9633531 Lowell Title: Numerical modeling of two-phase seawater flow in oceanic hydrothermal systems using parallel computers Hydrothermal circulation within the ocean crust controls both heat and mass transfer between the crust and the ocean at mid-ocean ridges. We can not view this process in action because of its inaccessibility but computer simulations can help us understand the reactions that occur. These reactions are complex because they involve the boiling of seawater under high pressure, which can be an unstable process. The PI has developed a computer program that simulates the circulation of fresh water through a hydrothermal system on land and has applied it to Lassen Peak. New measurements of the temperature and pressure of boiling of seawater, and the formation of salt-free vapor and salt-laden brine will be incorporated into this computer model to determine the effect of circulating seawater in a sub-seafloor hydrothermal system.