The relationship between rock-slope failure and glacier retreat is complex, and paraglacial failures often lack clearly identified triggers. To better understand the role of glacier retreat in rock-slope failures, we analysed the processes that led to the October 1967 Grewingk landslide in Kachemak Bay State Park on the Kenai Peninsula, Southcentral Alaska. The rock material collapsed onto the glacier toe and into its pro-glacial lake and produced a tsunami wave that swept the outwash plain. On the day of the failure, rainfall and snowmelt were well within normal ranges, and seismic records show no significant shaking. Three years prior to the 1967 failure, the slope withstood the second largest earthquake ever recorded (Great Alaskan earthquake, M_W 9.2). We reassessed the volume of the failure by differencing pre- and post-digital terrain models and found a value of 20–24 × 10⁶ m³, which is four times smaller than a previous estimate. The back analysis of the Grewingk landslide is based on remote sensing data and field measurements including aerial satellite image analysis, detailed surveying and understanding of the structural geology, a kinematic analysis, and runout modelling. Our research provides an example of a major paraglacial failure that lacks an obvious trigger and points to several geological factors and changing environmental conditions that likely promote such failures. This study further indicates that the Grewingk landslide, pre-conditioned by the geometry of faults and joints, may have reached a critical stability state due to internal processes and the potential combined effects of seismic activity and glacier retreat prior to the collapse.

The stability of rock slopes is often guided significantly by the structural geology of the rocks composing the slope. In this work, we analysed the influences of structural characteristics, and of their seismic responses, on large and deep-seated rock slope failure development. The study was focused on the Tamins and Fernpass rockslides in the European Alps and on the Balta and Eagle’s Lake rockslides in the southeastern Carpathians. These case studies were compared with catastrophic rock slope failures with ascertained or very likely seismic origin in the Tien Shan Mountains. The main goals was to identify indicators for seismically-induced rock slope failures based on the source zone rock structures and failure scar geometry. We present examples of failures in anti-dip slopes and along-strike rock structures that were potentially (or partially) caused by seismic triggering, and we also considered a series of mixed structural types, which are more difficult to interpret conclusively. Our morpho-structural study was supported by distinct element numerical modelling that showed that seismic shaking typically induces deep-seated deformation in initially “stable” rock slopes. In addition, for failures partially triggered by dynamic shaking, these studies can help identify the contribution of the seismic factor to slope instability. The identification of the partial seismic origin on the basis of the dynamic response of rock structures can be particularly interesting for case histories in less seismically active mountain regions (in comparison with the Andes, Tien Shan, Pamirs), such as in the European Alps and the Carpathian Mountains.

Slope instability poses significant challenges in geotechnical engineering, necessitating effective mitigation strategies. Among these strategies, toe buttressing has emerged as a prominent method, involving the strategic placement of materials at the base of unstable slopes. However, the efficacy of toe buttressing remains insufficiently explored in scientific literature, particularly through the integration of real-time monitoring and numerical modeling. This paper explores the effectiveness of toe buttressing as mitigation measure for slope stability without the influence of additional stabilization methods. Through a combination of field monitoring, laboratory testing, and the finite element analysis, we assess the influence of toe buttressing on slope dynamics and stability under varying environmental conditions. The study site, located in a basalt quarry in Nentershausen, Germany, experienced a landslide, with the sliding plane located at the interface between basalt formations and the underlying clay layers. Our monitoring results demonstrate that the placement of a 10 m thick toe buttress effectively halted the movement of a 295,000 m³ landslide. Additionally, we investigated the impact of different buttress configurations and groundwater levels on the factor of safety (FoS) using a 2D finite element model. The results clearly show the important role that toe buttresses play in strengthening slope stability. Our study emphasizes the need for more detailed case studies focusing solely on toe buttressing as a means of stabilization. Such research is essential to develop statistical models that can determine the necessary buttress volume and height to support/stabilize different landslide scenarios. Additionally, we discuss the broader implications of our study and future research for slope management applications and underscore the need for interdisciplinary approaches to address the complexities of slope stability in a changing environment.

