In this paper a review and comparison of new data gathered from the monitoring of thre large landslides in the Swiss Alps are presented, which show a very distinctive mechanism during major reactivation phases. Some comments on the perceptible previous warning signs, which have not always been understood as such, are also helpful in the perspective of future similar situations, when it is of
... [Show full abstract] utmost importance to distinguish them from normal indices of active movements. These three landslides are: Randa rockfall, a large complex rockfall mechanism which occurred in three stages in April-May 1991, in the Matter Valley leading to the touristic resort of Zermatt (Penninic Alps, Canton of Wallis), and implied a total volume of some 30 mio m3. La Frasse landslide, a large continuously moving slide in the Ormonts Valley leading to the touristic resorts of Leysin and Les Diablerets (Prealps of Canton of Vaud), on which specific acceleration phases were monitored in 1966, 1981-82 and since 1993. The total volume of the moving mass exceeds 60 mio m3. Falli-Holli landslide, a gently sloping slide near the town of Freiburg (Prealps of Canton of Freiburg) which experienced in 1994 a long critical acceleration phase with maximum velocities of 6 to 9 m/day and a total displacement of more than 200 m in its most mobile parts. The total volume of the sliding mass is assessed to be some 40 mio m3. -from Authors
