Emplacement mechanisms of pyroclastic density currents: insights from numerical simulation of dense granular flow with pore gas pressure
Laurent Chupin1,Thierry Dubois 1, Olivier Roche2
Affiliations: 1Laboratoire de Mathématiques Blaise Pascal, Université Clermont Auvergne, CNRS, Clermont-Ferrand, France; 2Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, France
Presentation type: Talk
Presentation time: Friday 14:30 - 14:45, Room R380
Programme No: 3.9.2
Abstract
^The dense basal part of pyroclastic density currents (PDCs) is made up of rock fragments, ash and hot gas. These granular flows behave like fluids and can travel distances of several tens of kilometres on almost horizontal slopes. A better understanding of the physics and mechanisms controlling PDCs emplacement is a major challenge in volcanology. We propose a dense fluidized granular flow model that takes into account the pressure of the interstitial gas. A key point is that the model is two-dimensional, which permits us to investigate the internal dynamics of the flow and in particular the spatio-temporal variation of the interface separating the deposit and the overlying moving layer. This two-dimensional model is based on the equations of conservation of mass and momentum with the µ(I) rheology. We consider the configuration of the sudden release of a dense fluidized granular column and compare our results with those of laboratory experiments. The numerical simulations recover the main characteristics of these flows, namely the shape of the granular mass during collapse, the temporal evolution and speed of the front, and the internal dynamics. In particular, the position of the interface betweenthe basal deposit and the overlying moving layer is captured with accuracy. The interface migrates towards the surface as the granular material spreads and until the mobile granular layer is consumed. The use of a non-averaged model is essential to recover this particular behaviour. ^