A landslide is a large-volume, fast-moving rock and rubble movement from steep mountain slopes . Rock walls that appear stable can also be affected if they are criss-crossed by fissures . In landslides, the rock behaves “like water” over a large area, can reach a speed of over 100 km / h on an inclined slide and even “burn up” on opposite slopes, as can be seen several times in the Upper Inn Valley, for example . The investigation of landslides and their causes is an interdisciplinary topic between several disciplines, v. a. Geology , rock mechanics , engineering surveying and geomorphology , while related warning systems are being developed in recent collaborations between geotechnics and geodesy .
The deposition areas can reach volumes of millions of cubic meters and surface areas of more than 10 hectares. A comprehensive definition of landslides comes from the geographer Gerhard Abele (1974): Rockslides are "rock and debris movements that come down from mountain flanks at high speed in seconds or minutes and have a volume of over a million cubic meters in the deposition area and an area of over Cover 10 hectares. Smaller events are called rock falls ”.
Frank Ahnert defines it in the textbook Geomorphology (1996) instead on the subjective level: “The slope area covered by the movement and the rock mass (or volume) moved must be large enough to be called" landslide "in the opinion of the surrounding population and to do justice to the geomorphologists investigating the event ”.
Rockslides are large-scale rockfalls with sometimes devastating effects. In the remaining rubble can also smaller reservoirs form, sometimes more Abdämmungsseen . A special type of rock fall is the ice fall with a far excessive damage surface, as the ice (together with debris) is transported further, the ice, also called fall ice, melts or even evaporates due to the frictional heat and thus an effect similar to that of a hovercraft can arise .
Rockslides usually occur at the boundary between two or more rock layers and at tectonic fault lines , when such interfaces are weakened by earthquakes , extreme weather events (heavy rainfall or temperature fluctuations) or when a glacier melts and its counterpressure is missing. Increasing rockfall activity can be an indication of imminent landslide events. Human interventions in nature (clearing of slopes, forest roads that are too wide , mining of raw materials) can accelerate these processes, as was the case with the Elm landslide in 1881. Alongside mudslides and avalanches, rockslides and landslides represent the main danger of natural phenomena in the mountains .
A distinction is made between the more common slip falls and the rarer fall falls. A slip-fall begins with a sliding movement in which the sliding mass remains largely in the bond or completely disintegrates into small parts. Trapped air, which acts like an air cushion between the solid subsurface and the slipping, disintegrating rock mass, can cause slip falls even in rock sections without a large amount of water. In the case of a fall, on the other hand, there is practically an immediate demolition in which the rock is in free fall.
The rise in temperature associated with climate change and the associated thawing of the previously stabilizing permafrost increases the risk of landslides. The historical geology knows landslides with these causes from earlier warm periods .
The material left behind in landslides forms a dump , known in Switzerland as the "landslide cone"; Larger boulders are often marked with red numbers for orientation in such block heaps (e.g. for measurements or environmental projects). After long periods of time, landslides can also create attractive landscapes. Typical for the deposition area is a hilly relief (so-called Toma hill ) with mostly clear demarcation from the surroundings.
The speed of a landslide when it hits the ground can - depending on the height of the fall - exceed 100 km / h. On a steeply sloping slide , the speed of the rock avalanche can increase further to 200 km / h, on a glacier even more. It depends on the total mass, the material and its evaporation as well as the sliding friction of the subsurface.
A landslide event causes significant changes in both the demolition area and the deposition area. In the demolition area, for example, there can be secondary falls and sagging movements at the upper edge of the demolition walls. Other consequences of landslides can be:
- Formation of landslide lakes, relocation of water courses and watersheds
- Formation of debris cones
- Development of its own landslide vegetation
- Epigeneses .
Especially in more densely populated areas, cultural buildings and human lives are also endangered, especially by
- Spilling of settlement areas and traffic routes (roads, railway lines)
- direct tidal waves when rock masses fall into larger bodies of water
- unstable damming of rivers and streams, which can later lead to tidal waves, especially when rockslide reservoirs erupt.
