FY 1994

Introduction to special section on volcanic and hydrothermal processes on the southern Juan de Fuca Ridge

Embley, R.W., R.A. Feely, and J.E. Lupton

J. Geophys. Res., 99(B3), 4735–4740, doi: 10.1029/93JB03217 (1994)

In September 1986, during an investigation of the thermal and chemical properties of the water column overlying the southern Juan de Fuca Ridge (JdFR), a plume of hydrothermal effluent of extraordinary size and heat content was discovered [Baker et al., 1987]. The center of this "megaplume" (and a subsequent one found in 1987) was several hundred meters shallower than the "steady state" hydrothermal plume observed over the ridge and contained the equivalent of about 1 year's discharge from a typical ridge crest vent field [Baker et al., 1989]. A conductivity- temperature-depth (CTD) profile taken 1 month later at the site revealed that the megaplume was no longer present. Modeling of the dynamics of megaplume generation revealed that it was consistent with a sudden expulsion of fluids from a preexisting hydrothermal system, probably from a fissure produced during an episode of seafloor extension [Baker et al., 1989]. Independent evidence for this interpretation was discovered when subsequent surveys of the northern Cleft segment using Sea Beam, side scan sonar and deeply towed camera revealed that a basaltic fissure eruption had occurred in the area between 1983 and 1987 [Chadwick et al., 1991; Embley et al., 1991; Fox et al., 1992]. The discovery of the megaplume focused a broad research effort within the source area on the northern portion of the Cleft segment (Figure 1). This special issue is an outgrowth of a special session at the Fall 1991 AGU Meeting and includes results of several years of interdisciplinary field investigations focused on this area.