5.1.4 Details on consequences of the fall process

Because of their sudden and (in many cases) unpredictable nature, fall events can be very dangerous for the infrastructures and the population.

Damages extent depends on energy of the falling material (function of weight and velocity). Rock falls can damage housing, interrupt roadway systems and cause human losses.

Fig. 1: Different effects of a fall event on a house (modified from Léone and al., 1996)
Fig. 2: House damaged by a block fall, Norway (from www.ngi.no)
Fig. 3: Buildings on the train station quay damaged by Aigueblanche rockfall, Savoie, France, in 1977 (from Besson, 2005)
Fig. 4: House and car damaged by a 30 ton block fallen in Lumbin, Isère, France, on January 2 2002 (from www.irma-grenoble.com)
Fig. 5: Road damaged by a 2000 m3 rock fall, Saint-Quentin-sur-Isère, France (from www.irma-grenoble.com)
Fig. 6: Road damaged by a rock fall, Laffrey, Isère, France (from www.irma-grenoble.com)
Fig. 7: Rock fall near Choranche, Isère, France, on January 31 2004: 2000 m3 rock falled on a departmental road. A car has been ran down, the two passengers have been killed (from www.geolithe.com)
Fig. 8: Rock fall on the same road than in fig. 15, on November 2 2007 : 5 m3 rock landed on a car and killed two of the five passengers of the vehicle (from rhone-alpes-auvergne.france3.fr)

Fig. 9: Car damaged by a rock fall at Upper Island Cove, Canada, on February 14 1999. A 8 ton block toppled from the top of a 100 m slope, ran roughly 150 m, struck a house, and landed on the top of a car parked beside the house (from www.heritage.nf.ca)

Constructive layouts exist to protect housing, such as reinforcement of the exposed façade or the roof. But the best way is to avoid building in vulnerable areas and to use protection techniques.

Consequences of the rockfall avalanche process

Rock fall avalanches are incredibly destructive, they move with great rapidity and obliterate everything in their path. Perhaps the most important, once an event has occurred, is to discover whether the avalanche has dammed the valley. If it has, and a lake has formed, maximum effort must be given to take control of the breaching dam, because the resulting flow may cause a second disaster.

Consequences of the topple process

Topples are potentially very dangerous because they develop at first by loading, then by progressive basal failure and rotation, and eventually sudden collapse. This failure is dramatic, the break-up spectacular and the velocity of loose boulders and run-out high.

Damages on the infrastructures and population are the same than concerning fall risk (see details on fall).

BESSON L., 2005. Les risques naturels: de la connaissance pratique à la gestion administrative. Editions Techni. Cités, Voiron, 60 p.
LEONE F., ASTE JP., LEROI E., 1996. Vulnerability assessment of elements exposed to mass movements: working toward a better risk perception. In: Senesset K (Ed): Landslides, Proceedings of the 7th International Symposium on landslides, Balkema, Rotterdam


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