Dredge samples collected from the submarine part of the east rift zone of Kilauea Volcano consist of glassy, tholeiitic pillow basalts containing vesicles whose volume and size decrease systematically with depth. Basalt dredged from seamounts near the Island of Hawaii is weathered, and the large volume of vesicles indicates that the seamounts have submerged as much as 1,700 m since their lava was extruded. Close chemical similarity between the glassy crust of submarine pillows and subaerial lava of the same rift zone indicates that exchange does not take place between sea water and deep sea basalt at the time of eruption. There is no evidence that spilite forms at the time of eruption.