Size information on rockslides and rockslides
In order to assess the size and impact of landslides and rockfalls, information is usually given on the volume of the relocated rock mass and the extent of the area where it is deposited. In the case of landslides, volumes in the range from millions to billions of cubic meters and deposits from a dozen to over a thousand hectares. In the case of medium-sized to large rockfalls, the volumes are a few thousand to a few hundred thousand cubic meters with areas of deposit in the hectare area.
For masses that have fallen into the valley floor and may have dammed up a flowing body of water, there is often information about the length and up to what height above the valley floor the valley was laid and up to what height the rock mass on the opposite slope was burned up .
In order to estimate the energy converted in a rock or rock fall (from potential energy to heat , deformation work and chemical energy bound in the deposited rock ), information on the mean fall height is required, which can be estimated from the height and mass distribution in the demolition and deposit area. For the largest known landslide events such as the Flims landslide , careful estimates are made of converted energies beyond 100 petajoules (10 17 joules).
The following tables show the conversion between different units and the related differences in size.
|Magnitude||Conversion into smaller units||Clear correspondence|
|thousand cubic meters (1,000 m³)||Volume of a cube with||10 m edge length|
|1 million cubic meters (1,000,000 m³)||100 m edge length|
|1 cubic kilometer (1 km³)||1 billion cubic meters
or 1000 million cubic meters
|1 km edge length|
|Magnitude||Conversion into smaller units||Clear correspondence|
|1 hectare (1 ha)||10,000 square meters (10,000 m²)||Area of a square with||100 m edge length|
|1 square kilometer (1 km²)||100 hectares (100 ha)
or 1 million square meters (1,000,000 m²)
|1 km edge length|
Prehistoric landslides can be recognized on the basis of the geological nature of the soil and the surface shapes in the area of demolition and in the deposition area.
- Pyhrnpass (Austria): a landslide possibly triggered by the Ries event 300 km away (about 15 million years ago) diverts the northward course of the Ur- Enns to the south, into the Graz Basin .
- Langtang Valley (Nepal): 40,000 years ago, 10 to 15 km³ of rock from a previously up to high mountain in the main Himalayan ridge fell into the valley , probably as a result of an earthquake at the main Himalayan fault . Most of this, apart from a remainder of 2 to 3 km³, has already been cleared by subsequent glacier activity. The still preserved demolition ridge runs over up to high peaks and ridges. In the area of the 24 km² extensive deposit area is the high Tsergo Ri , with whose name the event is often associated, but whose summit is itself part of the landslide mass. It is considered to be the world's largest landslide event in crystalline rock .
- Flims rockslide (Switzerland, Graubünden): Approx. 12 to 15 km³, about 10,000 years ago.
- Fernpass (North Tyrol): Caused by a landslide on the western slope about 4000 years ago.
- Storegga (Central Norway): Under water and with a tsunami as a result. Around 8,000 years ago, the mass of the fall must have been more than a hundred times greater than in Flims. It also had an impact in Scotland and Iceland.
- Dobratsch (Carinthia): Approx. 0.9 km³ rock masses fell into the Gailtal .
- Davos (Switzerland, Graubünden): Well over 0.3 km³ fell from the Totalp in the Parsenn area , forming the Wolfgang Pass and Lake Davos. Dating: younger than 8000 years.
- Köfels (Tyrol): About 8,700 years ago over three cubic kilometers of rock fell from the western slope into the middle Ötztal near Umhausen and blocked the Ötztaler Ache , which later had to eat its way through a ravine (Maurach) through the rubble. The frictional heat caused the rockslide to transform gneiss into a glassy rock known as Köfelsite .
- Tschirgant (Tyrol): 240 million cubic meters of rock mass plunged into the Inn valley and the front Ötztal around 4,000 years ago, leaving behind a deposit area of 13 square kilometers.
- Wildalpen ( Styria ): About 4000 BC fell from the Ebenstein and Brandstein ( Hochschwab group ). Huge rock masses to the north and broke as a torrent into the Salzatal.
- Almtal ( Upper Austria ): A large mass of rock fell from the northern roof of the Dead Mountains into the Hetzau, where possibly the remainder of an Ice Age glacier or a lake or swamp lay. As a result of the frictional heat , the rock slid on a carpet of water or even steam far out into the Almtal, where it only came to a standstill in Heckenau immediately south of Grünau in the Almtal . The Tomahügel of the Ödseen to Cumberland Park due to this rush current.
