An extended kinematic inventory, magnitude-frequency curves, and damage assessment of rock slope failures in the central Spanish Pyrenees

A new inventory of rock slope failures (RSFs) compiled in the central Spanish Pyrenees within the framework of the SPIRAL Project has identified 1232 RSFs, yielding a relatively low spatial density of 0.11 events per km 2 . These RSFs exhibit very slow to extremely slow average displacement rates, ranging from 5 mm to 75 mm per year. Rock slides and earthflows are the most prevalent failure types, accounting for over 93% of the total, whereas rock slope deformations (RSDs), composite failures, and rock avalanches are comparatively rare. This predominance of rock slides and earthflows results in a shallower magnitude–frequency distribution relative to other mountainous regions. Lithology, glacial debuttressing, and slope angle are identified as the most influential conditioning factors. Most RSFs occur on slopes between 20° and 30°, especially in deglaciated settings and in bedrock composed of fine-grained, low-strength lithologies, such as turbidites, slates, marls, and evaporitic sequences, where weathering plays a critical role in promoting slope instability. Unfortunately, these relatively moderate slopes, which often correspond to relict landslide deposits, provided favourable conditions for the establishment of at least 25 human settlements in the past. These communities are now under threat and will require multimillion-euro investments to stabilize active movements. Furthermore, 41 RSFs intersect communication and irrigation networks, 138 affect ski resort infrastructures, 94 compromise paved roads, and 29 pose risks to dam safety. The estimated direct costs associated with active RSFs already exceed €152 million, and additional substantial mitigation efforts are anticipated in the near future. • 1,232 rock slope failures were identified, a 1,000% increase over the previous national dataset. • Slope gradient and aspect, glacial unloading and lithology control the spatial distribution and typology of rock slope failures. • The slope of earthflows differs significantly from the adjacent undisturbed terrain. • Pyrenean rock slope failures show higher frequency of small events than UK or Alps. • Magnitude-frequency trends for rock slope deformations and composite failures in the Pyrenees match Alps and UK patterns. • Direct economic losses from rock slope failures exceed €152 M over the past 20 years.