in the rock bridge area. Based on combined thermal and ground-based lidar imaging, and using geometric and rock fracture mechanics analysis, we are able to quantify the stability of both sheets. Our analysis demonstrates that thermography can remotely detect intact rock bridges and thereby greatly improve rockfall hazard assessment.

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Rapid 3-D analysis of rockfalls

Cited by 8 publications

References 6 publications

The three-stage rock failure dynamics of the Drus (Mont Blanc massif, France) since the June 2005 large event

The three-stage rock failure dynamics of the Drus (Mont Blanc massif, France) since the June 2005 large event

Remote thermal detection of exfoliation sheet deformation

Detection of rock bridges by infrared thermal imaging and modeling

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