- Hocharn im Raurisertal ( Salzburg ): The eastern flank of the Hocharn (Grieswies-Schwarzkogel) plunged into the head of the Kolm-Saigurn valley and surged up again on the eastern flank towards the Filzenalm. The irregular hill of the through forest ( Rauris primeval forest ) interspersed with varnish represents the fall mass.
- Hochkaltermassiv : A landslide of around 15 million cubic meters from the Blaueistal around 3500 to 4000 years ago dammed the Ramsauer Ache to the Hintersee and created the magic forest . It covers an area of 0.75 km², which is located between the Hintersee and the Marxenklamm.
- Marocche di Dro (Italy): The result of several landslides in the lower Sarca Valley, the first of which occurred between 2950 and 2600 BC at the earliest. And the last of these (the frana di Kas ) dates from 400 to 200 BC at the earliest. Occurred. The total volume of the landslides was around 1 km³.
- Vom Schafberg : estimated 50-100 million m³, separated Attersee and Mondsee and could be around 3200 BC. BC by the inland Tentsunami the pile dwelling settlements of the Mondsee culture wiped out.
- 1172: A major landslide falls on the moraine wall between Königssee and Obersee in the Berchtesgaden Alps .
- November 24, 1248: Mont Granier in the Chartreuse massif near Chambéry in the Savoy : landslide on the night of November 25 of around 150 million m³ of rock with a scree length of seven kilometers, Saint-André with around 3000 people totally buried, 16 villages were also buried, an estimated total of up to 5000 dead.
- 1348 - Dobratsch (2100 m) near Villach in Carinthia: triggered by the Friuli earthquake , an estimated 150 million m³ of rock masses fell into the Gail Valley in the same area in which a prehistoric landslide took place . The demolition area on the south-eastern rock face is still clearly visible as the red wall . Its deposit area extends 3 km to the Gail , bears the name Die Schütt and is under nature protection. The new village of Oberschütt was founded between the Schütter forest and the river (in January 2015, almost 2,000 m³ of rock fell from the Rote Wand onto the forest below. The demolition point and the new debris cone can be clearly seen from the viewing platform at the Alpine Garden ).
- September 30, 1512: Buzza di Biasca landslide in the Blenio Valley north of Biasca . The rock dammed up a lake; the dam broke in 1515 and devastated the Ticino valley as far as Lake Maggiore .
- April 3, 1595: landslide in Reurieth from the so-called "Reuriether Felsen". Before that, a landslide is said to have buried the village as early as 1137.
- August 24, 1598: landslide from Wartha above the Glatzer Neisse in Bardo Śląskie , Poland.
- September 4, 1618 (Julian calendar: August 25) Rockslide from Plurs (near Chiavenna on the road to the Malojapass, then Drei Bünde, now Italy): Here an entire city including the district of Scilano (Schilan) died, according to contemporary sources between 930 and 1200 people. The before-and-after documentation by Matthäus Merian is also significant in the history of research .
- July 16, 1669 - Rock fall of 1669 in the city of Salzburg / Austria: Two rock falls from Mönchsberg , which consists of loose Nagelfluh , cost 230 people their lives in Gstättengasse. Since then, mountain cleaners have been working here .
- 1714 and 1749: Two landslides on the Les Diablerets , one of them created the Lac de Derborence reservoir .
- September 2nd, 1806 Rockslide in Goldau / Switzerland: Here an entire village of 40 million m³ of rock was buried, 457 people died.
- March 10, 1876 Kaub am Rhein landslide : eight houses were buried, 25 people died.
- September 11, 1881 Elm / Switzerland: ten million cubic meters: The Elm landslide was caused by years of ruthless mining of slate . 115 people died.
- April 29, 1903 Rockslide in Frank ( Frank Slide ), Alberta (Canada): 30 million m³, one of the most famous rockslides: a cliff broke off over a very steep flank with an altitude difference of around 1000 meters.
- February 18, 1911 Saressee / Pamir , Tajikistan : an earthquake caused a landslide of 2.2 km³, which formed the highest dam in the world and the 55.8 km long Saressee.
