{"id":{"repo_id":"ethz","oai_identifier":"oai:www.research-collection.ethz.ch:20.500.11850/802796"},"canonical_url":"https://search.dev.ndltd.org/etd/ethz/oai:www.research-collection.ethz.ch:20.500.11850/802796","repository":{"repo_id":"ethz","name":"ETH Zürich","base_url":"https://www.research-collection.ethz.ch/oai/request"},"display":{"title":"On mechanics and microstructure of weak snow layers","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["Schöttner, Jakob Wolfram Klaus; id_orcid0000-0002-9031-8885"],"institution":"ETH Zurich","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Schweizer, Jürg; id_orcid0000-0002-9031-8885","van Herwijnen, Alec","Kammer, David S.; id_orcid0000-0002-9031-8885","Freitag, Johannes","Reiweger, Ingrid","Weißgraeber, Philipp"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2026,"date_issued":"2026","date_published":"2026","updated_at":"2026-07-27T19:26:43Z","subjects":["snow mechanics; snow microstructure; snow avalanche formation","Natural sciences"],"languages":["en"],"rights":["info:eu-repo/semantics/openAccess","Creative Commons Attribution 4.0 International"],"rights_urls":["http://creativecommons.org/licenses/by/4.0/"],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.3929/ethz-c-000802796"],"render_values":[{"text":"https://doi.org/10.3929/ethz-c-000802796","href":"https://doi.org/10.3929/ethz-c-000802796","code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/20.500.11850/802796","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Schweizer, Jürg; id_orcid0000-0002-9031-8885","van Herwijnen, Alec","Kammer, David S.; id_orcid0000-0002-9031-8885","Freitag, Johannes","Reiweger, Ingrid","Weißgraeber, Philipp"]},{"key":"dc:creator","label":"Author","values":["Schöttner, Jakob Wolfram Klaus; id_orcid0000-0002-9031-8885"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2026"]},{"key":"dc:publisher","label":"Institution","values":["ETH Zurich"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["snow mechanics; snow microstructure; snow avalanche formation","Natural sciences"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess","http://creativecommons.org/licenses/by/4.0/","Creative Commons Attribution 4.0 International"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/20.500.11850/802796","https://doi.org/10.3929/ethz-c-000802796"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["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.","Trockene Schneebrettlawinen entstehen, wenn eine Schwachschicht in der Schneedecke versagt. Diese lokale Schädigung kann sich in Form eines Risses über einen ganzen Hang ausbreiten und die Verbindung des darüberliegenden Schneebretts zur Unterlage trennen. Ist der Hang ausreichend steil, wird die Reibung an der Bruchfläche überwunden und die Lawine gleitet ab. Die operationelle Vorhersage von Schneebrettlawinen stützt sich derzeit hauptsächlich auf meteorologische Daten und Beobachtungen der Schneedecke. Sie ist demnach weitgehend probabilistisch, ohne das vorhandene Prozessverständnis voll auszuschöpfen. Mechanische Lawinenmodelle bieten die Möglichkeit, die Stabilität der Schneedecke physikalisch fundiert zu bewerten. Dafür sind jedoch Kenntnisse über zuverlässige Materialparameter erforderlich. Da Schnee ein sich ständig veränderndes Geomaterial mit komplexer Mikrostruktur ist, sind dichtebasierte Beziehungen mit großen Unsicherheiten behaftet, insbesondere für dünne und heterogene Schwachschichten. Das zentrale Ziel dieser Arbeit besteht daher darin, mechanische Kennwerte von Schwachschichten genauer einzugrenzen und ihr Verhalten mit ihrer dreidimensionalen Mikrostruktur zu verknüpfen. Dazu kombiniert diese Arbeit umfangreiche Laborversuche mit hochauflösenden Mikro-Computertomographie-Aufnahmen. Die Ergebnisse bestätigen, dass die Dichte der dominierende Einflussfaktor für die mechanischen Eigenschaften von Schnee ist. Gleichzeitig zeigt sich, dass