The extremely long-runout Komansu rock avalanche in the Trans Alai range, Pamir Mountains, southern Kyrgyzstan

Abstract

The nal publication is available at Springer via http://dx.doi.org/10.1007/s10346-014-0492-y Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Massive rock avalanches form some of the largest landslide deposits on Earth and are major 16 geohazards in high-relief mountains. This work reinterprets a previously-reported glacial deposit in 17 the Alai Valley of Kyrgyzstan as the result of an extremely long-runout, probably coseismic, rock 18 avalanche from the Komansu River catchment. Total runout of the rock avalanche is ~28 km, 19 making it one of the longest-runout subaerial non-volcanic rock avalanches thus far identified on 20Earth. This runout length appears to require a rock volume of ~20 km 3 ; however the likely source 21 zone in the Trans Alai range likely contained just ~4 km 3 of rock and presently the deposit has a 22 volume of only 3-5 km 3 ; a pure rock avalanche volume of > 10 km 3 is therefore impossible, so the 23 event was much more mobile than most non-volcanic rock avalanches. Explaining this exceptional 24 mobility is crucial for present day hazard analysis. There is unequivocal sedimentary evidence for 25 intense basal fragmentation, and the deposit in the Alai valley has prominent hummocks; these 26 indicate a rock avalanche rather than a rock-ice avalanche origin. The event occurred 5000-11000 yr 27 B.P., after the region's glaciers had begun retreating, implying that supraglacial runout was limited. 28Current volume -runout relationships suggest a maximum runout of ~10 km for a 4 km 3 rock 29 avalanche. Volcanic debris avalanches, however, are more mobile than non-volcanic rock avalanches 30 due to their much higher source water content; a rock avalanche containing a similarly high water 31 content would require a volume of about 8 km 3 to explain the extreme runout of the Komansu event. 32

The extreme mobility of debris avalanches: A new model of transport mechanism

“…Our results herein concern mainly the inner parts of the granular mass column, but our observations at site 10 (the base of a deposit) show that the particles are more mature (higher rounding and smoothness), whereas some studies on debris avalanches in other places suggest a more intense crushing within the sole of debris avalanche deposits [ Robinson et al , ]. In the case of La Réunion Island, we assume that the spreading of the granular mass in the last stages of the flow [ Bret et al , ; Perinotto , ] results of a substantial loose of topographic confinement with subsequent decrease of the thickness of the flow and resulting lithostatic confinement.…”

Two early Holocene rock avalanches in the Bernese Alps (Rinderhorn, Switzerland)

“…1 and 3)does not show evidence of glacial modification, we assume that by the time of failure (9.8 ka), the Schwarz Glacier had already retreated behind this extent (see alsoIvy-Ochs et al, 2009b). The presence of hummocks and thick deposits in the proximal Arvenwald region supports the absence of ice within the deposit area(Robinson et al, 2014).…”

Collapse of Granular Columns With Fractal Particle Size Distribution: Implications for Understanding the Role of Small Particles in Granular Flows

“…Dry rock avalanches usually happen in the mountainous regions. These granular flows are among the most dangerous natural disasters and can cause extensive damages to the engineering structures because of their powerful ability to move freely from their sources and destructive impact energy (Aaron & Hungr, 2016;Robinson et al, 2015). Various mechanisms have been proposed to explain the extremely large flow mobility that particle flows exhibit, such as entrapped air fluidization (Kent, 1966), air cushion theory (Shreve, 1968), dust dispersion fluidization (Hsü, 1975), fluidization caused by acoustic energy (Collins & Melosh, 2003;Melosh, 1979), lubrication by liquefied saturated soil (Hungr & Evans, 2004), size segregation (Iverson et al, 2010;Roche et al, 2011), self-lubrication by molten rock at the base (De Blasio & Elverhøi, 2008;Goren & Aharonov, 2007), and dynamic rock fragmentation (Davies et al, 2010;Langlois et al, 2015).…”