EVIDENCE FOR VOLCANIC-ERUPTION ON THE SOUTHERN JUAN-DE-FUCA RIDGE BETWEEN 1981 AND 1987

THE formation of new ocean crust at mid-ocean ridges is known to be a discontinuous process in both space and time, but little is known about the frequency and duration of eruptions along an active ridge segment. Here we present evidence, from Sea Beam surveys and underwater photography, for the eruption of lavas along a segment of the Juan de Fuca ridge between 1981 and 1987. Although previous studies have inferred volcanic activity on ridges in areas where recent seismicity or young lava flows have been observed 1-4, none has yet had direct evidence to date such a recent submarine eruption. The temporal coincidence between this eruptive episode and the megaplumes (huge, sudden emissions of hot mineral-laden water) observed over this part of the ridge 5,6 in 1986 and 1987 supports previous suggestions 5-10 that megaplumes are caused by sea-floor spreading events.