During August/September 1984, the submersible ALVIN visited a large, active hydrothermal system on the Juan de Fuca Ridge. A time-lapse camera, taking photographs every 42 minutes for six days, was deployed at an active vent to characterize the dynamic nature of this system. This report documents the growth rate of a low temperature (measured at 56¿C) hydrothermal deposit and establishes that this growth is not constant; periods of substantial erosion are superimposed upon the general growth pattern. Quantitative photographic interpretation of the suspended particulate load suggests a strong diurnal component to these fluctuations. Water flow, manifest by the movement of attached worm tubes, also shows strong variations but on a semi-diurnal basis correlated to tidal motions.