The stability of a rock slope is influenced by a combination of inherent characteristics, including its geometry, geological composition, and structural features, along with external factors such as glacier retreat, seismic activity, climatic forces, and human activities. Key elements in determining overall stability are the conditions and processes occurring at the slope toe and its surrounding environment. In this thesis, a combination of field and remote sensing methods is used to enhance our understanding of the mechanisms at the toe of the slope that influence stability. The research adopts a multidisciplinary approach by investigating four case studies where changes at the slope toe, driven by various processes, influence stability in different environmental settings. Understanding these processes is essential for mitigating risks to human safety, infrastructure, and the surrounding environment, especially in the context of changing climate. One of the topics that gained significant attention in the scientific community over the past decades is the impact of glacier retreat on rock slope stability. This interest arises from the fact that paraglacial failures often occur without clearly identifiable triggers and exhibit diverse timings and mechanisms of failure, making it challenging to understand the direct link with glacier retreat. A key concept in this context is glacier debuttressing. The reduction in support provided by the mass of a glacier as it retreats leads to stress changes on adjacent slopes, potentially driving instability. To better understand this complex phenomenon, this thesis focuses first on investigating two case studies, located in Southcentral Alaska at Grewingk Glacier and Portage Glacier. Both studies focus on the impact of glacier changes on the stability of surrounding rock slopes. The slope at Grewingk Glacier failed in1967 as the glacier terminus retreated beyond the collapsed zone, with no clear triggering event identified. Three years before the 1967 collapse, the slope endured the second most powerful earthquake ever recorded, the Great Alaskan earthquake (MW 9.2). For the case at Portage Glacier, the slope is currently moving above the retreating and thinning glacier and its proglacial lake. The instability has been progressively deforming up-glacier over time, with two main instabilities, Portage A and Portage B. By integrating multi-temporal and multi-disciplinary analysis, these case studies demonstrate that glacier retreat and thinning are part of a network of interconnected processes, generating a “cascading effect” in which each factor can activate or reinforces the influence of others. The focus of the thesis then shifts to a different environmental context, exploring the case of the Civita di Bagnoregio plateau in central Italy that has experienced significant morphological changes and slope instabilities over the past centuries. This study examines the recent slope dynamics using a comparative analysis of 3D high-resolution data from 2016 and 2023. Erosion and weathering processes undermine the weak clay layer at the base of the slope, triggering earth slides and flows within clay deposits. This effect is particularly pronounced in the northern section of the plateau, where a historical landslide redirected a river, causing increased slope steepening and exacerbated erosion, accelerating the degradation process. These mass movements subsequently destabilize the overlying tuff and ignimbrite layers, initiating rock falls that progressively contribute to the plateau retreat, posing a major risk to the town. The findings of this study provide valuable insights into the spatial and temporal changes in slope stability, focusing on the size, distribution, and failure mechanisms of instability events across the plateau. Additionally, the thesis explores the contrasting concept of toe buttressing in slope stability. This chapter investigates a case study from a basalt quarry in Germany, where the toe buttressing method was successfully employed to halt slope movement. Although toe buttressing is a well-known technique, its effectiveness remains underexplored in scientific literature. The monitoring results of this research show that the installation of a 10-m-thick toe buttress effectively stopped the movement of a 295,000 m3 landslide. The impact of different buttress configurations and groundwater levels on the factor of safety was also analyzed using a 2D finite element model. The results emphasize the direct role of toe buttresses in improving slope stability. Moreover, the study discusses the link to broader implications of changes at the toe of a slope, such as those caused by glacier retreat and river erosion. This thesis provides a framework for understanding the complex interactions between slope toe-related processes and rock slope stability. Through a multidisciplinary approach, it provides new insights into how changing processes at the slope toe and structural discontinuities contribute to slope (de)stabilization. This research also draws connections between natural and engineered processes that destabilize or stabilize slopes, by analyzing rock slope stability in the context of changing environmental conditions.
Emilie Lemaire (Wed,) studied this question.