A 100 tons, 40 m3, rock block struck a former sheepfold transformed into a chalet in the village of Isola in the night on February 23th 2014, in the French Alps of Alpes-Maritimes department. Two children were killed and five other persons were slighty injured. After having passed through the chalet, the block stopped on a road below (NiceMatin).
Seven people, five adults and two children, were asleep when the massive block, measuring 10 m by 5 m, hit the three-storey chalet at about 3:30 am. Three persons could leave the chalet by themselves. At 4:30 am, a mountain rescuer accompanied by a sniffer dog found a man and a woman under the rubble. The lifeless bodies of the two boys, seven and ten years old, were discovered at 7:00 am. Sixty paramedics and mountain rescuers have been deployed on the site. The five adults were transferred into a hospital in Nice where they received psychological support (NiceMatin).
According to G. Marchand, gendarmerie commandant, “the rock felt because the rock face had been weakened by a strong rains period followed by a milder weather” (NiceMatin). Meaning that cracks in the cliff were filled with water relieving the rock.
The geologist A. Faure, who has investigated the site, explains that 100 m3 rock felt from the slope, including a rock block of 50 m3. She explains that rock broke up because of repetitive freeze-thaw actions.
According to the geologist, road clearing and security works will take one week and new expertises are necessary. She explains that it is quite common to find old sheepfold build on rocky slabs in the area. They have been protected from rockfalls by low stone walls. But those stone walls broke down over time (AFP).
The RM 2205 road is closed but a traffic deviation has been set up to allow an access to the ski resort of Auron and villages in the upper Tinée valley. This access is essential because the event occurs during the French winter school holidays which are the busiest time of the year for the Alpine resorts (BBC).
This tragedy occurred fifteen days after the rockfall event on a train in Annot, 37 km away, and five weeks after the rockfall which cut the road 10 km down the valley.
A rockfall occurred on the opposite valley side, 300 m downstream in the early 2000ies. The rocks mass covered a bridge. The Isola area is instable and hazard events occur frequently (Riskpaca). Different studies have already been made in the area, such as the one produced by the Ecole des Mines de Nancy (Gunzburger et al ).
Sources: NiceMatin, BBC , Gunzburger, Soukatchoff
Source: Twitter @btonanny
Source: Twitter @btonanny
Map source: Géoportail IGN
Source: M. Jaboyedoff, unil
Film of the site taken with a drone: Dailymotion
Regional map of rockfall susceptibility: Riskpaca
