Figure 1: Results of preliminary simulation models for the TAG mound showing the temperature distribution and velocity field. The hydrothermal vent is located adjacent to the boundary on the left. The temperature contour interval is 50?C. Black velocity vectors outside of the vent are scaled to show relative magnitudes. The grey arrows are superimposed to illustrate the general circulation pattern where flow velocities are relatively low. Boundary conditions are shown in (a) and specified fluid mass flux at the vent is 2.49 kg/s; permeabilities of 10-8 m2, 10-13 m2, and 10-12 m2 reflect the vent at x=0-0.2m, the sulfide mound from x=0.2-75m, and basalt from x=75-150m. (a) Base case, (b) a low-permeability zone within the vent simulates a constriction, (c) and (d) fractures and a constriction are simulated.