1 Principles of progressive failure and aim of this contribution

Progressive failure is generally understood as a gravitational slope deformation that lasts over a certain period of time and accelerates prior to catastrophic failure. Several studies suggested hypothetical failure curves (e.g., Crosta and Agliardi 2003; Xue et al. 2014), all of them including an initiation, a steady state creep and an acceleration phase that might be extremely short when external trigger mechanisms such as earthquakes or strong rainfall events apply (Hermanns and Longva 2012). Most focus has been given so far to detecting the acceleration phase as this helps to identify the potentially damaging event; the inverse-velocity method has been suggested in order to predict the failure moment and make early-warning and successful evacuation possible (Fukuzono 1985; Voight 1989; Crosta and Agliardi 2003). However, accelerated movement can only be detected when long-term slip rates and initiation of sliding is known. This contribution summarizes three datasets on rock slope failures in western Norway

  1. a dataset on unstable rock slopes,

  2. a dataset on ages determined by cosmogenic nuclide dating (CN) of prehistoric catastrophic rock slope failures, and

  3. a dataset of published (Hermanns et al. 2012, 2013) and preliminary results of CN surface exposure ages of sliding surfaces.

This combination of datasets allows improved discussion of initiation and development (creep phase) of failure over time.

2 Unstable rock slopes within Norway

A systematic analysis for unstable rock slopes using aerial photos, satellite-based InSAR, high-resolution airborne LIDAR data, helicopter reconnaissance and field mapping has been carried out in Møre and Romsdal and Sogn og Fjordane (western Norway). A total of 138 unstable rock slopes with post-glacial, gravitationally induced rock slope deformation have been detected so far (Böhme et al. 2011; Saintot et al. 2011; Oppikofer et al. 2015). This dataset is believed to be a nearly complete dataset for unstable rock slopes in the area. Few new sites might however be detected on densely vegetated slopes when the full cover of these counties with high resolution LIDAR data becomes available.

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