Flims rockslide
The Flims landslide took place 9480 to 9430 years ago ( calibrated ). With a volume between 9 km³ and 12 km³, it is the largest alpine landslide event (around 300 times larger than the landslide in Goldau and around 1200 times larger than the landslide in Elm ) and one of the largest currently known landslides in the world. (For comparison: The water volume of Lake Lucerne is 11.9 km³) The holiday resort of Flims lies on the transition from the sliding surface in the north to the debris in the south . To the north of Flims, cliffs rise up to 350 meters and in the south lies a densely wooded, unclear hilly landscape with lakes and a wild gorge, the Ruinaulta . The landslide is hidden from travelers by forest; because the debris cone is of no agricultural interest, it remained an extensive forest area. The forest is the namesake for the Vorderrhein Valley: The Romanesque Surselva means "whether the forest".
description
The crack is at about 2700 m above sea level. M. , Flims lies at around 1100 m and the filled in glacial trough valley at around 600 m . The falling mass consisted of Mesozoic limestone , which was 300 to 500 meters thick and slid on a slide from 20 ° to 25 °. The valley floor should have been 1500 meters wide. The rubble piles up to 750 meters above it and covers an area of over 52 km². Most of the lintel mass was completely shattered, although the original structure with the stratification was partially preserved. Countless huge limestone blocks lie on the wooded surface. The Vorderrhein was dammed by the landslide . The result was a large reservoir, the Ilanzersee , which, however, has long since drained through the Ruinaulta. Obviously, however, the Rhine has not yet reached the original valley floor.
A careful estimate of the energy converted in the landslide, assuming a relocated rock volume of 8 km³, a rock density of 2200 kg / m³ and an averaged vertical displacement of the fall mass over 1100 meters in altitude, came to a value of 1.9 · 10 17 joules (190 terajoules ).
Dating
In 1997, wood from the Rabiusa Gorge was first dated using the C-14 method . In 2005 this age was confirmed with the method of cosmogenic radiation and this data was specified in a further study. Lake sediments on the fall have been dated and wood has also been found in the fall mass. The result was a calibrated age of around 9500 years. Work on sediments in the Dachlisee ( 1137 m ) near Obersaxen could not give a clear dating. Contrary to earlier assumptions, no action from glaciers was found on the landslide mass. According to the dating , the nearby Tamins landslide (volume not known) must have occurred at a similar time (± 1000 years) as the Flims landslide. It is believed that it came off before the Flims landslide and blocked the Rhine Valley with a dam.
reasons
In the maximum stage, the Vorderrheingletscher is likely to have been well over 1500 meters thick with a width well over 5 km. Ice is flowing and wants to expand. There is tremendous pressure not only downwards, but also on the mountain flanks. This pressure can plan off the rock together with the debris carried in the ice and shift the layers of layers. This creates shear zones, which loosen and brittle the layers. Water flowed into these shear zones. After the glaciers retreated, the permafrost continued to have an impact and disappeared several centuries later. The delayed triggering of the landslide could be due to the thawing of permafrost, as frost depths of several hundred meters were proven in the Alps during the Ice Age.
Effects
Long-range effects of the Flims landslide reach as far as Lake Constance , where sediment anomalies were found. In the Domleschg to Thusis there are gravel sediments which, according to the current state of knowledge, were mobilized by the Flims landslide and flowed into the Hinterrheintal. The Toma hills in Chur are also causally linked to the Flims fall. As a result of the landslide, several landslide reservoirs were created: the Ilanzersee, the Versamer See, the Lake of Mulin, the Laaxersee , the Lag Segnas and the Lag di Plaun. The largest was the Ilanzersee. The landslide mass falls below the level of 1000 m above sea level only in a few places . M. Presumably the same applies to the area of today's Ruinaulta. Overflows are nowhere to be found. But the level of the Ilanzersee never seems to have exceeded the maximum level of 936 m, at least nothing indicates this.
After the landslide, the Ilanzersee took several years to fill, after which a dam soon broke. However, the lake did not empty completely, but remained at the level of 820 to 840 m for at least 1000 to 2000 years. This is evidenced by lake sediments. The Ilanzersee probably had an original volume of more than 3 km³, the remaining lake at 820 m height still 1.5 km³. The falling mass is heavily compressed in many areas, which results in high stability, but the sliding mass is still not solid rock.
