4.1. More information on Where do landslides occur

As these phenomena are usually to be found in mountain or coastal regions owing to the instability of slopes and cliffs as well as on plains and plateaux when associated with the use or dissolution of the sub-soil, they can happen all over the world. Slides can occur in various areas. In hilly and mountainous regions, many shallow slides occur in depressions or small valleys, where slopes converge because it corresponds to preferential location of water. Mountainous marly and clayey slopes are often affected by shallow or deep slides. In these materials, slides are classically associated with gullies. An example is the Barcelonnette Basin, in the French Southern Alps, affected by both slides and gullying processes since several centuries. Rotational slides generally occur in homogeneous loosed formations (substratum or superficial deposits). Slides are also often associated with flows in materials such as marl, flysch, clay, schist. Near St-Jean-de-Maurienne, in France, flows and slides mainly occur on schistose slopes. Many coastal slides exist in Normandy, France. Sub-marine slides also occur. Falls, by definition, occur on steep slopes or cliffs. Moreover, climatic factors play a direct part in the triggering of falls, in particular the alternate freezing and thawing of infiltrated water, which is particularly active in high mountainous areas or at high latitudes. Falls affect sedimentary (limestone, sandstone), eruptive (basalt, dolerite) or metamorphic (schist) rocks. In the latter the exfoliation into small columns may provoke slow tilting which gives rise to colluvial deposits. As for falls, topples occur on steep slopes or cliffs. Topples in rocks usually require high cliffs, whereas topples in debris and soil fail on lower cliffs. Topples are frequent in coherent, tectonised and fractured rocks. Topples affect sedimentary (limestone, sandstone), eruptive (basalt, dolerite) or metamorphic (schist) rocks. In the latter the exfoliation into small columns may provoke slow tilting which gives rise to colluvial deposits. Loose earth types prone to topples include more or less compacted sand and clayey soils in which desiccation and humidification cracks may appear. Flows occur in highly fractured rocks, clastic debris in a fine matrix or a simple, usually fine, grain size. Debris flows and debris avalanches usually start in the upper parts of slopes from slides (debris slide, slab slide) in loose unconsolidated rocks and soil debris, especially where the vegetative cover has been removed by logging or fire. They are also frequent in topographic concavities or hollows at first-order watersheds. This geometry favours the accumulation of colluvium and the convergence of groundwater flow necessary to cause the failure. Soil flows occur in wet sands or in silty-clays which are so reworked with water or so liquefied by structural collapse that they adopt a flow mode. Soil flows may also occur in dry sand (dry sand flow); these are potentially very destructive but very rare. They originate when large masses of dry non-cohesive fine-grained material fall from steep slopes and fluidise on impact. Rock flows are produced only where slopes are high enough to induce strong gravitational stress in the bedrock. Such condition is typical of valley slopes in strongly uplifted areas, mountain fronts, high coastal cliffs and recently deglaciated mountain areas. There are a lot of large landslides all over the world. To have an idea is possible to see the short list below on the worldwide catastrophic landslides of the 20th century :
Year Place Event Cause Deaths
1933 Sichuan, Deixi landslide EQ* M=7.5 6800
1949 Tadzhik, Kahit rock slide EQ* M=7.5 ca 15000
1958 Japan, Kanogawa debris flow Typhoon 1094
1962 Peru Huascaran debris aval. ? ca 5000
1962 Peru Huascaran debris aval. ? ca 5000
1963 Italy , Vaiont rock slide Reservoir fillin 1909
1964 Alaska slides EQ* M= 9.4
1970 Peru, Huascaran debris aval. EQ* M=7.7 18000
1980 Washington debris aval. Volcanic
*Earthquake Many of the catastrophic landslides occurred as an effect induced by earthquakes and volcanic eruptions. For more details go to 4.1.1. Catastrophic landslides of the 20th century worldwide or to http://landslides.usgs.gov/learning/majorls.php One of the most worldwide catastrophic landslides has been the debris avalanche from Nevado Huascaran, in the northern coast of Peru’. In 1970, an earthquake-induced a debris avalanche on Mt. Huascaran which buried the towns of Yungay and Ranrahirca. The death toll from the Debris Avalanche was 18,000 (total fatalities from the earthquake and the debris flow was 66,000). The avalanche started as a sliding mass of glacial ice and rock about 3,000 feet wide and one mile long. The avalanche swept about 11 miles to the village of Yungay at an average speed of about 280 km/h. The fast-moving mass picked up glacial deposits and by the time it reached Yungay, it is estimated to have consisted of about 80 million cubic yards of water, mud, and rocks. The same phenomenon occurred in the same place on 1962 and caused ca 5000 deaths. For more details on 1962 and 1970 phenomena go to http://news.bbc.co.uk/onthisday/hi/dates/stories/january/11/newsid_3306000/3306665.stm http://landslides.usgs.gov/learning/photos/international/peru_earthquake_mt._huascaran_1970/nevadohuascaran.gif
Image of the 1970 debris avalanche from Mt. Huascaran (Peru') (Photo courtesy of Servicio Aerofotografico Nacional de Peru, 13 June 1970; from http://news.bbc.co.uk/onthisday/hi/dates/stories/january/11/newsid_3306000/3306665.stm)