die Mikrostruktur die Dichteabhängigkeit von Steifigkeit und Festigkeit systematisch steuert. Dieses Verhalten lässt sich durch korntypabhängige Skalierungsgesetze in eine pragmatische Form fassen. Ergänzend grenzen kombinierte Druck- und Scherversuche das Versagen unter multiaxialen Spannungszuständen weiter ein. Sie deuten darauf hin, dass sich das Versagen einiger getesteter Schwachschichten durch geschlossene, elliptische Versagenskriterien im Normalspannungs- und Schubspannungsraum beschreiben lässt. Damit liefert die Arbeit praktikable Parametrisierungen, konkretisiert Versagenskriterien für Lawinenmodelle und skizziert nächste Schritte hin zu mikrostruktur-gestützten Stoffmodellen von Schnee."]},{"key":"dc:format","label":"Dc Format","values":["application/application/pdf"]},{"key":"dc:title","label":"Title","values":["On mechanics and microstructure of weak snow layers"]}]}],"canonical_facts":{"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"],"dc:creator":["Schöttner, Jakob Wolfram Klaus; id_orcid0000-0002-9031-8885"],"dc:date":["2026"],"dc:description":["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.","Trockene Schneebrettlawinen entstehen, wenn eine Schwachschicht in der Schneedecke versagt. Diese lokale Schädigung kann sich in Form eines Risses über einen ganzen Hang ausbreiten und die Verbindung des darüberliegenden Schneebretts zur Unterlage trennen. Ist der Hang ausreichend steil, wird die Reibung an der Bruchfläche überwunden und die Lawine gleitet ab. Die operationelle Vorhersage von Schneebrettlawinen stützt sich derzeit hauptsächlich auf meteorologische Daten und Beobachtungen der Schneedecke. Sie ist demnach weitgehend probabilistisch, ohne das vorhandene Prozessverständnis voll auszuschöpfen. Mechanische Lawinenmodelle bieten die Möglichkeit, die Stabilität der Schneedecke physikalisch fundiert zu bewerten. Dafür sind jedoch Kenntnisse über zuverlässige Materialparameter erforderlich. Da Schnee ein sich ständig veränderndes Geomaterial mit komplexer Mikrostruktur ist, sind dichtebasierte Beziehungen mit großen Unsicherheiten behaftet, insbesondere für dünne und heterogene Schwachschichten. Das zentrale Ziel dieser Arbeit besteht daher darin, mechanische Kennwerte von Schwachschichten genauer einzugrenzen und ihr Verhalten mit ihrer dreidimensionalen Mikrostruktur zu verknüpfen. Dazu kombiniert diese Arbeit umfangreiche Laborversuche mit hochauflösenden Mikro-Computertomographie-Aufnahmen. Die Ergebnisse bestätigen, dass die Dichte der dominierende Einflussfaktor für die mechanischen Eigenschaften von Schnee ist. Gleichzeitig zeigt sich, dass die Mikrostruktur die Dichteabhängigkeit von Steifigkeit und Festigkeit systematisch steuert. Dieses Verhalten lässt sich durch korntypabhängige Skalierungsgesetze in eine pragmatische Form fassen. Ergänzend grenzen kombinierte Druck- und Scherversuche das Versagen unter multiaxialen Spannungszuständen weiter ein. Sie deuten darauf hin, dass sich das Versagen einiger getesteter Schwachschichten durch geschlossene, elliptische Versagenskriterien im Normalspannungs- und Schubspannungsraum beschreiben lässt. Damit liefert die Arbeit praktikable Parametrisierungen, konkretisiert Versagenskriterien für Lawinenmodelle und skizziert nächste Schritte hin zu mikrostruktur-gestützten Stoffmodellen von Schnee."],"dc:format":["application/application/pdf"],"dc:identifier":["http://hdl.handle.net/20.500.11850/802796","https://doi.org/10.3929/ethz-c-000802796"],"dc:language":["en"],"dc:publisher":["ETH Zurich"],"dc:rights":["info:eu-repo/semantics/openAccess","http://creativecommons.org/licenses/by/4.0/","Creative Commons Attribution 4.0 International"],"dc:subject":["snow mechanics; snow microstructure; snow avalanche formation","Natural sciences"],"dc:title":["On mechanics and microstructure of weak snow layers"],"dc:type":["info:eu-repo/semantics/doctoralThesis"]},"updated_at":"2026-07-27T19:26:43Z"}