5. What are the consequences of landslides?

Landslide hazard is generally neglected (at global scale) with respect to other types of hazards such as seismic and volcanic hazards, as it is mostly an occasional phenomenon, of low amplitude and limited effects. But some landslides can cause extensive and costly damage because of their diversity, their frequency and their wide geographic distribution. These consequences could be:

  • direct (i.e. building or road damages);
  • indirect (i.e. perturbations, disruptions of railway, road traffic) with long-term economic losses after the event.

Actually, besides high-magnitude mass movements which occur quite seldom, there is a huge number of medium to small sized landslides which are so widespread that the related cost for human society is even higher than that of catastrophic events.

Fig. 1. The train derailed in a landslide occurred on 12/04/2010 near Merano (Alto Adige, Northern Italy) (photo by http://www.ansa.it/)11

Nine passengers died and 28 were injured, seven of which hospitalized after a landslide hit a small, two carriage diesel train, travelling on the Val Venosta line between the Adige river and mountains. The train was filled with local commuters and students. The mass movement was a surficial landslide caused by water infiltration; in fact, it was caused as a pipe in an underground irrigation system burst in an apple orchard. Due to the breakage of the pipe, water infiltrated the soil, rendering it so unstable that it began to slip. The landslide was about ten metres away and smashed into the train as it was passing. There was a line of trees which saved the train from falling into the river Adige and it prevented the passengers from a greater disaster.

Increasing losses due to low-magnitude, high-frequency events are fostered by human activity which tends to increase landslide hazard (e.g. road cuts, quarries) and favours vulnerability situations. Furthermore, a considerable proportion of damage and casualties generally related to earthquakes and volcanic eruptions is due to landslides occurring as an effect induced by these phenomena.

Fig.2: The destructive failure at Holbeck hall (Hotel) in Scarborough, Yorkshire, UK (1992) (Photo by R.Moore)

Go to 5.1 More information on consequences of landslides

Landslides consequences are generally lower  compared to other types of hazards, such as seismic and volcanic hazards, as they are mostly occasional phenomena, of low amplitude and limited effects.
But some landslides cause extensive and costly damage because of their diversity, their frequency and their wide geographic distribution. These consequences could be direct (i.e. building or road damages) or indirect (i.e. perturbations, disruptions of railway, road traffic …) with economic losses during long time after the event.
Historically, one of the major landslides disasters in Europe occurred in France in 1248 when a rock fall at the Mont Granier (Savoy) destroyed 5 villages killing 2000 to 5000 people.

more details on that event >> http://www.ccsti-chambery.org/index_dos.htm (in french).

But other major disasters have caused damage and cost lives in Europe during the last decades:
• Belgium 1958: Rapid subsidence of ancient subterranean quarry at Roosburg; 18 victims;
• France 1961: Rapid subsidence in Clamart & Issy-les-Moulineaux; 21 victims;
 
more details on that event >> http://clamart.cyberkata.org/ (in french)

• Belgium 1961: Flow of Jupille; 11 victims and 17 houses destroyed;
• Italy 1963: Rockslide of Vajont dam; 1909 victims
 
more details on that event >> Go to 13.1.Vajont Case Study

• France 1970: Mudflow of Assy plateau (Hte-Savoie); destruction of a sanatorium, 72 victims;
• France 1994: Slide, Salle-en-Beaumont (Isère), 4 victims,
• Italy 1998: Mudflows of Sarno (Campania); 160 victims, 115 people injured and 1210 became homeless

more details on that event >> Go to 13.2.Sarno Case Study

Actually, besides high-magnitude mass movements which occur quite seldom, there is a huge number of medium to small sized landslides which are so widespread that the related cost for human society is even higher than that of catastrophic events. Increasing losses due to low-magnitude, high-frequency events are fostered by human activity which tends to increase landslide hazard (road cuts, quarries etc.) and favours vulnerability situations.
Furthermore, a considerable proportion of damage and casualties generally related to earthquakes and volcanic eruptions is due to landslides occurring as an effect induced by these phenomena.

Go to More details on different landslides types consequences:
5.1.1. Sinking consequences
5.1.2 Shrinking and swelling consequences (e.g. in France)
5.1.3 Slide consequences
5.1.4 Fall (rockfall avalanche, topple) consequences
5.1.5 Flow consequences

Go to 5. What could be the consequences of LANDSLIDES?

Sinking is a very slow process of vertical deformation with a limited extent (like limited progressive subsidence). The differential deformations can be caused by:

  • The natural consolidation of recent soil formations (Quaternary), under load (weight of overlying grounds and additional weight of constructions). Typical examples for constructional problems/damage due to sinking are the Towers of Pisa and Bologna (Italy), and the Church Saint-Jean in Caen (France);
  • The lowering of groundwater table by pumping. Typical examples are the cities Mexico, Venice, and Bangkok;
  • The exploitation of fluids (like oil in California) or gas (in the Plain of the Po) in soil and rocks.
  • The alternation of humidification and desiccation cycles in clayey soils (e.g. shrinking and swelling);
  • The modification of the stresses in granular soils (liquefiable sands).
Fig.1.Differential sinking beneath the foundation of the Tower of Bologna (Italy) (Photo: Maquaire, Cerg)
Fig.2.Differential sinking affecting the Tower of Pisa (Photo: Castaldini, Cerg).
Fig.3.Topple and deformation of the Saint-Jean Church (Caen, France) due to a major sinking underneath its foundations. The church has been built in the XVth century in a marshy zone of the alluvial plain of the Orne River and is constructed on oak piles. As sinking has appeared during the construction phase, the high of the tower has been limited to reduce its total weight and to decrease the toppling force. (Photo: Maquaire, Cerg).

