Avalanche formation

In snow-covered mountains, avalanches are a significant natural hazard. They endanger settlements, roads and people who live and recreate in the mountains in winter. We investigate the snow properties and processes at work in the formation of an avalanche and so help to improve avalanche forecasting.

Whether and how avalanches occur depends largely on the structure of the snowpack. Does it consist of many different layers? Are they thick or rather thin? Continuous or patchy? Strong or weak? There are many influencing factors, and some are difficult to measure. To improve avalanche forecasting and to help snow sports enthusiasts better assess the avalanche danger themselves, we investigate how exactly different types of avalanches occur.

Experiments and models

The aim of our research is to better understand the processes that take place before, during and after avalanche release. We use field measurements, laboratory experiments and computer models.

In field experiments we measure properties of the natural snow cover and soil, e.g.:

filming a fracture as it propagates inside a weak layer using high-speed cameras
we measure the stratification and the variability of individual snowpack layers with the SnowMicroPen, a high-resolution snow probe
we measure soil and snow moisture to better understand the formation of glide-snow avalanches.

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Field experiment used to observe fracture propagation through weak snowpack layers. Photo: Alec van Herwijnen, SLF

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Der vergrösserte Ausschnitt aus einem Schneeprofil. Im unteren Drittel zieht sich eine Schwachschicht aus eingeschneiten Oberflächenreifkristallen fast horizontal durch das Profil. In der Bildmitte zieht sich ein senkrechter Riss von oben bis zu der Schwachschicht. Rechts von diesem Riss ist die Schwachschicht noch intakt, die Kristalle stehen aufrecht; links ist die Schicht gebrochen, die Kristalle liegen flach zusammengedrückt. Der Bruch hat sich also von links kommend ausgebreitet (im Bild mit einem roten Pfeil visualisiert). In der Bildmitte ist es zum Zugriss durch das Schneebrett gekommen, so dass der in der Schwachschicht laufende Riss stoppte.

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Weak layer of surface hoar crystals covered by snow. On the right of the picture, the layer is intact; on the left it is fractured. The fracture has propagated in the weak layer from the left. In the centre of the picture, a tensile fracture through the slab has halted the fracture in the weak layer. Image: ASARC/University of Calgary

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Glide cracks and glide-snow avalanches that released on the Dorfberg. Photo: SLF camera

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Glide cracks on the Dorfberg. Photo: Amelie Fees, SLF

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Soil sensors measuring matrix potential (left) and water content (right) at several depths. Photo: Amelie Fees, SLF

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The cold lab allows us to conduct experiments under controlled conditions. Here we have the possibility to:

produce nature-identical snow and grow weak layers ourselves, so that we always work with the same starting material.
Carry out load tests that provide information about the mechanical properties of snow.
use computer tomography to investigate the microstructure of weak layers and derive findings for avalanche forecasting.
study the absorption of water from the soil under controlled conditions.

The results of measurements and experiments are used, among other things, as input for numerical simulations that help us to better understand physical processes, or to optimise the SNOWPACK model used by warning services in a number of countries as a tool for assessing avalanche danger.