- April 10, 1939: The Fidaz landslide occurred east of the village of Fidaz in the municipality of Flims in the Swiss canton of Graubünden . 100,000 cubic meters of rock fell into the valley. 18 people were killed.
- July 10, 1949: A by an earthquake-triggered landslide in the Pamir met above the Tajik village Chait altitude lake Chaus-Chait . The resulting mudslide rolled over the place and buried around 18,000 residents under a twenty to thirty meter high layer of mud and rubble.
- July 9, 1958: A landslide that ran into the Lituya Bay , Alaska , with an estimated 90 million tons of rock and ice , causing a tsunami that spilled over at least a 520 m high hill.
- October 9, 1963: Vajont (Longarone) disaster , 90 km north of Venice in Friuli / Italy: rockslide of 260 million m³ in a reservoir, around 2000 people lost their lives.
- January 9, 1965: landslide of Hope (Hope Slide) in Hope , British Columbia, Canada: 46 million cubic meters of rock and rubble poured into a stockpile of 70 m in height and 3 km in length to the valley. A lake was completely filled in and four people died.
- August 30, 1965 - Mattmark , Saas-Almagell, Wallis / Switzerland: Ice fall 500,000 m³, 88 dead.
- since 1993 - Bischofsmütze in the province of Salzburg: on September 22nd, 1993 a pillar more than 200 m high fell from the rock face into the abyss. Since then, there have been repeated small rock falls.
- May 31, 1970: Yungay , Peru : As a result of an earthquake with a magnitude of 7.8, around 60 million cubic meters of ice and rock fell from the Nevado Huascarán, killing over 70,000 people in the Callejón de Huaylas valley , injuring around 150,000 and leaving well over 500,000 homeless . The city of Yungay with around 5000 inhabitants was completely destroyed, only around 400 survived. Today around 10,000 people live next to the memorial again.
- Mar. 18, 1971 - Chungar : 100,000 m³ of rock loosened from the limestone 400 m above the lake Lago Yanahuin and caused a tidal wave up to 30 m high, which buried the opposite bank, destroyed almost the entire mining settlement and (according to different estimates ) Killed 400–600 people.
- July 28, 1987 - Morignone in Val Pola in the province of Sondrio / Italy ( Valtellina ): 40 million m³
- April and May 1991 - Randa / Switzerland: 30 million m³.
- September 23, 1995 - Breitachklamm in the Allgäu : At 6:00 am, around 50,000 m³ of rock and rubble loosened, causing 300,000 m³ of water to be dammed up to a height of 30 m. On March 23, 1996, at 11:30 a.m., the breakthrough took place, completely devastating the gorge.
- July 10, 1999 - Schwaz in Tyrol: In the Eiblschrofen mining area , around 150,000 m³ of rock fell into the mountain forest below and threatened a district. 250 residents had to be evacuated and were only able to return to their homes after several weeks and extensive security measures.
Rock falls from 2000
- October 14, 2000 - Gondo on the Simplon Pass , Valais / Switzerland; Border town to Italy: mountain debris flow with tremendous speed and a volume of several 10,000 m³, eleven dead and two missing (no actual rock fall).
- May 31, 2006 - Gurtnellen : Rock fall on Autobahn 2 (Switzerland) with two dead motorists.
- July 13, 2006 - Eiger : 500,000 m³ of rock fell on the Lower Grindelwald Glacier .
- October 30, 2006 - Dents du Midi : Approx. 1 million m³ of rock fell from the Dents du Midi mountain in Val d'Illiez (Wallis / Switzerland) into the valley. There was no personal injury or property damage. The unusually warm summer was suspected to be the reason for the rock fall.
- October 12, 2007 - Sexten : Approx. 60,000 m³ of rock and rubble fell from the Einserkofel above the Fischlein valley near Sexten-Moos into the valley. Dust enveloped the valley, there were no injuries.
- December 2011 and August 23, 2017: Rockslides from Bondo with around 1 and 4 million m³ of rock volume. The latter landslide caused extensive damage to the village via a mudslide.
- December 24, 2017 - Vals (Tyrol) : 117,000 m³ of rock spilled the state road, 3 houses were evacuated, an emergency route was built.
