Réf. Hantz 2007 - C1

Date
Titre
Auteur(s)
19/02/2007
Rock falls and triggering factors
Didier Hantz

Mots-clés
Rock falls, triggering factors, freeze/defreeze cycles, precipitations.

Organisme(s) / Contact(s)
Laboratoire de Géophysique Interne et de Tectonophysique, LGIT - BP 53, 38041 Grenoble Cedex 9 ; Tel. : (+33)  476.82.80.40 ; Fax : (+33) 476.82.81.01.

Références des études sur lesquelles porte le commentaire
Frayssines M. and Hantz D. 2006. Failure mechanisms and triggering factors in calcareous cliffs of the Subalpine Ranges (French Alps). Engineering Geology 86, 256-270.
Matsuoka N. and Sakai H. 1999. Rockfall activity from an alpine cliff during thawing period. Geomorphology 28:309–328.

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
    Mass movements Rock Falls

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période d'observation
France, Japan French Subalpine Ranges, Hosozawa Cirque     200-1600 m asl 1970-2004

Commentaire

A statistical analysis of the influence of climatic factors on 46 rock falls occurred between 1970 and 2004, at elevations between 200 m and 1600 m, and with volumes ranging from 10 to 30,000 m3, has been performed. No significant correlation appears between rock falls and rainfall. On the contrary, a significant correlation appears between rock falls and the freeze-thaw cycles: the rock fall frequency is about 2.5 higher a day with freeze and thaw than a day without freeze and thaw. It ensues that an increase of the mean annual temperature should induce a decrease of the number of freeze-thaw cycles at this elevation and then a decrease of the rock fall frequency (for this type of rock falls). On the contrary, at a higher elevation, where the number of freeze-thaw cycles will increase, one can expect an increase of the rock fall frequency (Comment on Frayssines et Hantz 2006).

An analysis of the rock fall activity in the Hosozawa Cirque, Japan, concluded that the intense activity does not reflect precipitation events. Nevertheless, the activity reaches its maximum in May–June, i.e. 5–15 days after the melt out of the cirque wall, which undergoes a deep frost penetration in winter. A thermal conduction model suggests that a lag of 5–15 days would represent thaw penetration to a depth of about 1 m. The authors concluded that the primary factor controlling rock falls is seasonal frost weathering (Comment on Matsuoka and Sakai 1999).