Sturzstrom

A Sturzstrom (from the German Sturz (fall) and Strom (stream, flow)) or rock avalanche is a large landslide, consisting of soil and rock. It travels a great horizontal distance (as much as 20 or 30 times), compared to its initial vertical drop.^[1] Sturzstroms have similarities to the flow of 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.

The Mount St. Helens landslide was a sturzstrom.^{[citation needed]} The slide took place on the north face, and created the valley-like gap seen here.

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 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 friction and allow the mass to travel great distances.^[8] Another theory involves air pockets forming under the slide and providing a cushion that the slide rides over with very low friction, 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 suggests that tiny contact points between bits of ice debris may heat up considerably during the movement, causing melting and forming a more fluid – and thus less friction-limited – mass of material.^[5]

Köfelsite (impactite or frictionite), Köfels Structure, Austria. The 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 much more horizontal ground than downward-sloped ground. Its momentum can even carry the sturzstrom up small hills.^[9] The process of detachment, movement and deposition of a sturzstrom can be recorded by seismometers tens of kilometers away. The peculiar characteristics of this seismic signal make it distinguishable from that of small earthquakes.^[10] In the large Köfels landslide, which flowed into the Ötztal valley in Tyrol, Austria, deposits of fused rocks, called "frictionite" (or "impactite", 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.^[11][12]

See also

• Slump
• Rockslide
• Pyroclastic flow

References

1. Hermanns, Reginald (2013-01-01), "Rock Avalanche (Sturzstrom)", Encyclopedia of Natural Hazards, Encyclopedia of Earth Sciences Series, p. 875, doi:10.1007/978-1-4020-4399-4_301, ISBN 978-90-481-8699-0, 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...5.3417L. doi:10.1038/ncomms4417. PMID 24595169.
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 Geoscience. 5 (8): 574–578. Bibcode:2012NatGe...5..574S. doi:10.1038/ngeo1526.
5. 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, pp. 87–91
8. Collins, G.S.; Melosh (2003). "Acoustic Fluidization and the Extraordinary Mobility of Sturzstroms". Journal of Geophysical Research: Solid Earth. 108. doi:10.1029/2003JB002465. hdl:10044/1/11550. S2CID 6215996.
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. 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. S2CID 133681894.
11. Erismann, T.H. (1979). "Mechanisms of Large Landslides". Rock Mechanics. 12 (1): 15–46. Bibcode:1979RMFMR..12...15E. doi:10.1007/BF01241087. S2CID 129570220.
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.