Shrinking and swelling of clayey soils constitutes a natural hazard, which is indeed less spectacular than sudden and rapid landslides. However, prolonged dry conditions have caused an intense desiccation of sensitive clayey soils. The desiccation cracks reached depths of up to two meters. Subsequent soil compression was induced by an increase in soil moisture during the wet seasons, and finally swelling of the underground. In many regions, these vertical movements have generated high damage to buildings, in particular to small single, individual houses. In France, in the period between 1989 and 1992, the amount of damages was more than 2 billions of Euros. At the end of the year 2002, the total amount of refundings carried out was evaluated to approximately 3,3 billion euros, which corresponds to several hundreds of thousands of damaged houses on the whole of France since 1989.

Cracks caused by shrinking of clayey soils in the Centre of France (Orléans region). In this specific case, the amplitude of the cracks is increased due to the presence of trees inducing root suction (differential sinking) (Photo: Maquaire, CERG)

Factors enforcing shrinking and swelling consequences

Differential compression can be amplified locally by tree or bush suction or by soil heterogeneity (in example, house partially located on sensitive clayey soils and on insensitive formation, e.g. limestone). This causes cracks and damage on bulding structures, and sometimes even the complete destruction of houses.

Shrinking-swelling process

Is there a specific house type which is especially vulnerable to this hazard?
The damage has often pinpointed certain deficiencies in constructions: insufficient depths of the foundations, and a high rigidity of the foundation structures and therefore inability to compensate the deformations of the underground.

A national analysis of approximately 800 cases has indicated the “typical” vulnerable construction: an individual house with a simple ground floor, a non- or inadequately steeled strip foundation, low anchoring depths (< 0.8m) in clayey soils or clayey-sandy soils, and masonry without any horizontal chaining. The susceptible soils are classed sensitive (15<Ip<30) to very sensitive (Ip>30) according to soil humidity variations (with Ip: Plastic index).

Go to 5. What could be the consequences of LANDSLIDES?

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

Go to 5. What could be the consequences of LANDSLIDES?

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).

References:
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

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

Go to 5. What could be the consequences of LANDSLIDES?

The damages caused by a flow event depend on the quantity of material (debris, soil, mud) displaced. In the deposit areas, flows develop successive lobes and can spread on considerable surfaces. These are rapid phenomenon, thus they can be very dangerous for the infrastructures and the population. The socio-economic impact and the loss of life, property and agriculture can be catastrophic in the case of large flows through populated areas. In the case of channelized flows (debris flows), material often overflows the banks and interrupts roadway systems. The deposits are also responsible for severe indirect damages and hazards such as damming of rivers or sudden debris supply to river systems.

Figure 1: Different effects of a flow event on a house (modified from Léone and al., 1996)
Figure 2: Debris flows at Schlans, Switzerland, in 2000 caused the destruction of a part of the village and the death of about 10 people (from Remaître, 2006)
Figure 3: Mudflow at Gondo, Switzerland, in 2000. About 10 people were killed (from Remaître, 2006)
Figure 4: The village of Täsch, Switzerland, damaged by a debris flow in June 2001 (from Ancey, 2007)
Figure 5: Houses damaged by a debris flow at San Matéo, California (from Cannon et Ellen, 1985)
Figure 6: House damaged by a debris flow (from USG)
Figure 7: Road cut off by a debris flow at Hashi, Japan, in 2004 (from Remaître, 2006)
Figure 8: Bridge destroyed by a debris flow occurred in the Pisse torrent, in Reallon, Hautes-Alpes, France, on June 18 2005 (photo by Arnaud)
Figure 9: Bridge and road damaged by a debris flow occurred in the Faucon torrent, in the Barcelonnette Basin, France, on August 19 1996. Debris overflowed 50 cm above the bridge. At the confluence with the Ubaye river, 2 to 4 m-thick debris spread up to a width of 250 m (from Sivan, 2000)
Figure 10: House damaged by a debris flow also occurred in the Faucon torrent, in the Barcelonnette Basin, France, on August 5 2003. The road and the bridge were cut off again, and six houses were damaged (photo by Peyron)
Figure 11: Inhabitants of Angra dos Reis, Brazil, during a mudflow in 2002 (from Remaître, 2006)
Figure 12: Effects of a debris flows in Shields Canyon, California, February 1978 (from Slosson and al., 1992)

References:

ANCEY C., 2007. Notes de cours – Risques hydrologiques et aménagement du territoire. Laboratoire hydraulique environnementale, École Polytechnique Fédérale de Lausanne
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
REMAITRE A., 2006. Morphologie et dynamique des laves torrentielles : Applications aux torrents des Terres Noires du bassin de Barcelonnette (Alpes du Sud). PhD Thesis: Laboratoire Geophen, Université de Caen/Basse-Normandie, 487 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

Go to 5. What could be the consequences of LANDSLIDES?