FY 1987

Cataclysmic hydrothermal venting on the Juan de Fuca Ridge

Baker, E.T., G.J. Massoth, and R.A. Feely

Nature, 329(6135), 149–151 (1987)

Serial observations of individual submarine hydrothermal vents and the mapping of dilute hydrothermal plumes extending far downcurrent from vent fields indicate a stability of vent field fluid composition and mass flux on at least decadal time scales. The inherent episodicity of ridge-crest tectonic activity, however, suggests that discontinuous emissions of hydrothermal fluids also occurs. In support of this hypothesis we report here the discovery of a 700-m-thick, 20-km-diameter eddy-like "megaplume" created by a brief but massive release of high-temperature hydrothermal fluids near 44°49N, 130°140W on the Juan de Fuca Ridge. The megaplume had a mean temperature anomaly of 0.12°C and overlay compositionally distinct plumes emanating from an apparently steady-state vent field at the same location. The megaplume was formed in a few days yet equalled the annual output of between 200 and 2,000 high-temperature chimneys.