Sturzstrom

The Mt St Helens landslide was a sturzstrom. The slide took place on the north face, and created the valley-like gap seen here.

The term sturzstrom, German word composed of Sturz (fall) and Strom (stream), indicates some large landslides consisting of soil and rock which have a great horizontal movement when compared to its initial vertical drop — as much as 20 or 30 times the vertical distance. The term is used as a synonym to rock avalanche.[1] Sturzstroms have similarities to the flow in glaciers, mudflows, and lava flows. They flow across land fairly easily, and their mobility increases when volume increases.[2][3] They have been found on other bodies in the Solar System, including the Moon, Mars, Venus, Io, Callisto, Iapetus,[4][5] and Phobos.

Movement

A satellite image of the Köfels landslide showing the debris which flowed into the Ötztal valley. It is estimated that around 3 km3 of material were displaced during this slide about 9800 ± 100 years ago.[6][7]

Sturzstroms may be triggered, similarly to other types of landslides, by heavy rains, earthquakes, or volcanic activity. They move rapidly, but do not necessarily require water to be present within them to move, and there is no definite explanation for their kinematic characteristics. One theory, the acoustic fluidization theory, hypothesizes that vibrations caused by the collisions among the rock fragments reduce the overall available friction in the slide and allow the mass to travel much greater distances.[8] Another theory involves air pockets forming under the slide and providing a cushion that the slide rides over to generate its long run-out distances, although the merit of this theory has been called into question by the presence of sturzstroms in vacuums such as on the Moon and Phobos.

Observation of slides on Iapetus suggest that tiny contact points between bits of ice debris may heat them up considerably, causing melting and forming a more fluid — and thus less friction-limited — mass of material.[5]

Köfelsite (impactite or frictionite), Köfels Structure, Austria. Sample is 4.1 cm (1.6 in) wide.

The amount of energy in a sturzstrom is much higher than in a typical landslide. Once moving, it can ride over nearly any terrain and will cover more horizontal ground than downward-sloped ground. Its momentum can even carry it up small hills.[9] The process of detachment, movement and deposition of the landslide mass can be recorded by seismometers tens of kilometers away as a small earthquake.[10] In the large Köfels landslide, which flowed into the Ötztal valley in Tyrol, Austria, deposits of fused rocks, called "frictionite" or "hyalomylonite", were found in the landslide debris. This has been hypothesized to be volcanic in origin or the result of a meteorite impact, but the leading hypothesis is that it was due to the large amount of internal friction. Friction between static and moving rocks can create enough heat to fuse rocks to form frictionite (hyalomylonite).[11][12]

See also

References

  1. ↑ Hermanns, Reginald (2013-01-01), Rock Avalanche (Sturzstrom), pp. 875–875, retrieved 2018-06-21
  2. ↑ Scaringi, Gianvito; Hu, Wei; Xu, Qiang; Huang, Runqiu (2018-01-26). "Shear-Rate-Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels". Geophysical Research Letters. 45 (2): 766–777. Bibcode:2018GeoRL..45..766S. doi:10.1002/2017gl076214. ISSN 0094-8276.
  3. ↑ Lucas, Antoine; Mangeney, Anne; Ampuero, Jean Paul (2014-03-04). "Frictional velocity-weakening in landslides on Earth and on other planetary bodies". Nature Communications. 5: 3417. Bibcode:2014NatCo...5E3417L. doi:10.1038/ncomms4417.
  4. ↑ Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.; Moore, Jeffrey M. (29 July 2012). "Massive ice avalanches on Iapetus mobilized by friction reduction during flash heating". Nature.
  5. 1 2 Palmer, Jason (29 July 2012). "Saturn moon Iapetus' huge landslides stir intrigue". BBC News. Retrieved 2012-07-29.
  6. ↑ Ivy-Ochs S, Heuberger H, Kubik PW, Kerschner H, Bonani G, Frank M, and Schlüchter C. (1998). The age of the Köfels event — relative, 14C, and cosmogenic isotope dating of an early Holocene landslide in the central Alps (Tyrol, Austria). Zeitschrift für Gletscherkunde und Glazialgeologie, (34):57–70.
  7. ↑ Kurt Nicolussi, Christoph Spötlb, Andrea Thurnera, Paula J. Reimer (2015). Precise radiocarbon dating of the giant Köfels landslide (Eastern Alps, Austria), Geomorphology, Volume 243, August 2015, Pages 87–91
  8. ↑ Collins, G.S.; Melosh. "Acoustic Fluidization and the Extraordinary Mobility of Sturzstroms" (PDF).
  9. ↑ Hsü, Kenneth J. (1975). "Catastrophic Debris Streams (Sturzstroms) Generated by Rockfalls". Geological Society of America Bulletin. 86 (1): 129–140. Bibcode:1975GSAB...86..129H. doi:10.1130/0016-7606(1975)86<129:CDSSGB>2.0.CO;2. Retrieved 2017-09-24. Sturzstroms can move along a flat course for unexpectedly large distances and may surge upward by the power of their momentum.
  10. ↑ Fan, Xuanmei; Xu, Qiang; Scaringi, Gianvito; Dai, Lanxin; Li, Weile; Dong, Xiujun; Zhu, Xing; Pei, Xiangjun; Dai, Keren (2017-10-10). "Failure mechanism and kinematics of the deadly June 24th 2017 Xinmo landslide, Maoxian, Sichuan, China". Landslides. 14 (6): 2129–2146. doi:10.1007/s10346-017-0907-7. ISSN 1612-510X.
  11. ↑ Erismann, T.H. (1979). "Mechanisms of Large Landslides". Rock Mechanics. 12 (1): 15–46. Bibcode:1979RMFMR..12...15E. doi:10.1007/BF01241087.
  12. ↑ Weidinger JT, Korup O (2008). "Frictionite as evidence for a large Late Quaternary rockslide near Kanchenjunga, Sikkim Himalayas, India — Implications for extreme events in mountain relief destruction". Geomorphology. 103 (1): 57–65. Bibcode:2009Geomo.103...57W. doi:10.1016/j.geomorph.2007.10.021.
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