In situ observations of the onset of hydrothermal discharge during the 1998 submarine eruption of Axial Volcano, Juan de Fuca Ridge

A volcanic eruption at the summit of Axial Volcano on January 25, 1998, ins tantaneously created extensive and vigorous hydrothermal discharge. Mooring s 2 km apart along the eruption fissure recorded temperature increases of s imilar to 0.6 degrees C up to 115 m above bottom within hours of initial se ismic activity. Water temperatures at the mooring sites remained high for a bout 5 days, then declined steadily over the next 2 weeks. A response cruis e 18 days after the eruption found hydrothermal temperature anomalies of si milar to 0.1 degrees C over the eruption site, and a more intense and much thicker plume 20 km downstream of the eruption. We estimate the steady-stat e heat flux required to produce this distal plume, evidence of discharge co nditions perhaps 1-13 days after the eruption, as 60-230 GW. The Axial erup tion thus produced the largest vent field heat flux yet measured, but these high levels lasted less than 3 weeks.