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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Short summary
The modern picture of snow slab avalanche release process involves a dynamic crack propagation phase in which a whole slope gets detached. The present work contains the first field methodology which provides the temporal and spatial resolution necessary to study this phase. We demonstrate the versatile capabilities and accuracy of our method by revealing intricate dynamics and present how to determine relevant characteristics of crack propagation such as e.g. crack speed.
Preprints
https://doi.org/10.5194/tc-2020-360
https://doi.org/10.5194/tc-2020-360

  06 Jan 2021

06 Jan 2021

Review status: this preprint is currently under review for the journal TC.

Dynamic crack propagation in weak snowpack layers: Insights from high-resolution, high-speed photography

Bastian Bergfeld1, Alec van Herwijnen1, Benjamin Reuter2, Grégoire Bobillier1, Jürg Dual3, and Jürg Schweizer1 Bastian Bergfeld et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 2Météo-France, CNRS, CNRM, Centre d‘Etudes de la Neige, Grenoble, France
  • 3Institute for Mechanical Systems, ETH Zurich, Zurich, Switzerland

Abstract. To assess snow avalanche release probability, information on failure initiation and crack propagation in weak snowpack layers underlying cohesive slab layers are required. With the introduction of the Propagation Saw Test (PST) in the mid-2000s, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes, including slab bending, weak layer collapse, crack propagation speed and the frictional behavior after weak layer fracture. However, the resolution of the videos and the methodology used did not allow insight into dynamic processes such as the evolution of crack speed within a PST or the touchdown distance, which is the length from the crack tip to the trailing point where the slab sits on the crushed weak layer at rest again. Therefore, to study the dynamics of crack propagation we recorded PST experiments using a powerful portable high-speed camera with a horizontal resolution of 1280 pixels at rates up to 20,000 frames per second. By applying a high-density speckling pattern on the entire PST column, we then used digital image correlation (DIC) to derive high-resolution displacement and strain fields in the slab, weak layer, and substrate. The high frame rates allowed time derivatives to obtain velocity and acceleration fields. On the one hand, we demonstrate the versatile capabilities and accuracy of the DIC method by showing three PST experiments resulting in slab fracture, crack arrest and full propagation. On the other hand, we present a methodology to determine relevant characteristics of crack propagation: the crack speed and touchdown distance within a PST, and the specific fracture energy of the weak layer. To estimate the effective elastic modulus of the slab and weak layer as well as the weak layer specific fracture energy we used a recently proposed mechanical model. A comparison to already established methods showed good agreement. Furthermore, our methodology also provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

Bastian Bergfeld et al.

Status: open (until 03 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Bastian Bergfeld et al.

Video supplement

Crack Propagation in a Propagation Saw Test Bastian Bergfeld https://doi.org/10.5446/50536

Bastian Bergfeld et al.

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Short summary
The modern picture of snow slab avalanche release process involves a dynamic crack propagation phase in which a whole slope gets detached. The present work contains the first field methodology which provides the temporal and spatial resolution necessary to study this phase. We demonstrate the versatile capabilities and accuracy of our method by revealing intricate dynamics and present how to determine relevant characteristics of crack propagation such as e.g. crack speed.
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