Dedicated to the memory of our colleague Lorenz Keim, PhD, who died in a snow avalanche on 4 February 2012.
Two-layer scree/snow-avalanche triggered by rockfall (Eastern Alps): Significance for sedimentology of scree slopes
Article first published online: 23 DEC 2013
© 2013 The Authors. © 2013 International Association of Sedimentologists
Volume 61, Issue 4, pages 996–1030, June 2014
How to Cite
Sanders, D., Widera, L., Ostermann, M. (2014), Two-layer scree/snow-avalanche triggered by rockfall (Eastern Alps): Significance for sedimentology of scree slopes. Sedimentology, 61: 996–1030. doi: 10.1111/sed.12083
- Issue published online: 16 MAY 2014
- Article first published online: 23 DEC 2013
- Accepted manuscript online: 10 OCT 2013 10:13AM EST
- Manuscript Accepted: 7 OCT 2013
- Manuscript Revised: 23 AUG 2013
- Manuscript Received: 22 JAN 2013
- scree slope;
- snow avalanche
Rockfalls that trigger scree-laden snow avalanches are common in mountain ranges, but the resulting avalanche development and its role in understanding the sedimentology of scree slopes are rarely described in detail. On Riepenwand (2774 m above sea-level, Kalkkögel range, Alps), on 6 May 2011 a 5800 m3 rockfall of dolostone detached from the flank of a gorge in the upper part of the mountain. After first collapsing into the gorge, the fragmented rock mass fell down freely for 150 m onto a talus covered by coarse-granular snow. Rockfall impact triggered a medium-scale avalanche that developed: (i) a lower layer A of entrained, pure snow; and (ii) an upper layer B of clay-sized to boulder-sized fragments mixed with snow. This ‘two-layer scree/snow avalanche’ halted in the distal slope segment of the talus. Boulders within layer B mainly came to rest in the distal part of the avalanche deposit. Fragments smaller than cobble-size grade did not show obvious downslope segregation. With snowmelt, the rockfall fragments dispersed in layer B were concentrated to a clast-supported veneer that was draped over the older talus surface upon slower melting of avalanche layer A. In the grain-size fraction ≤16 mm, a mean of 5 wt% matrix (silt-sized to clay-sized grains) of the rockfall-derived scree of layer B is similar to a mean matrix content of 7 wt% within stratified talus slopes of the Kalkkögel range. This similarity suggests that a major share of matrix – widespread in stratified talus – stems from rockfalls. The characteristics of the scree veneer as melt-lag of a scree-laden snow avalanche will be blurred with time. Fossil talus successions may contain a substantial proportion of scree carried down by snow avalanches. The formation of a distinct sedimentary facies of snow avalanche-deposited scree is impeded by processes of redeposition and deposit modification on talus.