An analysis of rheological models for lahar modelling with Iber

Lahars are destructive volcanic debris flows, composed of water and pyroclastic material, capable of traveling long distances at high velocities. Modelling their dynamics is critical for hazard assessment and risk mitigation, yet it remains complex due to factors such as parameter uncertainty, limited calibration data, and variable terrain topography. Current modelling approaches range from empirical methods to advanced depth-averaged numerical simulations, where flow resistance is typically represented through rheological models. Common formulations include the Manning equation, Voellmy friction model, and Bingham plastic rheology, each capturing different aspects of non-Newtonian flow behaviour. This study evaluates the performance of several rheological models in reconstructing the 2001 lahar event at Popocatépetl volcano (Mexico) using the enhanced non-Newtonian module of the Iber hydrodynamic modelling tool (Iber-NNF). Results show that model choice significantly affects simulation accuracy. Manning-like models performed poorly, highlighting the limitations of velocity-dependent resistance terms in capturing static flow behaviour.