The eastern flank of the Juan de Fuca spreading ridge is among the best studied sites for understanding crustal hydrothermal processes in a ridge-flank environment. The researchers seek to resolve primary questions about this hydrogeologic system through the installation of new geophysical and geochemical monitoring equipment during a summer 2004 expedition of the Integrated Ocean Drilling Program (IODP) and through later submersible visits to the borehole observatories to download data and recover fluid samples. To monitor pressure and temperature, CORKs that permit isolation of multiple zones within the formation will be deployed in two existing Juan de Fuca boreholes and a new IODP borehole. The data acquired in these closely-spaced boreholes will constrain the three-dimensional hydrogeologic structure of highly hetereogeneous and fractured oceanic crust. Following the CORK installations in mid-2004, the researchers will use a submersible platform to retrieve data and fluid samples during visits in 2005 and 2007. During these submersible operatins, data will also be downloaded from 3 other existing CORKs in the area (ODP holes 1024C, 1025C, and 857D).