This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Friday, February 25, 2011

Do they fly like carpets or flow like a rivers? Blackhawk, Elm, and other Sturzstroms (rock slides)

The Blackhawk slide, California
Photo by Kerry Sieh
17,000 years ago, a mass of marble and limestone slid down out of the San Bernadino Mountains in California, roaring out across the desert, perhaps going airborne like a flying carpet! Known as the Blackhawk Landslide, this is perhaps the most famous example of a group  slides that have exceptionally long runout (travel) distances. Shreve (reference below)

Such landslides are not common, but occur frequently enough that there are some eyewitness accounts.  One such slide was the Elm rockfall in Switzerland in 1881.  It buried a village and killed 115 people.  This event was described in German by Albert Heim* and in English by Ken Hsu**.  (If anyone knows of an English translation of Heim's work, I would much appreciate a copy!!)

One eyewitness of the Elm slide described the airborne trajectory:

"Then I saw the rockmass jump away from the ledge. The lower part of the block was squeezed by the pressure of the rapidly falling upper part, became disintegrated and burst forth into the air. .. The debris shot with unbelievable speed northward toward the hamlet of Untertal and over and above the creek, for I could see the alder forest by the creek under the stream of shooting debris."

Hsu suggested that the word "sturzstrom", which literally means "fallstream" be adopted to describe these slides and that it be defined as "a stream of very rapidly moving debris derived from the disintegration of a fallen rock mass of very large size; the speed of a sturzstrom often exceeds 100 km/hr, and its volume is commonly greater than a million cubic meters."

In spite of the geologic evidence and eyewitness accounts, there is still no general agreement about the mechanism by which the sturzstroms achieve their long runout distances. Shreve (1968) proposed that the avalanches floated over a layer of compressed air; Goguel (1978) proposed that a layer of steam generated by friction allowed the great mobility;   Erismann (1979) proposed that friction allowed melting; others (Fineburg, Bagnold, McSaveney, Campbell) proposed various mechanisms related to the behavior of granular flow. Melosh proposed an acoustic fluidization model, in which  high-frequency (acoustic) fluctuations in the local pressure around grains relieved the overburden pressure, allowing the material to move even in the absence of a large driving pressure. There is a good tutorial about acoustic fluidization here, the source of the numbered references below. It is possible that different mechanisms operate in different parts of the landslide trajectory.

See also this post for more discussion of big landslides.

Shreve, R.L. 1968,The Blackhawk landslide: Geol. Soc. America Special Paper 108, 47 pp.
Sreve, R.L., 1966, Sherman landslide, Alaska: Science, 154, p. 1639-1643.

*Heim, Albert, 1882, Der Bergsturz von Elm: Deutsch.Geol. Gesell. Zeitschr., v. 34, p. 74-115, and/or Buss, E., and Heim, Albert, 1881, Der Bergstruz von Elm: Zurich, Wurster and Cie, 163 p., and/or Heim, Albert, 1882, Bergsturz and Menschenleben: Zurich, Fretz and Wasmuth Verlag, 218 p.

**Hsu, Kenneth, Catastrophic Debris Streams (Sturzstroms) Generated by Rockfalls, Geological Society of America Bulletin, v. 86, p. 129-140, 1975.

  1. Goguel, J. (1978) Rockslides and Avalanches, Edited by B. Voight, 1, 693-705, Elsevier, Amsterdam.
  2. Erismann, T. H. (1979) Rock Mechanics, 12, 15-46.
  3. Fineburg, J. (1997) Nature, 386, 323-324.
  4. Bagnold, R. A. (1956) Philosophical Transactions of the Royal Society of London, A, 225, 49-63.
  5. McSaveney, M. J. (1978) Rockslides and Avalanches, Edited by B. Voight, 1, 197-258, Elsevier, Amsterdam.
  6. Campbell, C. S. (1990) Ann. Rev. Fluid Mech., 22, 57-92.
  7. Iverson, R. M. (1997) Rev. Geophysics, 35, 245-296.
  8. Melosh, H. J. (1979) JGR, 84, 7513-7520.
  9. Melosh, H. J. (1987) Debris Flows/Avalanches: Process, Recognition and Mitigation, edited by J. E. Costa and G. F. Wieczorek, 41-49, GSA.

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