At the Cascadia Margin accretionary prism along the coasts of Oregon, Washington, and British Columbia, direct measurements of fluid discharge rates from vent sites indicate flow rates 3-6 orders of magnitude greater than those predicted by local porosity reduction in accreting sediments. This award will evaluate two possible solutions to this discrepancy: fluid migration from depth along a fault zone or near surface seawater recharge due to density-driven flow. Migration along a fault zone will be evaluated through discharge tests to be performed on boreholes drilled into the accretionary prism by the Ocean Drilling Program. Surface recharge will be evaluated by measuring in situ permeability around active vents on the margin. The field portion of this project will utilize the research submersible Alvin.