Paraglacial landscapes are rapidly transforming as thinning and retreating glaciers expose adjacent slopes to new conditions. In Southcentral Alaska, a large slope instability at Portage Glacier has been deforming progressively up‐glacier over the past six decades. The instability comprises two deep‐seated rock slope segments, Portage A and Portage B, located above the thinning and retreating Portage Glacier and its proglacial lake. Portage B lies at the glacier terminus, while the down‐glacier margin of Portage A is about 300 m further up‐glacier. To understand the mechanisms driving slope deformation, we integrated field observations, historical imagery, structural and kinematic analysis, differential DEMs, InSAR, and coherence radar to capture both short‐ and long‐term deformation patterns. We identified three distinct domains of movement: two in Portage A and one in Portage B. Our findings reveal that Portage A experiences rapid and variable displacement rates, whereas Portage B shows slower motion. Structural analysis indicates translational sliding and toppling as primary failure mechanisms controlled by pre‐existing geological discontinuities. Glacier thinning is identified as a key factor, initiating movement and enabling the progressive spatial up‐glacier propagation of deformation from Portage B to Portage A. But this process is not solely driven by thinning; rather, it reflects how ice loss progressively alters mechanical boundary conditions, granting kinematic freedom for the rock mass to deform along pre‐existing structural discontinuities. Consequently, our results underscore the importance of considering both glacier thickness thresholds and structural geology to better understand and assess the onset and evolution of slope deformation in paraglacial environments.

As glaciers thin and retreat worldwide, the stability of surrounding rock slopes is increasingly at risk. This study investigates the long-term deformation of two major on-going instabilities, Portage A and Portage B, situated above Portage Glacier in Alaska. By analyzing decades of historical imagery and remote sensing data, we reconstructed the spatial evolution of these slopes, revealing progressive deformation up-glacier over the past sixty years. To further assess the links between glacier change and slope deformation, we combine structural mapping with remote sensing observations and kinematic analyses. Our results identify three distinct kinematic domains and show that progressive deformation is initiated once the glacier surface lowered below a critical elevation. This creates kinematic freedom for the rock mass to move along structural discontinuities. At Portage Glacier, the onset and progression of the instabilities are not governed solely by glacier thinning but reflect a complex, site-specific interaction between structural discontinuities and cumulative weakening from external processes. Glacier retreat and thinning act as one component within a broader “cascade system”, where multiple factors interact. Additionally, preliminary results from our three-dimensional model provide additional insights into the mechanical response of the slopes under changing boundary conditions. These findings highlight the importance of integrating structural, kinematic, and remote sensing data to better understand paraglacial slope dynamics and anticipate future instabilities in rapidly deglaciating mountain regions.

The characterisation of tuffaceous soft rocks represents a substantial challenge for slope stability evaluation. The geomechanical behaviour of these materials depends heavily on the microheterogeneity of pyroclastic rocks and varies considerably based on the degree of alteration and water-rock interaction processes.Tuffaceous lithologies outcrop in a wide variety of areas worldwide, often forming landslide-prone vertical cliffs, both in coastal and continental settings. These instability processes are controlled by progressive rock failure (PRF) mechanisms that govern the enucleation and propagation of fractures, the evolution of which can lead the slope to a state of instability. PRF process can be numerically analysed by adopting hybrid stress-strain numerical solutions able to capture the transition from continuum to discontinuum behaviour. However, these tools require micromechanical input parameters governing the fracture mechanics (e.g., fracture toughness/energy), which are often difficult to calibrate numerically.This study focuses on the tuffaceous cliffs of Ventotene Island (Italy), highly susceptible to rock-falls and topples and exposed to sea-wave actions, combining laboratory testing and numerical modelling. In the site the mechanisms of progressive fracturing in this type of soft rock and its relationship with environmental forcings are deepened through the design and implementation of the “Ventotene Field Laboratory”. This natural field laboratory, part of EPOS Field-Scale Laboratories, allows the integration of field observation, in situ monitoring data and numerical investigations.To characterise the mechanical behaviour of the Ventotene tuffs, uniaxial compressive strength (UCS), indirect tensile (Brazilian) and fracture toughness (FT) tests were performed at Aachen Rock Mechanics Laboratory on representative rock samples under both dry and saturated conditions. The laboratory results highlight a strong influence of water content on the mechanical properties of the tuff, with a marked reduction in strength and stiffness under wet conditions. In addition, the thermal properties of the material were also investigated to support thermo-mechanical analyses.The laboratory test results were used to provide (micro)mechanical input parameters to a FDEM slope numerical model using the Irazu software (Geomechanica Inc.). Overall, the results show that numerical calibration is essential to obtain a tuned parametrisation of tuffaceous soft rocks and to bridge the gap between laboratory-scale measurements and field-scale responses.The laboratory tests were numerically simulated, and the calibrated parameters have been transferred to a numerical domain representative of the Ventotene sea cliffs. This latter model served to perform accurate slope stability analysis of coastal cliffs, by combining the action of different (marine and environmental) controlling factors.The calibrated micromechanical parameters also provide a robust basis for future modelling FDEM studies since calibrations of this nature have rarely been conducted on tuffaceous lithologies.