Abstract

Mud volcanoes erupt sediment sourced from subsurface, consolidated mudstones via a conductive flow pathway (conduit). A 3 -D seismic survey of mud volcanoes in the Eastern Mediterranean shows localised thinning of the source unit in zones at the base of each conduit, interpreted to result from mud depletion. These depletion zones are typically bowl-shaped, suggesting that they grow radially outward from the base of the conduit. Fluidisation, whereby consolidated sediments can be mobilised by migrating pore fluids of a sufficient velocity, has previously been proposed as a mechanism to explain mud volcano formation. However, the dynamics of fluidisation during eruptions are poorly understood due to limited subsurface observations. We hypothesise that the sudden opening of the conduit initiates rapid fluid expulsion, inducing porous flow through and fluidisation of the source rock. We present a novel theoretical model of flow-driven fluidisation, capturing the dynamic interface between the poroelastic solid and viscous fluidised regions. Our results indicate that fluidisation initiates at the conduit and spreads radially. We show that this problem is mathematically analogous to the unstable melting of a superheated solid. Using asymptotic analysis, we explore the mechanisms that regulate this unstable growth to produce a depletion zone with a characteristic size.