Extending Varnes' mass movement classification from pre-failure through post-failure

Traditional landslide classifications, such as those by Varnes (1978) and Cruden & Varnes (1996) are primarily focused on material type and movement style. The new scheme presented here, inspired by Leroueil et al. (1996), organizes mass movements into sequential stages: Pre-failure: Damage and deformation processes that weaken the slope; Failure: The point at which mechanical properties are altered enough to cause instability; Activation: The initial movement triggered by failure; Post-failure: Changes in propagation style or further movement; Quiescence: A period of inactivity, but with potential for remobilization; Remobilization/Reactivation: Renewed movement after quiescence by new types or following the previous movement styles; Stabilization: The final, stable state.

This approach allows for a more nuanced understanding of landslide evolution, supporting both forensic analysis and predictive modeling. The expanded classification explicitly incorporates ice, snow (Locat et al., 2024), and rock debris as distinct material types, recognizing their growing importance in mass movement processes: Ice: Behaves similarly to rock, with unique rheological properties (e.g., ice creep, fracture). Snow: Treated analogously to soil, with subtypes (dry, wet, slush) based on water content and mechanical behavior. Rock debris: Recognized for its distinct propagation and initiation mechanisms, differing from both classical rockslides and debris slides. It also considers the significance of ambient fluid (subaerial vs subaqueous landslides), which has important implications during the pre-failure, failure and post-failure stages as well as cascading events such as tsunamis.

Several new types and refinements are introduced: Damaging: Cohesive masses breaking away in an indefinable manner, not previously formalized; Detachment: A cohesive solid body that separates either through an indeterminate process or by means of tearing. Glide: Solid or cohesive masses slipping over gentle slopes, including phenomena like rock blocks sliding on grassland. Secondary effects: Air blasts, entrainment, and erosion are now explicitly included, acknowledging their significant impact during and after mass movement events.

The classification also clarifies and expands definitions for slides, flows including Flow ± Slide, water-supported and density currents, the latter being specific for subaqueous landslides, snow avalanches and pyroclastic flow, ensuring that a broader range of real-world scenarios are covered.

By structuring landslide classification around stages and integrating new materials and types, the proposed scheme: Facilitates scenario-based hazard and risk assessment; Supports both retrospective (forensic) and predictive analyses; Addresses the increasing complexity of mass movements in a changing climate, including cascading and sequential events.

References

Cruden, D.M., & Varnes, D.J. 1996. Landslide Types and Processes. In: Turner, A.K.S., R.L. (ed.) Landslides: Investigation and Mitigation, 36-75.

Leroueil, S., Locat, J., Vaunat, J., Picarelli, L., Lee, H. & Faure, R. 1996. Geotechnical characterization of slope movements. Proc., 7th International Symposium on Landslides, Trondheim, 53-74.

Locat J., Urgeles R., Isler D., Jaboyedoff M., Lee H., Leroueil S., Mulder T., 2024. The Varnes’ classification of mass movement types to include the subaqueous environment and snow/ice materials. In: Merrien V. and Nicot F. (Eds.): 14TH INTERNATIONAL SYMPOSIUM ON LANDSLIDES, 8th - 12th July 2024, Chambéry, France. 189-192.

Varnes, D.J. 1978. Slope movement types and processes. Special report, 176, 11-33.