1998 Eruption of Axial Volcano: Multibeam anomalies and sea-floor observations

Lava flows erupted during the January/February 1998 seismic swarm at Axial Volcano on the Juan de Fuca Ridge have been identified by differencing of pre- and post-event multibeam bathymetric surveys and by seafloor observations. A sheet flow mote than 3 km in length and 500-800 m wide erupted from the uppermost south rift is the site of a robust hydrothermal system. 1998 lavas occur over about 9 km of the upper south rift zone, or about 20% of the along-axis length of the seismicity event (similar to 50 km). The estimated volume of lava erupted is 18-76 x 10(6) m(3) for the extrusion and 100-150 x 10(6) m(3) for the intrusion. The total volume is consistent with the volume from modeling of seafloor strain measurements recorded during the event.