The debris is mined at Versam in a gravel works.
Visit, information and research
- The hamlet of Dutjen above Valendas offers a very good overview of the entire landslide area ; the narrow road was renewed a few years ago (also on foot, about an hour from Valendas). Approval is required for access via Riein .
- A mountain hike on the Cassonsgrat , either from the east over the Flimserstein , from the south from the Naraus mountain railway station , or from the west over the Segneshütte, can reach the edge of the landslide.
- The Rhaetian Railway and the Glacier Express travel through the Ruinaulta with just a few tunnels . There are three stops right on the Vorderrhein in the gorge: Trin , Versam-Safien train station and Valendas- Sagogn . The gorge is only selectively accessible by car, there are hardly any parking spaces.
- The route of the Vorderrhein through the Rhine Gorge can be hiked on about two thirds of the route. There is no continuous footpath, but it is being planned. Except for mountaineers, some points of the gorge are inaccessible.
- In Conn, which is located in the Flims forest and thus on the actual debris cone, the spectacular Il spir viewing platform “floats” over the steep face . Conn can be reached on foot or by mountain bike from Flims or Laax. In the forest you come across the Conn-Bächli , a historic irrigation canal (similar to the Valais Suonen ), which supplies the Conn meadow in the otherwise waterless large forest with water for cultivation.
- In Versam there are two viewpoints at Aleschg and Islabord in the area of the landslide, further views are possible from the road to Bonaduz.
- Between Laax and Sagogn below Sogn Giacun Sut , a view of the Ual da Mulin, which is dug deep into the bursting mass, is possible.
- For experts in whitewater, the passage on the Vorderrhein is possible. Various providers offer dinghy rides through the gorge.
In 2016 the Flims Rockslide Association was founded and supported by the municipality of Flims with a contribution.
literature
- Albert Heim: The old landslide in Flims. In: 18th yearbook of the Swiss Alpine Club . 1882-1883, pp. 295-309.
- Albert Heim: Landslide areas in Switzerland, profiles. Maps. Art Institute JC Müller, Dept. Kartogr. Hofer, Zurich 191x. (Nebis)
- G. Hartung: The old landslide area of Flims. In: Journal of the Society for Geography. 19, Berlin 1884.
- Julius Weber: club leader; Geological walks through Switzerland (II). 1913, pp. 162-173.
- G. Deplazes, FS Anselmetti, I. Hajdas: Lake sediments deposited on the Flims rockslide mass: the key to date the largest mass movement in the Alps. In: Terra Nova. 19, 2007, pp. 252-258.
- Gaudenz Deplazes: Lake sediments on the Flims rockslide mass: a new approach to dating the greatest mass movement in the Alps (~ 9490 - 9460 cal. Y BP). Flims / Laax, Graubünden. Thesis. ETH Zurich, 2005, OCLC 637581438 .
- Emil Kirchen: When the mountain falls: the landslide area between Chur and Ilanz. Terra Grischuna Verlag, Chur 1993, ISBN 3-7298-1087-1 .
- YP Bonanomi et al: On the hydrogeology of the landslide area in the Flims area. (= Geological reports. No. 17). State hydrology and geology, Bern 1994, DNB 951031724 .
- Carl Bieler: When the mountain came down. In: Migros magazine. 2006.
- S. Ivy-Ochs, A. v. Poschinger, HA Synal, M. Maisch: Constraining the temporal distribution of giant landslides in the Alps through cosmogenic nuclides: The Flimser Bergsturz. In: Geophysical research abstracts. 7, 2005.
- A. v. Poschinger, U. Haas: The Flims landslide, but a warm-time event? In: Bull Angew. Geology. 2/1, 1997, pp. 35-46.
- A. v. Poschinger: The Flims rockslide as a dam. In: Bull. Angew. Geology. 10/1, 2005, pp. 33-47.
- A. v. Poschinger: Further findings and further questions about the Flims rockslide. In: Bull. Angew. Geology. 11/2, 2006, pp. 35-43.
Web links
- Internet presence of the Flims rockslide association
- Andreas von Poschinger, Ulrich Haas: The Flims rockslide, but a warm-time event?
- Regiun.ch
- Flims rockslide
Individual evidence
- ↑ Administrative accounts of the municipality of Flims 2016