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| Titel |
Slab entrainment and surge dynamics of the 2015 Valleé de la Sionne avalanches |
| VerfasserIn |
Anselm Köhler, Jim McElwaine, Betty Sovilla |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122574
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| Publikation (Nr.) |
 EGU/EGU2016-1637.pdf |
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| Zusammenfassung |
| On 3 February 2015 five avalanches were artificially released at the Valleé de la Sionne test
site in the west of Switzerland. The dense parts of the avalanches were tracked by
the GEODAR Mark 2 radar system at 111 Hz framerate with 0.75 m down slope
resolution.
The data show that these avalanche contain several internal surges and that the avalanche
front is repeatedly overtaken by some of these surges. We show that these surges exist on
different scale. While the major surges originates from secondary triggered slab releases and
occur all over the avalanche. The minor surges are only found in the energetic part of a well
developed powder snow avalanche. The mass of the major surges can be as huge as the initial
released mass, this has a dramatic effect on the mass distribution inside the avalanche and
effects the front velocity and run out. Furthermore, the secondary released snow slabs are an
important entrainment mechanism and up to 50 percent of the mass entered the avalanche via
slab entrainment.
We analyse the dynamics of the leading edge and the minor surges in more detail using a
simple one dimensional model with frictional resistance and quadratic velocity dependent
drag. These models fit the data well for the start and middle of avalanche but cannot capture
the slowing and overtaking of the minor surge. We find much higher friction coefficients to
describe the surging. We propose that this data can only be explained by changes
in the snow surface. These effects are not included in current models yet, but the
data presented here will enable the development and verification of such models. |
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