Simultaneous velocity, temperature, and conductivity data were taken in the convective flow emanating from a hydrothermal vent field located at 10¿56'N, 103¿ 41'W on the East Pacific Rise. The horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution. Such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information. The results of these independent calculations are in close agreement, yielding a total heat flow from this vent site of 3.7¿0.8 MW and a maximum height of 150¿10 m. The nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values. ¿ American Geophysical Union 1987