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Spatial and temporal evolution of rock fall activity on a failing slope
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The Great Aletsch Region (GAR, Swiss Alps) has undergone to several cycles of glacial advancement and retreat, which have deeply affected the evolution of the surrounding landscape. Currently, this region is one of the places where the effects of climate change can be strikingly observed, as the Aletsch glacier is experiencing a remarkable retreat with rates in
the order of 50 meters every year. In particular, a deep-seated slope instability located in the area called “Moosfluh” has shown during the past 20 years evidences of a slow but progressive increase of surface displacement. The moving mass associated to the Moosfluh rockslide affects an area of about 2 square km and entails a volume estimated in the order of 150-200 millions of cubic meters. In the late summer 2016, an unusual acceleration of the Moosfluh rockslide was observed. Compared to previous years, when ground deformations were in the order of few centimeters, in the period September-October 2016 maximum velocities have reached locally up to 0.8 meters per day. Such a critical evolution caused the generation of several deep tensile cracks, and resulted in an increased number of rock failures at different locations of the landslide body. These processes have been observed at several other unstable rock slopes prior to catastrophic failure events (Rosser et al., 2007); however, high resolution monitoring data are rare. The main goal of the study is to compare and possibly correlate the spatial and temporal evolution of surface deformation with the occurrence, the location and the size of rock falls events. This may help to better characterize the kinematic evolution of the Moosfluh rock slope, and more in general of large rock slope instabilities showing signs of a potential catastrophic failure.
Due to the limited access to the site, rock falls will be identified and investigated by analyzing the data acquired remotely, including (i) a seismic network composed of 3 Raspberry Shake (RS) seismometers, and (ii) a webcam installed on the opposite side of the Moosfluh slope (see locations in Figure 2 of the attached Poster presentation). RS are a low-cost, all-in-one plug-and-go solution developed by OSOP S.A., which integrate vertical velocity sensor (4.5 Hz Racotech RGI-20DX), digitizer, and computer in a single box (100x120x50 mm, 0.35 kg). On 17 May we installed the first seismometer (RS1), the RS2 occurred 21 June, and the RS3 on 6 July 2017. We expect to record a further increase of deformation and rock fall activity during the summer. Seismic data will be collected and analyzed by using different approaches and algorithms to identify and locate rock fall phenomena (e.g., Manconi et al., 2016). Regarding the webcam data, rock fall processes will be observed and measured by applying Digital Image Correlation (DIC) algorithms. The webcam acquires images every 10 minutes, and despite the moderate resolution of the webcam picture (5 MPixel), preliminary results have shown that both surface displacement as well as location of local rock slope failure can be traced with change detection approaches.

References:

Manconi, A., Picozzi, M., Coviello, V., De Santis, F., Elia, L., 2016. Real-time detection, location, and
characterization of rockslides using broadband regional seismic networks. Geophys. Res. Lett. 43, 2016GL069572. doi:10.1002/2016GL069572

Rosser, N., Lim, M., Petley, D., Dunning, S., Allison, R., 2007. Patterns of precursory rockfall prior to slope
failure. J. Geophys. Res. Earth Surf. 112, F04014. doi:10.1029/2006JF000642
Géologie, géomorphologie, sismologie
Outils des géosciences
rock fall, seismic detection, digital image correlation, rock slope instability
2017
2020
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En cours
Organisation
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Localisation
Valais
Livrables
  • Spatial and temporal evolution of rock fall activity on a failing slope, Andrea Manconi*, Franziska Glueer, and Simon Loew (2017, Présentation).
    Poster_PRF_2017.png
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Ce projet a été cofinancé par les services cantonaux suivants : SFP, SPE, SRTCE et SEFH© Crealp 2015