Physical modeling of small-volume pyroclastic flows

Abstract:

Small-volume pyroclastic flows represent common hazardous phenomena generated by the repetitive partial collapse of a growing lava-dome. Their fluid-like behavior can be reproduced using fluidization techniques, commonly used in industrial systems, which lead to the formation of homogeneous particulate suspensions that can be represented as an equivalent fluid of similar density and viscosity. We present here a simplified physical model based on shallow-water equations. The mixture is approximated as aninviscid fluid that moves as a plug flow that thins during propagation by sedimentation with negligible energy dissipation. The runout duration is controlled by the time taken to the particles to settle during transport. We present here an operational model based on one-dimensional numerical simulations performed using a finite volume scheme. When compared to laboratory experiments involving the dam-break flows of particulate suspensions, the model proves to be capable of consistently reproducingthe first-order feature of these flows. While the extension to natural cases is not obvious, especially because of the lack of available measurements of the key parameters from field analyses, simulations allow to recover the relevant order of magnitude for both the runout distance and duration, as well as it is able to provide consistent deposit morphologies.

Keywords : Pyroclastic flows, numerical model, particulate suspensions, fluidization, scaling laws.