A FLUID-ROCK INTERACTION CELLULAR-AUTOMATON OF VOLCANO MECHANICS - APPLICATION TO THE PITON DE LA FOURNAISE

We developed a cellular automata model of fluid circulation within a r ock matrix to test whether considering a volcano as a complex system h elps understand the observed eruptive and seismicity patterns of the P iton de la Fournaise (PF) volcano. In this model; fluid and rock cells interact through locally defined rules, including a steady increase o f pressure, a threshold dynamics, a fluid redistribution algorithm, an d an energy dissipation process. Comparison of the model results and o bservations for more than 40 simulations provides information on the m echanics of the PF volcano and basaltic volcanoes in general. First, w e demonstrate that the multiple lenses magma storage model for the sum mit reservoir of basaltic volcanoes is consistent with the PF 1920-199 2 eruptive pattern, proposing an alternative to the macrochamber model . Second, we show that the great number of interactions between magma storage lenses in a critical state may work as a nonlinear filter, mod ifying a possible uniform increase of pressure in the input, induced b y deep magma supply and gas exsolution during crystallization, into a nonlinear fluid flow emergence in time and size, both unpredictable an d organized in nonrandom scaling statistics. The fluid-rock cellular a utomaton allows us to explore scales ranging from global Earth mantle to porous rock matrix, thus rationalizing the power law volume distrib ution of total eruptions on the Earth surface [Me Clelland et al., 198 9] and the hierarchical organization that is reported for many types o f fluid-induced seismicity [Grasso, 1993; Miller et at, 1996], respect ively.