The Cercevesa Valley landslide in Friuli Venezia Giulia, Italy

The Cercevesa Valley landslide, located in Paularo, Friuli Venezia Giulia at an altitude of 1100-1600 m, is one of the fastest largescale mass movements in rock slope currently active along the Alps. The mountainside is characterized by a sequence of Devonian tentaculata limestones overlying Hockwipfel Formation sandstones. Landslides movements started in 1990-1992 and the most evident morphological feature was the opening of a crestal trench that has an actual offset of 20 m and a total length of 600 m. Nowdays the features is clearly identifiable from satellite viewers. Since 2011 many small rockfalls occured rolling over the steep slope towards the Cercevesa River. The Friuli Venezia Giulia Geological Survey started monitoring the area from 2008; spreading trench measures have been acquired in nine different sites by laser distance meter and three GPS benchmarks have been installed by Univ. Trieste and OGS. Several photogrammetric flights and one helicopter laser scan acquisition have been compared: the average movement rate is about 80 cm/year. The trench reveals a higly consistency opening rate with linear correlation coefficient r= 0.998-1.000. Kinematics is not sensitive to seasonel changes: rain, snowmelt and the freezing of the ground surface that in the area reduces water infiltration. There have been considered several different triggering factors in time span 1990-1992: the 1990 mid-november rainfall was the only relevant one. It also has been analysed how the effect of the last century snow level reduction, occurred during Autumn’s months, can have helped the triggering factor.