The 1996 Gorda Ridge eruption: geologic mapping, sidescan sonar, and SeaBeam comparison results

As part of a response effort following the February 1996 T-wave swarm on the North Gorda Ridge, camera tows were conducted at the site in April and discovered that a lava flow had erupted onto the seafloor during the earthquake swarm. The lava flow is located on axis between 42.665° and 42.688°N, just south of the axial high of the ridge segment, near the northern extent of T-wave epicenters, and under the site where a hydrothermal event plume was found 2 weeks after the swarm began. Temperature sensors on the camera sled recorded anomalies up to 0.5°C over and near the new flow, showing that it was still actively cooling. Data from camera tows, remotely operated vehicle (ROV) dives, sidescan sonar imagery, and SeaBeam resurveys show that the new flow is 2.6 km long, 400 m wide, and up to 75 m thick, with a volume of 18×106 m3. We interpret that this flow was erupted during the first half of the T-wave swarm. A combination of T-wave, plume, sidescan, and SeaBeam evidence also suggests that another lava flow (not imaged by camera or ROV) may have erupted ∼8 km to the south between 42.605° and 42.615°N, where the second half of the T-wave swarm was concentrated. However, this possible second eruption site remains unconfirmed.