Abstract Volcanic debris avalanches can transform into highly mobile debris flows, reaching long runout distances and posing significant hazards to downstream populations. This high mobility arises from complex, evolving rheological behavior driven by dynamic changes in pore pressure, internal resistance, and material properties during the flow. The 2012 Te Maari flank collapse at Tongariro, New Zealand, triggered a channelized debris avalanche that provides a valuable case study to explore these processes. Our modeling approach uses the depth‐averaged, multiphase numerical model D‐Claw, which captures the dynamic evolution of the material's apparent rheology. We examine the effect of key initial material properties (e.g., hydraulic permeability, compressibility and dilatancy) on the mechanical response of the avalanche at initiation and throughout its transformation into a debris flow. A linear regression analysis based on Te Maari simulations reveals that flow mobility is primarily controlled by hydraulic permeability and its interactions with compressibility and dilatancy, which together drive transitions in flow behavior. Notably, for the Te Maari case study, two contrasting sets of initial parameters (i.e., a low‐permeability and high‐permeability scenario) both accurately reproduce the observed flow runout. This suggests that different mechanical processes can compensate for one another to produce comparable mobility outcomes. These findings enhance our understanding of debris flow dynamics and point toward the need for future modeling approaches to incorporate the coupled, time‐evolving nature of internal material properties.
Vicente et al. (2026) studied this question.