Remote thermal detection of exfoliation sheet deformation
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Antoine Guerin I Michel Jaboyedoff I Brian D. Collins I Greg M. Stock I Marc-Henri Derron I Antonio Abellán I Battista Matasci
Remote thermal detection of exfoliation sheet deformation
Abstract 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 largescale deformation. These results offer a new and efficient approach for investigating potential rockfall sources on exfoliating cliffs. Keywords Exfoliation . Rockfall source . Terrestrial laser scanning . Infrared thermography . Yosemite Valley Introduction Rock slope failure leading to rockfall is a dynamic erosional process that controls the evolution of many landscapes and, in particular, steep bedrock formations (Varnes 1978; Hutchinson 1988; Evans and Hungr 1993; Hungr et al. 1999; Rosser et al. 2005; Rabatel et al. 2008; Stock and Uhrhammer 2010; Krautblatter et al. 2012; Janeras et al. 2017). The identification of potential rockfall sources and the detection of deformations prior to failure are crucial for improving rockfall hazard assessment (Terzaghi 1962; Saito 1969; Fukuzono 1985; Zvelebill and Moser 2001; Crosta and Agliardi 2003; Corominas et al. 2005). 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; Collins and Sitar 2005, 2008; Oppikof
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