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 more 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 (~50 km). The estimated volume of lava erupted is 18--76¿106 m3 for the extrusion and 100--150¿106 m3 for the intrusion. The total volume is consistent with the volume from modeling of seafloor strain measurements recorded during the event. ¿ 1999 American Geophysical Union