Transient hydrogeologic models for submarine flow in volcanic seamounts: 1. The Hawaiian Islands

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Abstract
Seamounts and volcanic islands are regions of the seafloor where pressure gradients, caused by temperature variations, are large enough to drive fluid flow. Compaction in surrounding sedimentary aprons, formed during mass wasting of these features, drives fluid flow as well. In seamount environments a complex flow pattern evolves as effects of compaction and free convection interact. We use transient finite element modeling to explore fluid flow and pore pressure in a volcanic edifice and its surrounding sedimentary apron to determine the hydrogeologic and pore pressure regime. Models are based on geophysical cross sections of the Hawaiian Islands and include the volcanic edifice, sedimentary apron, and underlying oceanic crust. Models simulate growth of the volcanic island, flexure of the oceanic crust due to loading, and formation of the sedimentary apron. High sedimentation rates of up to 1 mm/yr during volcanic building cause compaction in the sedimentary apron, and the weight of the edifice compacts the pelagic sediment beneath it; compaction‐driven flow dominates flow patterns. Excess pore pressures are highest during the beginning of volcanic construction and decline through the remainder of the simulation. As sedimentation decreases, compaction‐driven and buoyancy‐driven flow both control flow patterns. When sedimentation stops, pore pressure dissipates, and buoyancy‐driven flow dominates the flow regime. Pore pressure ratios indicate that under certain parameter conditions, pore pressure may exceed lithostatic, leading to unstable edifice conditions. Although fluid velocities are small (q < 0.5 cm/yr), the hydrologic regime has important implications for slope stability, volcanic spreading, sedimentation processes, and geochemical transport.