IMEX_SfloW2D 1.0: a depth-averaged numerical flow model for pyroclastic avalanches

Abstract

Abstract. Pyroclastic avalanches are a type of granular flow generated at active volcanoes by different mechanisms, including the collapse of steep pyroclastic deposits (e.g., scoria and ash cones), fountaining during moderately explosive eruptions, and crumbling and gravitational collapse of lava domes. They represent end-members of gravity-driven pyroclastic flows characterized by relatively small volumes (less than about 1 Mm3) and relatively thin (1–10 m) layers at high particle concentration (10–50 vol %), manifesting strong topographic control. The simulation of their dynamics and mapping of their hazards pose several different problems to researchers and practitioners, mostly due to the complex and still poorly understood rheology of the polydisperse granular mixture and to the interaction with the complex natural three-dimensional topography, which often causes rapid rheological changes. In this paper, we present IMEX_SfloW2D, a depth-averaged flow model describing the granular mixture as a single-phase granular fluid. The model is formulated in absolute Cartesian coordinates (whereby the fluid flow equations are integrated along the direction of gravity) and can be solved over a topography described by a digital elevation model. The numerical discretization and solution algorithms are formulated to allow for a robust description of wet–dry conditions (thus allowing us to accurately track the front propagation) and an implicit solution to the nonlinear friction terms. Owing to these features, the model is able to reproduce steady solutions, such as the triggering and stopping phases of the flow, without the need for empirical conditions. Benchmark cases are discussed to verify the numerical code implementation and to demonstrate the main features of the new model. A preliminary application to the simulation of the 11 February pyroclastic avalanche at the Etna volcano (Italy) is finally presented. In the present formulation, a simple semi-empirical friction model (Voellmy–Salm rheology) is implemented. However, the modular structure of the code facilitates the implementation of more specific and calibrated rheological models for pyroclastic avalanches.

Tree‐Branching‐Based Enhancement of Kinetic Energy Models for Reproducing Channelization Processes of Pyroclastic Density Currents

“…Because of the intrinsic difficulties to properly constrain this parameter, this represents a further, relevant strength of this strategy for application purposes. Finally, we remark that branching energy cone model results are also consistent with other numerical tools, such as FLOW3D (Sheridan et al, 2004) and IMEX_SfloW2D (de' Michieli Vitturi et al, 2019).…”

Major explosions and paroxysms at Stromboli (Italy): a new historical catalog and temporal models of occurrence with uncertainty quantification

“…We report the average rates in the last 10 and 25 years for comparison. www.nature.com/scientificreports/ hot avalanches 63,121,127,131 . Similarly, specific vulnerability functions should be introduced for the main hazardous actions considered 29,128 .…”

“…In future analyses, we plan to introduce in the assessment the spatial component of risk exposure, for example by considering the maximum range of ballistic projectiles, their radial direction, and the spatial density of the projectiles 46 , 65 , 66 or the volume, direction and mechanisms of propagation of pyroclastic density currents and hot avalanches 63 , 121 , 127 , 131 . Similarly, specific vulnerability functions should be introduced for the main hazardous actions considered 29 , 128 .…”

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

“…A common approach to studying the subsequent PDC dynamics and their hazard is to adopt homogeneous mixture, depth-averaged models, which have the advantage of a fast numerical solution (e.g. Patra et al 2005;Shimizu et al 2017;de' Michieli Vitturi et al 2019). However, single-layer models always impose a dichotomy (and the need for a choice) between dominantly frictional (concentrated) or dominantly inertial (dilute) PDCs.…”