On mechanics and microstructure of weak snow layers

Dry-snow slab avalanches begin when a buried weak layer fails. This local damage can spread across the slope as a crack, detaching the overlying slab from the snowpack. If the slope is sufficiently steep, basal friction is overcome and the avalanche releases. Forecasting these avalanches remains largely probabilistic, driven by meteorology and snowpack observations, and does not yet fully exploit this process understanding. Mechanical avalanche release models offer a path towards more deterministic stability estimates, but they critically depend on reliable mechanical parameters. Snow is a constantly changing geomaterial with a complex microstructure, so density-based relations leave large uncertainties, particularly for thin and heterogeneous weak layers. The central goal of this thesis is to better constrain mechanical parameters of weak snow layers and to relate their behavior to the three-dimensional microstructure. To achieve this, the thesis combines extensive laboratory experiments with high-resolution micro-computed tomography scans. The results confirm density as the dominant first-order control, but also show that the microstructure systematically influences how stiffness and strength depend on density. Grain-type-dependent scaling laws capture this behavior in a pragmatic form. Combined compression and shear experiments further constrained failure under multiaxial stress states and indicate that, for the tested buried surface hoar weak layers, failure can be described by closed, approximately elliptical envelopes in the shear stress-compressive stress space. These findings provide practical parameterizations and better constrain failure criteria for avalanche release models, while outlining next steps towards a microstructure-informed constitutive description of snow and snow weak layers.

Grantor dc:publisher

ETH Zurich

Year dc:date

2026

Author dc:creator

• Schöttner, Jakob Wolfram Klaus; id_orcid0000-0002-9031-8885

Contributors dc:contributor

• Schweizer, Jürg; id_orcid0000-0002-9031-8885
• van Herwijnen, Alec
• Kammer, David S.; id_orcid0000-0002-9031-8885
• Freitag, Johannes
• Reiweger, Ingrid
• Weißgraeber, Philipp

• snow mechanics; snow microstructure; snow avalanche formation
• Natural sciences

Statement dc:rights

• info:eu-repo/semantics/openAccess
• Creative Commons Attribution 4.0 International

Licence

• http://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.3929/ethz-c-000802796

OAI identifier oai:identifier

oai:www.research-collection.ethz.ch:20.500.11850/802796