The Development of a Next Generation Subseabed Pore Pressure Insrument for Marine Hydrogeology: The PUPPI-II

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The PIs propose to develop a new subseafloor pore pressure instrument similar to the Pop Up Pore Pressure Instrument (PUPPI) developed by Peter Schultheiss in the eighties. The instrument package consists of an upper command unit attached to a lance and ballast. It is deployed by free-fall from a ship and embeds the lance in the sediment. One or more ports on the lance are connected to a high resolution pressure transducer and the initial insertion pressure pulse, decay, and final equilibrium are recorded along with the bottom pressure. The difference between the equilibrium value and the hydrostatic gradient give the state of over- or underpressure and ultimately the state of stress and nature of fluid flow. The instrument can be left on the bottom for months or years for a continuous record of pressure or can be recovered after reaching equilibrium. An acoustic release mechanism separates the command unit from the lance and ballast and the command unit floats to the surface for recovery. Pore pressure is a fundamental physical parameter for determining the current state of stress and the rate of transport of fluid and energy within the sediment. In spite of this, direct measurements of pore pressure by the marine hydrogeology community have been rare. This has primarily been due to the lack of instrumentation with adequate resolution and other important qualities. Recent advances in various technologies have made such measurements possible and there has been a resurgence of interest for such measurements within the international marine geoscience community. Broader ImpactsDevelopment of the seafloor piezometer will require international collaboration as well as collaboration with industry. As the PIs point out, this instrument could become an integral part of a number of national and international programs (RIDGE, MARGINS, IODP, NEPTUNE), and could be used to address many of the questions that represent the stated goals of these programs. In addition, pore pressure data is valuable for researchers studying problems with societal relevance, such as earthquake responses, gas hydrate formation, and mass wasting events. The proposal includes support for a graduate student in instrument design.