Gallivaggio landslide: the geological monitoring, of a rock cliff, for early warning system

Abstract

The Gallivaggio rock cliff, in the San Giacomo Filippo district (Sondrio province, Italy) has been monitored by ARPA, Lombardy’s Geological Monitoring Centre (CMG) since 2011. The main mountain passage, route S.S.36, crosses this mountain area. The village of Gallivaggio was built at the beginning of 17th century and now has a restaurant, some houses and the important sanctuary heritage site. ARPA CMG has carried out a variety of on-site observational approaches to manage the geological monitoring in Gallivaggio during the last few years. The first few years of study and monitoring allowed us to categorize two main conditions. The first, a frequent but less hazardous one which is the single block fall. This is impossible to predict and has a 2-22% possibility of overriding the iron nets. The second one is the collapse of 5-6000 cubic meters of bedrock (Truzzo granite) from the top of the rock cliff which was marked by a large fracture. During the winter of 2017/18 the data analysis values acquired, enabled CMG to notify the Lombardy Region Civil Protection of a dangerous acceleration of movement in the rock area regarding the second scenario. Then, on 13th April, from the identified area single rock blocks began to come down and hit the road and sanctuary. During the following days the houses and restaurant were evacuated and the road was closed for 18 hours a day. Lastly, on May 29th, about 5500 cubic meters of rock collapsed and a part of it covered road and impacted the Sanctuary and the bell tower. In conclusion, it is possible to verify that a suitable monitoring network plan and strategy realised by a reliable remote monitoring system, allowed CMG to alert the Civil Protection and the Municipality during a worsening of landslide movements and demonstrates the utility of an organized management of a monitoring geological network.