Upon making hydrothermal and hydrological measurements in borehole 504-B during last September and October's leg 69 trip of the Glomar Challenger, researchers found, to their surprise, that cold water from the ocean bottom was flowing into the hole. The water then entered the basement rock in a zone about 80 m wide, beginning at a point about 365 m below the sea floor and 90 m below the sediment/basement interface.

When another team of experimenters reentered the hole 58 days later, during leg 70, they found water still moving down the upper portion of the hole at a rate estimated to be a few meters per hour.