landslide

Computer simulation : landslide in San Mateo County near San Francisco, 1997

A landslide is the sliding of larger masses of earth and rock, mostly triggered by heavy rainfall (prolonged rain or heavy rain ) and the resulting penetration of water between previously bound layers of soil. Due to the force of gravity and the reduction in static friction between the soil layers, the slope slips (if the slope is sufficiently steep ). A large landslide is also landslide called; if small areas are affected, also landslides or landslides .

A landslide differs from a landslide in that it is slower.

causes

Landslide on the Karakoram Highway , western China

Landslide in Doren in Vorarlberg, Austria

The most common cause is that the soil on the slope has absorbed too large amounts of water, for example as a result of heavy thunderstorms or snowmelt. Due to insufficient internal static friction , this results in a loss of stability along a sliding joint that is being formed .

Other possible causes are:

earthquake
generally tectonic movements
Erosion from wind and frost
Heavy deforestation of the existing forest (death and rotting of the roots stabilizing the soil)
Thawing of the permafrost soil in high mountains or of methane hydrate ( Storegga effect ) on continental slopes due to global warming
Damage to the soil from extensive mining

The risk of a landslide depends on:

the water permeability and water absorption capacity of the soil layers,
the slope of the terrain,
the presence or absence of protective vegetation , the roots of which hold the soil together,

the presence of slippery interfaces, for example along layers of clay .

Shapes of the landslide

A landslide usually moves downwards in a complex, rotating motion. Depending on where they originate, trees, masses of ice or snow or components of human structures can also contribute to the flow of material.

Special forms of landslide are:

The earth slip or the landslide in which earth material slides off as a block along a weak zone

The sagging or rotational slide in which a body of soil slides in a circular path around an axis orthogonal to the slope

The earth flow spontaneously slipping off in as a result of heavy rainfall water saturated soil material and in the form of a debris flow travels relatively great distances

The debris flow , in which water and debris are suddenly and canalized (e.g. in a stream bed) released (debris flow)

Examples of landslides

Type	date	place	Cause / trigger	Damage
landslide	1920	Gansu , China	earthquake	The Gansu earthquake left more than 200,000 dead
landslide	April 22, 1980	Thanheimer Steige am Albtrauf between Bisingen and Albstadt - Onstmettingen , Baden-Württemberg, Germany		When the snowmelt and heavy rainfall came together, a heavy landslide destroyed the entire course of the road over an area of around 16 hectares. The Albaufstieg had to be blocked for three years and completely renewed.
Rock slide	April 12, 1983	at the "Hirschkopf" on the Albtrauf near Mössingen , Baden-Württemberg, Germany		On an area of around 50 hectares, five to six million cubic meters of rock broke off and slid into the depths along with the forest and forest path, a process that has for millennia the eaves of the Swabian Alb, which once reached near Stuttgart , on and on lets back away.
Landslide	Evening of December 11, 2004	Steinbergen quarry , Steinbergen , Lower Saxony, Germany	A wedge-shaped block about 300 m long and up to 50 m wide slid from the ridge of the Messingberg ( Weser Mountains / Lower Saxony) to the north.	Rock masses in the order of magnitude of around one million tons fell like an avalanche up to 300 m into the quarry in front. Deep cracks and crevices have also formed on the south side of the mountain. Other cliff formations (monk and nun) that form the ridge are also at risk of slipping. Negative effects on valuable forest and natural areas of this recreational area used for tourism in the Weserbergland are to be expected.
landslide	Tomorrow, July 18, 2009 around 4:40 a.m.	Concordia Lake in the Harz foreland in Saxony-Anhalt		A strip of land about 350 by 150 meters wide slid into the lake that was created during the large landslide on Lake Concordia .
landslide	November 22, 2015	Kachin State , Myanmar	Overexploitation - static defects in an overburden dump	114 people were killed in a landslide in the spoil pile of a jade mine in northern Myanmar. A mound about 300 meters high slid and buried almost 50 houses. The majority of the dead were villagers who searched the huge heap of the jade mine.
landslide	20th December 2015	Shenzhen , New Guangming Industrial Park , China	Persistent rains	A mudslide broke out of an artificial mountain of rubbish about 100 meters high and covered an area of over 380,000 square meters; over 85 people have been missing since then.
landslide	December 25, 2015	Kachin State , Myanmar	Overexploitation - Static defects in an overburden dump	After the severe landslide of the overburden mound of a jade mine on November 22, 2015, at least 50 people were killed in another landslide.
landslide	May 16, 2015	Salgar , Colombia	Persistent rains	After a landslide with a mudslide and flood, 58 people died and another 37 people were injured. In a similar landslide in 1966, over 100 people died in Salgar.
landslide	June 24, 2017	Diexi , Sichuan , China	Persistent rains	After a landslide with a mudslide and flood, the 62 houses in the village of Xinmo were buried. 15 bodies were recovered and 118 people are still missing.

Shores of Lake Maggiore formed by landslides

Possible countermeasures

Landslides can hardly be prevented, but their effects can be mitigated if the masses of earth are not too large or if you move slowly. The most important point is to remove the water from the slope. There are different measures, including:

Installation of drainage , either on the surface or deep into the subsoil (e.g. drainage anchors);
preventive installations in the endangered subsoil - analogous to torrent and avalanche barriers ;
short-term stabilization of moving slopes through concrete and steel reinforcement (e.g. armored hedgehogs );
with small dimensions also stabilization with sandbags ;
Large areas of critical slope areas are covered with tarpaulin to prevent further ingress of rainwater .
A protective forest often offers effective protection. The roots of the trees consolidate the soil and regulate the water balance (see also root penetration ).
Lawn seeds also stabilize the slope with their fine and strongly branched roots.
Flatten the slope.

However, these measures are powerless against landslides that loosen millions of cubic meters of earth. The best measure against these landslides is prevention.

Bans prevent people from settling in vulnerable areas.
Attention can ensure a warning time before the actual landslide and enable timely evacuation.

Tsunamis due to landslides

A landslide is a common, but usually local, natural disaster . It acts as a disruption to the affected ecosystem and opens up raw soil for repopulation and a restart of the succession .

Landslides in the sea or in lakes, on the other hand, can trigger tsunamis and thus cause destruction even at greater distances. Depending on the size of the landslide, the tidal wave can reach heights of several hundred meters on neighboring coastal slopes ( megatsunami ).

In front of the islands of Hawaii there are large rubble fans that were created by the volcanic flank eruptions. According to estimates by scientists, there are flank breaks with dangerous tsunamis about every 100,000 years.

Landslides with tsunamis are in the list of tsunamis , others are in the list of avalanches and landslides, landslides .

literature

Kyoji Sassa, Badaoui Rouhban, Sálvano Briceño (Eds.): Landslides: global risk preparedness. Springer, Berlin / Heidelberg 2013, ISBN 978-3-642-22086-9 .