Anyhow, the world’s biggest historic landslide, in terms of volume of material involved, occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington. USA. It has been a rock slide – debris avalanche and the volume of material was 2.8 km³. The phenomenon began as rock slide deteriorated into 23-km-long debris avalanche with average velocity of 125 km/hr.;surface remobilized into 95-km-long debris flow The evacuation saved lives; in fact, the rock slide – debris avalanche took low deaths (only between 10 and 57 human fatalities, according to different information sources) but major destruction of homes, highways, etc.occurred

The Mount St. Helen rock slide - debris avalanche (Photo by http://www.fs.fed.us/gpnf/global/images/20070727-1401-hd-lg.jpg)

For more information go to
http://pubs.usgs.gov/fs/2000/fs036-00/
http://news.bbc.co.uk/onthisday/hi/dates/stories/may/19/newsid_2511000/2511133.stm

As concerns Europe, the largest catastrophic landslide was the rock slide (volume of 270 million m3) which on 9 october 1963, with high-velocity, fall into Vaiont Reservoir (see photo in the Landslides introductory page). It caused 100-m-high waves that overtop the Vaiont Dam, channellized into the narrow Vajont gorge, plunging like a drop hammer onto Longarone and other villages along the Piave River valley.
This phenomenon caused 1909 victims.
For more information go to 13.1 Vajont study case

Location of the main region prone to landslides in West Europe
In blue: plateaux and plains with subsidence;
In yellow: high mountains and hilly areas

As concern the subsidence (progressive and rapid subsidence processes) in Western Europe, accordingly to the geologic conditions which advantage this phenomenon, it is mainly located in areas:

  • Where natural cavities exist, i.e. in soluble bedrocks like limestone, chalk, gypsum, salt, etc. In karst areas the creation of tunnels and cavities can be very rapid when aggressive water (i.e. water with a high content of carbonic acid) dissolves soluble rocks like gypsum or salt, . In such locations the development of large cavities can occur in a few years, whereas dissolution is much slower in limestones or chalks where the development of cavities can take far more than a hundred years;
  • Where anthropogenic cavities exist (subterranean quarries or mines), i.e. in the main coal, saline and iron basins (mining), and in many urban zones (quarries) (Link with study case Caen-Carries) because a lot of cities were built with stones or materials extracted in direct vicinity, and urbanization often forced the settlement into the zones of exploitation. Go to 4.1.2. Where subsidence occur in Western Europe

Shrinking is a process caused by the desiccation of the soils due to intense and/or long periods of dryness. Shrinking produces slow, low amplitude, vertical deformations of the ground surface. Shrinking can be followed by progressive swelling processes when soil humidity is increased in the wet seasons In many regions, these vertical movements have generated high damage to buildings, in particular to small single, individual houses. Go to 4.1.3. Where shrinking-swelling occur in France

References:

– DIKAU R., BRUNSDEN D., SCHROTT L. & IBSEN M.-L. (eds.), 1996. Landslide Recognition: Identification, Movement and Causes. John Wiley & Sons Ltd, Chichester FLAGEOLLET J.C., 1988. Les mouvements de terrain et leur prévention, Masson, Paris, 224 p. 

Main locations of subsidence (paragraph common to progressive and rapid subsidence processes)

Accordingly to the geologic conditions which advantage subsidence, it is mainly located in areas:

  • Where natural cavities exist, i.e. in soluble bedrocks like limestone, chalk, gypsum, salt, etc. In karst areas the creation of tunnels and cavities can be very rapid when aggressive water (i.e. water with a high content of carbonic acid) dissolves soluble rocks like gypsum or salt, . In such locations the development of large cavities can occur in a few years, whereas dissolution is much slower in limestones or chalks where the development of cavities can take far more than a hundred years;
  • Where anthropogenic cavities exist (subterranean quarries or mines), i.e. in the main coal, saline and iron basins (mining), and in many urban zones (quarries) (Link with study case Caen-Carries) because a lot of cities were built with stones or materials extracted in direct vicinity, and urbanization often forced the settlement into the zones of exploitation.

According to Embleton and Embleton (1997) to Maquaire (2005), for some countries in Western Europe the zones prone to subsidence processes are: In Luxembourg in the Walfendigen sector: Some collapses caused by natural dissolution and the mining of gypsum. In The Netherlands near Maastricht and St Pietersberg: Subsidence caused by coal mining from 1900 to the mid 1970s, and by the marl excavation since the seventeenth century. Furthermore, subsidence is still occurring in regions where oil and gas are extracted at or close to the coastline, in particularly near the Groningue basin. Further causes for subsidence in coastal areas of the Netherlands are the compaction of Holocene sediments and a decrease of the water table pressure in recent polders. These polders have been artificially filled with a one meter layer of sand to improve the state of the built-up land (Flageollet, 1988). In Germany in the region of the Hartz Mountains and along the fringes of other central German uplands (Mittelgebirge) in Hesse, Lower Saxony and Thuringia, and also at a few localities in the north German lowlands: Soluble formations in subterranean caves have collapsed (sulphate and chloritic rocks, to a lesser extent calcareous rocks) due to karst processes. Natural karst processes, which seem to have been more active in the early Tertiary and late Pleistocene, actually show only weak effects, but mining engineering, copper and salt mining, and water pumping have intensified and modified these natural processes, sometimes leading to local damage (Garleff et al., 1997). At Lüneburg (Lower Saxony), 169 buildings were demolished between 1949 and 1973 because of subsidence caused by salt mining and the karstification of gypsum (Flageollet, 1988).