- October 12, 2019 - Trossingen : Rock slide at night on the Autobahn 81 . A car drives into the boulder at high speed and catches fire. The driver is killed.
Melting stone in major landslides
In 1895, the Ötztal pastor Adolf Trientl , who was also a natural scientist , became aware that carpenters were using local pumice stone for wood grinding , the origin of which the Innsbruck geology professor Adolf Pichler asked, traced back to the activity of a local volcano . However, this theory could not be substantiated any more than the idea of a large meteorite impact . The mineralogist and petrologist Ekkehard Preuss from Regensburg, who was particularly interested in meteorite impacts , began researching the pumice stone sites and the surface shape of the landslide from 1962 and came to the conclusion that the sequence required for the theory - first meteorite impact, then landslide - could not be correct.
The phenomenon of the pumice stone deposits was then clarified by Theodor H. Erismann , the then director of the Eidgenössische Materialprüfungs- und Versuchsanstalt in Dübendorf near Zurich. When about 8000 years ago 3 km 3 of rock slid from the Köfels into the Ötztal, the sliding masses reached speeds of 150 to 200 km / h. The friction in the area of the sliding surface led to such a great heat development under the high weight pressure that the gneiss began to melt after a distance of 100 m. At Köfels the temperatures exceeded 1700 ° C. While the gneiss melted, the calcite contained in small quantities was broken down into quicklime and carbon dioxide by the heat. The resulting gas cushion and the rock melt formed an excellent lubricant for the whole mass. The "pumice stone" from the Ötztal is now called Köfelsite after its place of discovery in Köfels .
The aforementioned Preuss found a similar scenario in 1973 after information from earlier Himalayan expeditions in the Nepalese Langtang Valley , about 60 km north of the capital Kathmandu and located on the main Himalayan ridge, where about 40,000 years ago in the area of today's Tsergo Ri 10– 15 km 3 of rock had slipped. According to a calculation by the scientists, such a large mass movement released enough energy to shoot a mass the size of the Cheops pyramid into orbit. It is believed that the massif around Yala Peak and Tsergo Ri are the remains of an 8000-meter peak that collapsed in the landslide . A strong earthquake at the main central thrust of the Himalayas is assumed to be the likely trigger .
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- Albert Heim : Bergsturz und Menschenleben (= supplement to the quarterly the Natural Research Society in Zurich. 77, supplement No. 20, ). Come. Beer & Co, Zurich 1932.
- Melchior Neumayr : About landslides. In: Journal of the German and Austrian Alpine Club. Vol. 20, 1889, , pp. 19-56.
- Welsch, Walter (1984) Rockslides caused by earthquakes. Geosciences in our time; 2, 6; 201-207; doi : 10.2312 / geosciences . 1984.2.201 .
- The website for the Goldau landslide of 1806
- Rockslides in the Alps
- Rockslides in Austria
- Big rock fall in Sexten 2007
- Rockslides in the Alps and global events
- Rockslide in Bergell. Website of the German Alpine Club eV on the event of Bondo 2017
- Gerhard Abele: Rockslides in the Alps, their distribution, morphology and sequelae (= Wissenschaftliche Alpenvereinshefte. Vol. 25, ). Deutscher Alpenverein, Munich 1974, p. 21, (At the same time: Karlsruhe, University, habilitation paper, 1972).
- Frank Ahnert, Geomorphologie 1996, quoted in in Wissen.de/Bergsturz
- Zinal Glacier ( memento from October 29, 2013 in the Internet Archive ) globezoom.info
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- National Park Flyer , published by the Berchtesgaden National Park Administration, as of July 2015
- Dieter Groh , Michael Kempe, Franz Mauelshagen (ed.): Natural catastrophes. Contributions to their interpretation, perception and representation in text and images from antiquity to the 20th century (= literature and anthropology. Vol. 13). Narr, Tübingen 2003, ISBN 3-8233-5712-3 .
- Tour report "Between Pamir and Desert"
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- Yungay Erdsturz ( Memento of 11 April 2008 at the Internet Archive )
- Helmuth Ackermann: Solid Band - Ekkehard Preuss . In: Acta Albertina Ratisbonensia . tape 47 , 1991, pp. 7–16 ( full text [PDF; 1,2 MB ]).