This work concerns a proposal of the integration of InSAR (Interferometric Synthetic Aperture Radar) data acquired by ground-based (GB) and satellite platforms. The selected test site is the Åknes rockslide, which affects the western Norwegian coast. The availability of GB-InSAR and satellite InSAR data and the accessibility of a wide literature make the landslide suitable for testing the proposed procedure. The first step consists of the organization of a geodatabase, performed in the GIS environment, containing all of the available data. The second step concerns the analysis of satellite and GB-InSAR data, separately. Two datasets, acquired by RADARSAT-2 (related to a period between October 2008 and August 2013) and by a combination of TerraSAR-X and TanDEM-X (acquired between July 2010 and October 2012), both of them in ascending orbit, processed applying SBAS (Small BAseline Subset) method, are available. GB-InSAR data related to five different campaigns of measurements, referred to the summer seasons of 2006, 2008, 2009, 2010 and 2012, are available, as well. The third step relies on data integration, performed firstly from a qualitative point of view and later from a semi-quantitative point of view. The results of the proposed procedure have been validated by comparing them to GPS (Global Positioning System) data. The proposed procedure allowed us to better define landslide sectors in terms of different ranges of displacements. From a qualitative point of view, stable and unstable areas have been distinguished. In the sector concerning movement, two different sectors have been defined thanks to the results of the semi-quantitative integration step: the first sector, concerning displacement values higher than 10 mm, and the 2nd sector, where the displacements did not exceed a 10-mm value of displacement in the analyzed period.

On September 5, 2019, the Veslemannen unstable rock slope (54,000 m³) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

In 2023, a 54,000 m ³ large rock section failed catastrophically from the unstable rock slope Stampa (Western Norway). The failure occurred in a multistage process with two major failure events on July 1 ^st and 3 ^rd . In this study, we present a detailed analysis of the pre-failure displacement patterns, the failure mechanisms, and failure events. After exponential acceleration, the base (12,200 m ³ ) of the rock section failed, leading to a further destabilization of the remaining rock column (41,800 m ³ ), which failed 2 days later. The monitoring data includes in situ displacement sensors, a robotic total station, and close range and remote sensing data spanning over 14 years. The rock section showed seasonal displacement patterns clearly influenced by meteorological factors: (1) late spring (May–July) accelerations, controlled by positive temperatures, thawing ground, and meltwater infiltration, followed by (2) summer stabilizations characterized by low displacement, and (3) autumn (October–November) accelerations driven by precipitation events over a longer period, followed by (4) winter stabilizations approaching zero displacement. The deformation rates increased from 0.06 m a ⁻¹ in 1991–2019 more than a tenfold to 0.78 m a ⁻¹ in 2022 and indicate progressive damage and weakening of the rock section, which increased its sensitivity to rainfall and infiltration. Our findings highlight the importance of long-term, high-resolution monitoring using different, independent sensors, alongside detailed failure analyses, in understanding the evolution of unstable rock slopes. This study contributes to the understanding of progressive medium-scale rock slope failures, aiding in the prediction and mitigation of potential failures.