5.1.3 Details on consequences of the slide process

Contrary to fall events, slide events are in most cases slow phenomenon. Thus, human losses caused by slides are exceptional, but possible (figures 2 to 5). Damages to buildings are frequent, from simple cracking to total ruin. Slides can also cause interruption of roadway systems. According to the extent of the slide phenomenon, damaged area is more or less important.

Figure 1: Different effects of a slide event on a house (modified from Léone and al., 1996
Figure 2: House damaged by the landslide of La Salle en Beaumont, near Grenoble, France, on January 8 1994.

Because of very heavy rainfalls during 2 consecutive days, a 1,3 millions m3 slide triggered during the night. First a crown appeared and destroyed a house. Then a 15-meters-thick slide advanced into the gorge of a stream. Finally, 9 houses were damaged and 4 people were killed while they were sleeping (from www.irma-grenoble.com)

In 1985, in Puerto Rico, a 300,000 m3 rock-block-slide destroyed 120 houses and killed 129 people at least. This landslide was caused by extraordinarily heavy rainfalls during 24 hours. The landslide failed in 3 distinct phases between 3:00 and 4: am on October 7 1985. The first two phases involved 12 meters-thick translational slides. The third phase involved the toppling failure of a block that disaggregated and form a rock fall on the western part of the slide. Subsidiary flow failures onto the toe and from the downstream face of the toe were triggered by the heavy rainfalls and the rupture of a water pipe that emptied as much as 4 million litres of water onto the slide (Figures 3 to 5).

Figure 3: Disrupted area above the toe of the landslide. House debris are visible on the surface (from Slosson and al., 1992)
Figure 4: Oblique aerial photograph of the landslide toe (from Slosson and al., 1992)
Figure 5: Photograph showing cracks in ground surface on second main landslide block (from Slosson and al., 1992)
Figure 6: Road cut off by a translational slide in Merlas, Isère, France, on June 6 2004 (from www.irma-grenoble.com)
Figure 7: Translational slide in a highway slope, Voiron, Isère, France, on November 18 2002 (from www.irma-grenoble.com)
Figure 8: Building damaged by a rotational slide in Vilnius, Lithuania (from Malet, 2003)
Figure 9: Houses damaged by the rotational slide of La Conchita, Californie, USA (from Malet, 2003)
Figure 10: Truck knocked down by a slide in front of a residential area, France (from MATE, METL, 1999)
Figure 11: Bridge destroyed by an earth flow in 1968 in the River Panaro valley (photo by M. Pellegrini)

References:

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
MALET J.P. Les « glissement de type écoulement » dans les marnes noires des Alpes du sud. Morphologie, fonctionnement et modélisation hydromécanique. PhD Thesis: Institut de Physique du Globe, Université Louis Pasteur de Strasbourg, 2003. 353 p.
MATE, METL, 1999. Plans de prévention des risques naturels prévisibles (PPR) : Risques de mouvements de terrain. Guide général. La Documentation française, Paris, 71 p.
SLOSSON E., KEENE A.G., JOHNSON J.A., 1992. Landslides/Landslide mitigation. In: Reviews of Engineering Geology, Volume IX, Colorado

Websites:
www.irma-grenoble.com
www.prim.net

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