OCE-9521435 Hydrothermal vents on the ocean floor were discovered nearly twenty years ago, and this discovery led to a new understanding of the oceans. The rate of flow of water from the vents has never been measured directly, it has only been estimated, but the rate of flow is a fundamental character of these vents. Once the flow rate is known, we will be able to answer major questions about relationship of hydrothermal vents to the chemistry of sea water, and to the heat released from the earth. This project will developed and test a sensor that will measure the velocity of fluid flow from hydrothermal chimneys on the ocean floor.