A Multi‐Phase Mass Flow Model

Abstract

Geomorphic mass flows are often complex in terms of material composition and its evolution in space and time. The simulation of those hazardous phenomena would strongly benefit from a multi‐phase model, considering the motion and—importantly—interaction of phases characterized by different physical aspects including densities, frictions, viscosities, fractions, and their mechanical responses. However, such a genuine multi‐phase model is still lacking. Here, we present a first‐ever, multi‐mechanical, multi‐phase mass flow model composed of three different phases: the coarse solid fraction, fine‐solid fraction, and viscous fluid. The coarse solid component, called solid, represents boulders, cobbles, gravels, or blocks of ice. Fine‐solid represents fine particles and sand, whereas water and very fine particles, including colloids, silt, and clay, constitute the viscous fluid component in the mixture. The involved materials display distinct mechanical responses and dynamic behaviors. Therefore, the solid, fine‐solid, and fluid phases are described by Coulomb‐plastic, shear‐ and pressure‐dependent plasticity‐dominated viscoplastic, and viscosity‐dominated viscoplastic rheologies. They are supposed to best represent those materials. The new model is flexible and addresses some long‐standing issues of multi‐phase mass flows on how to reliably describe the flow dynamics, runout, and deposition morphology of such type of phenomena. With reference to some benchmark simulations, the essence of the model and its applicability are discussed.

Reconstruction of the 1941 GLOF process chain at Lake Palcacocha (Cordillera Blanca, Peru)

“…In general, the mechanisms of the landslide impact into the lake, which were not the focus of the present study, would require more detailed investigations. Ideally, such work would be based on a three-phase model (Pudasaini and Mergili, 2019; considering ice as a separate phase) and consider knowledge and experience gained from comparable, well-documented events. A possible candidate for such an event would be the 2010 event at Laguna 513, which was back-calculated by Schneider et al (2014).…”

Modelling pyroclastic density currents from a subplinian eruption at La Soufrière de Guadeloupe (West Indies, France)

“…They are more suited to low aspect ratio PDCs, often confined to the volcano flanks, or to describe the behaviour of the basal part of a stratified PDC. Most of the difficulties in the physical description of PDCs is related to the interplay between these two end-members in natural (Druitt et al 2002b;Ogburn et al 2014;Bernard et al 2014;Capra et al 2016) and laboratory PDCs (Breard and Lube 2017), where the multiphase nature of the mixture also poses significant physical and mathematical challenges (Pitman and Le 2005;Pudasaini and Mergili 2019). An attractive and promising alternative to single-layer models is provided by two-layer depth-averaged models (Doyle et al 2010;Kelfoun 2017;Shimizu et al 2019;Gueugneau et al 2019), in which PDC stratification is simplified into a concentrated, basal layer underlying a dilute ash cloud.…”

Versatile image-based measurements of granular flows and water wave propagation in experiments of tsunamis generated by landslides

“…This measurement technique addresses the observation of multiphase mass-flow complex phenomena at high details and versatility. Therefore, it can be employed in experiments to test multi-phase numerical models that are recently receiving a remarkable scientific focus (Pitman and Le 2005;Abadie et al 2010;Cecioni and Bellotti 2010;Montagna et al 2011;Pudasaini 2012Pudasaini , 2014Pudasaini and Mergili 2019;Kim et al 2019).…”