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The characterization of landslides located in remote areas poses significant challenges due to the costs of reaching the sites and the lack of reliable subsurface data to constrain geological interpretations. In this paper, the advantages of combining field and remote sensing techniques to investigate the deformation and stability of rock slopes are demonstrated. The characterization of the Fels landslide, a large, slowly deforming rock slope in central Alaska, is described. Historical aerial imagery is used to highlight the relationship between glacier retreat and developing instability. Airborne laser scanning (ALS) and Structure-from-Motion (SfM) datasets are used to investigate the structural geological setting of the landslide, revealing a good agreement between structural discontinuities at the outcrop and slope scales. The magnitude, plunge, and direction of slope surface displacements and their changes over time are studied using a multi-temporal synthetic aperture radar speckle-tracking (SAR ST) dataset. The analyses show an increase in displacement rates (i.e., an acceleration of the movement) between 2010 and 2020. Significant spatial variations of displacement direction and plunge are noted and correlated with the morphology of the failure surface reconstructed using the vector inclination method (VIM). In particular, steeper displacement vectors were reconstructed in the upper slope, compared to the central part, thus suggesting a change in basal surface morphology, which is largely controlled by rock mass foliation. Through this analytical approach, the Fels landslide is shown to be a slow-moving, compound rockslide, the displacement of which is controlled by structural geological features and promoted by glacier retreat. [ABSTRACT FROM AUTHOR]

Landslides are among the most common type of hazard that affect mountainous regions. While the impact of the single landslide is often localized and limited to the influence area, in some cases, the occurrence of major events can result in significant and long-lasting social, economic, and environmental impacts that extend beyond the area directly affected by the event. These major landslides involve the sudden detachment of large volumes of rock mass and cause significant disturbance of in-situ stress field due to slope debuttressing and reduction in lateral support, which often result in conditions of limit equilibrium affecting the remaining part of the slope. Effects of such limit equilibrium conditions can range from a long term, gradual morphological evolution of the slope due to progressive detachment of material, to the development of multistage landslides, involving the failure of volumes of rock mass similar in magnitude and impacts to the original event. In this work, we investigate the post-failure morphological evolution of the daylighting rupture surface and deposit of one of the most important historical landslides, the 1963 Vajont Slide. A preliminary investigation of a pair of airborne laser scanner (ALS) datasets, collected in 2017 and 2023, is undertaken to assess and compute the change in elevation across selected areas within the rupture surface. Based on a three-dimensional change detection analysis, the observed volumetric changes of selected, inferred rockfall events are estimated. Terrestrial and airborne photographs are also used to identify the unstable volumes that have progressively detached, as well as the damage features that outlined these unstable blocks. Finally, we discuss the long-term evolution of the slope with focus on progressive damage accumulation and its spatial relationship with inherited, tectonic structures. Ultimately, this contribution is intended to highlight the important role of post-slope failure damage accumulation on the long-term stability of rock slopes, emphasizing the critical role that post-failure monitoring and analysis can play in outlining the residual landslide hazard and, in some instances, the potential development of multi-stage landslides. [ABSTRACT FROM AUTHOR]