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The 1963 Vaiont landslide represented, first of all, a human catastrophe for the many victims caused. Many questions, legal, economic, societal, and scientific have accompanied its history, before and after 9 October 1963. Edoardo Semenza (1927- 2002) was the geologist who discovered, some years before the beginning of the first movements, that an ancient landslide mass was present on the left side of the Vaiont Valley. In this paper, the geological and geomorphological features that led him to define the shape and the boundary of the ancient landslide, are described. Photographs from 1958 to 1963 illustrate both the complex geology of the area and those peculiar features, such as the massive aspects of the rock mass, that hindered to many, the real condition of the slope. A palinspastic reconstruction of the Vaiont slide, starting from the postglacial mass movement and including the 1963 failure, is the last contribute of Edoardo Semenza to the understanding of the event. His work helped to clarify fundamental questions regarding the existence of a paleo-landslide and its connection to the most recent movement. This paper is a personal tribute of the author to her mentor.

The nature of the physical processes that trigger rockslope instability is, today, understood even if with some difficulties and simplifying hypotheses, but the striking mobility of the flow of these rock masses still remain in a large part inexplicable. Three major rock avalanches in the Italian Alps have been studied focusing in particular on aspects relating to the fragmentation and deposition processes. Studies have focused on grain size distribution of samples taken at different distances and elevation and on the morphology of the ground surface of the deposits. Image analysis technique was useful to complete the cumulative grain size curves to include larger particles. In none of the three cases the significant parameters of the grain size distribution and of the particles morphology have shown any relationships with the distance from the centre of the failed mass and with the height of the taken sample over the base of the deposit. The roundness of particles is practically the same within the whole deposits and, even between different deposits for which travel distances and thicknesses are different. The morphology of the three deposits gave some information on the dynamics of the phenomenon and, in particular, on the progressive thinning of the moving debris.

Large slope failures are characteristic of the strongest eruptions of the Kamchatka volcanoes during the last 60 years. Their causes, mechanisms and volumes differ depending on the morphology of the volcanic edifice, type and intensity of eruption, magma composition and viscosity. Rockslides of 0.05 and 0.006 km in volume on high, steep slopes of the Klyuchevskoi volcano during 1945 and 1985 eruptions were caused by deformation of the upper part of the edifice, which swelled due to magma intrusion. The trough-like shapes of scars that narrow downslope are due to destruction of inclined strata of heterogeneous rocks dissected by radial tension fractures. The strata also are affected by permafrost, and contain ice. Giant (>1 km) failure of the andesite extrusive massif of the Young Shiveluch volcano in 1964 was induced by motion of viscous magma below its basement. Such failure is typical of this volcano and has occurred more than 10 times in the past. Catastrophic collapses of the andesite volcanoes Bezymianny and Novyi in 1956 and 1985 were caused by intrusions of large amount of fresh viscous magma into their edifices.

Massive rock failures pose one of the greatest hazards at stratovolcanoes; more than 20,000 fatalities have resulted worldwide from historical volcano edifice collapses. Although numerous processes can destabilize an edifice, gravitational instability is strongly influenced by the interplay of topography, variable potential failure surfaces, and the three-dimensional (3-D) distributions of rock strength and pore-fluid pressure. We have developed a 3-D slope stability analysis that can search digital topography and determine the locations of minimum stability and the volumes of potential failures. We use this 3-D method to conduct preliminary stability analyses of three stratovolcanoes that have had large rock failures: Mount St. Helens and Mount Rainier in the USA and Volcan Casita in Nicaragua. For the relatively uniform Mount St. Helens edifice, a 3-D analysis using topography alone provides a good predictor of the location and volume of the catastrophic 1980 collapse. At Mount Rainier, both topography and a 3-D distribution of weaker, hydrothermally altered rocks are needed to adequately characterize future hazard. For Casita, the location of the smaller, yet devastating, 1998 failure is predicted using topography and a reconnaissance interpretation of strength based on the distribution of fumarolic activity.