In Belgium, there are mass movements and subsidence associated with karst processes in the limestone fringe along the north of the Ardennes, in the Condroz region and also near Doornik and the region of “Pays de Herve” (Heyse, 1997). Furthermore, collapses and subsidence due to marl excavation occur regularly since the seventeenth century in the Muizenberg, associated with the marl excavation in various part of Belgium (areas of Zichen-Zussen-Bolder, Riemst, Kanne and Hoegaarden). Coal mining causes subsidence and considerable damage to buildings, roads and infrastructure in the Campine region as well as in Wallonia, in the Borinage, and in the Liège Basin.

In France, subsidence caused by human activity has been observed in the coal basins, the Lorraine iron and salt mine, above underground quarries (marl, gypsum, chalk…) in the Paris region, the North Pas-de-Calais basin, the Val-de-Loire, the Bordelais and the Touraine, the city of Caen (link Study case) ; the Pays d’Auge and the plateaux in the Seine-Maritime and the Eure. The dissolution of karst also entails subsidence, in the Paris region in the gypsum, in the Orleans region in the chalk, in the Causses du Quercy, in Perigord, etc.

Bibliography:

Embleton, C., and Embleton C. (eds.) (1997), Geomorphological Hazards of Europe. Developments in Earth Surface Processes 5. Amsterdam : Elsevier, 524p.
Flageollet, J. C. (1988), Les mouvements de terrain et leur prévention, Paris : Masson, 224p.
Maquaire, O., (2005). Geomorphic hazards and natural risks, In: Koster, E., A. (ed.), The Physical Geography of Western Europe, Oxford Regional Environments, Oxford University Press, Chapter 18, 354-377.
Ministère de l’Ecologie et du Développement Durable, 2004. Dossier d’information sur le risque Mouvement de terrains, 20 p. (à télécharger sur site du MEDD).

Liens Internet :

http://fr.wikipedia.org/wiki/Subsidence
http://www.lorraine.drire.gouv.fr/mines/g_cadreDomaine.asp?droite=2_ApresMines.asp&bas=g_MinesNavig.asp?DEST=APMINES
http://www.cgm.org/themes/soussol/mines/
http://www.cavite.net
http://www.prim.net/professionnel/documentation/dossiers_info/nat/low/mouvtTerr.pdf
http://www.catp-asso.org/cavites37/pages/missions.htm
http://clamart.cyberkata.org/

Hence, high damage related to shrinking and swelling has been recorded. Since 1989, it is more than 5 000 communes for 75 departments, which were affected par the shrinking-swelling. This phenomenon is largely distributed. However, certain areas are more particularly affected in close relation with the geological nature of the ground. It is the case in particular of the plain of Flandres, the southern part of the Basin of Paris, the graben of Limagne, the area of Apt and especially of the whole of the molassic slopes of South-west, between Agen and Toulouse and many others to a somewhat lesser extent.

In the figure we could see a number of times that a commune was recognized in a ‘state of natural disaster’ (following the law of 13 July 1982) with respect to shrinking-swelling until August 15, 2006 (from http://www.argiles.fr/)

References:
Bekkouche N. et al., 1990. Foundation problems in Champlain clays during droughts: I – rainfall deficits in Montreal (1930-1988). Revue Canadienne de Géotechnique, vol. 27, n°3, pp. 285-293.
Bekkouche N. et al., 1992. Foundation problems in Champlain clays during droughts: II – Cases histories. Revue Canadienne de Géotechnique, vol. 29, n°2, pp. 169-187.
Biddle P.J. 1983. Pattern of soil drying and moisture deficit in the vicinity of trees on city soils. Géotechnique, vol. 33, n°2, pp.107-126.
Driscoll R. 1983. The influence of vegetation on the swelling and shrinking of clay soils in Britain. Géotechnique, vol. 33, n°2, pp.93-105.
Maquaire, O., 2005. Geomorphic hazards and natural risks, In: Koster, E., A. (ed.), The Physical Geography of Western Europe, Oxford Regional Environments, Oxford University Press, Chapter 18, 354-377.
Margron P., Mouroux P. & Pinte J.C. 1988. La construction économique sur sols gonflants. BRGM-REXCOOP. BRGM Ed., Manuels et méthodes, 125 p.
Ministère de l’Environnement, 1993, Sécheresse et construction : guide de prévention. La Documentation Française, 51p.

Internet links :
http://www.prim.net/professionnel/documentation/dossiers_info/nat/low/mouvtTerr.pdf
http://www.argiles.fr/