Giant volcanic landslides are one of the most hazardous geological processes. On Tenerife, seven large landslides affected the subaerial and submarine morphology during the last ∼6 Ma. A comprehensive analysis of the La Orotava events was carried out including site investigation, laboratory tests and stability analyses. The results revealed that the stability of the volcano can be strongly reduced by geologic, morphologic, climatic and volcanological factors. Widespread residual soils might act as potential slip surfaces, while deep erosive canyons probably evolve into the lateral limits of the failures. A high coastal cliff, humid climate and especially persistent dike intrusion contributed to critical stability conditions. Finally, seismic ground acceleration generated by a strong and adjacent tremor triggered the landslides. On Tenerife, a temporal coincidence of large landslides with caldera collapse events suggests that strong earthquakes associated with caldera collapses may have triggered the failures.

Rock avalanches and related tsunamis represent one of the most serious natural hazards in Norway, and during the last 100 years more than 170 people have lost their lives in western Norway. Large-scale rock-slope failures range from sliding of relatively intact masses of rock, to fully disintegrated rock avalanches. A wide variety of features mirror rock avalanches plunging into valleys or fjords. Bouldery fans, lobes and ridges characterize the proximal parts, while thin debris-flow deposits often occur far beyond this zone. Major deformations of valley-fill and fjord sediments are commonly related to the impact of large volumes of rock. The spatial and temporal pattern of rockavalanche events in Norway demonstrates that such events are common and occur within certain regions, and are important data for evaluating background hazard levels. The mechanisms for occurrence and triggering of rock-slope failures are still uncertain, but seismic ground shaking and creep processes are probably important although, in some areas, effects of glacial unloading during the deglaciation phase cannot be excluded. The geographic concentrations of events indicate that relatively large earthquakes may have played a role as triggering mechanisms. This hypothesis is strengthened by the identification of postglacial faults in two of the rock-failure zones.

In NW Argentina rock avalanching occurs in two geomorphic settings: A) narrow valleys draining large basins and B) mountain fronts bordered by wide piedmont areas. In the narrow valley environment, the deposits are relatively young. Landslide events concentrate during humid climate periods, and they occur with recurrence intervals of a few ka. In contrast, the deposits in piedmont settings are significantly older, while rock avalanches occur with recurrence intervals of several tens ka, and do not show any direct relation with climate change. Common to the regional distribution in both settings is the influence of lithology, structural control, as well as tectonic activity. Rock avalanches have occurred only in granites, low-grade metamorphic rocks and coarse clastic sedimentary rocks. These lithologies are competent enough to form steep slopes and provide planar structures that dip towards the valley. Because all rock-avalanches originated in the hanging wall of reverse faults with important Neogene displacement causing mountain-front oversteepening, it is inferred that most collapses were tectonically conditioned and/or triggered. However, only at a few sites detailed sedimentologic studies of related sediments show unequivocally that strong seismic activity triggered landsliding. Geological evidence and comparison with empirical data suggest that these earthquakes have been either crustal and of magnitude > M 7 or very shallow and of a magnitude > M 5.5.

The paper concerns rock avalanches and their deposits reflecting strong interactions with rugged terrain, deformable and wet substrates. Of 186 rockslide-rock avalanche events identified in the Karakoram Himalaya, over 160 show singularities related to run out in rugged terrain.

Rockslides and rock avalanches in Northern and Central Tien Shan, that have been deeply dissected by subsequent erosion, or which internal structure was studied in trenches and road cuts, are described. Presence of intensively comminuted debris overlaid by coarse blocky material is found out in most of the case studies. At those cases, where different types of parent rocks outcrop in the rockslide scars, the resultant deposits are composed of the unmixed 'layers' of debris originated from these rock types. Such grain size distribution and unmixing of debris can be considered as typical features of large-scale massive rock slope failures. Basal sliding surfaces with different relationships between rockslide debris and underlying soil can be observed at several sites. Comprehensive study of deeply dissected deposits of rockslides and rock avalanches can shed light on mechanism of their rapid motion and of 'rock' → 'debris' transformation.

Landslides play a crucial role in the erosion and topographic evolution of active mountain belts. They drive the expansion of drainage networks in uplifting rock mass, and counter the tectonic mass flux into orogenic systems. Moreover, landslides are the source of most sediment eroded from the continents, and the probability distributions of landslides and their triggers are a first-order control on the variability of the sediment flux from active mountain belts. Here, we illustrate these points with observations from he Southern Alps and other regions of New Zealand, the Central Taiwan Mountains, the Finisterre Mountains of Papua New Guinea and the eastern Greater Caucasus of Azerbaijan.