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 th e North Gorda Ridge, camera tows were conducted at the site in April and di scovered that a lava flow had erupted onto the seafloor during the earthqua ke swarm. The lava flow is located on axis between 42.665 degrees and 42.68 8 degrees N, just south of the axial high of the ridge segment, near the no rthern extent of T-wave epicenters, and under the site where a hydrothermal event plume was found 2 weeks after the swarm began. Temperature sensors o n the camera sled recorded anomalies up to 0.5 degrees 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 SeaBea m 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 x 10(6) m(3). 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 flo w (not imaged by camera or ROV) may have erupted similar to 8 km to the sou th between 42.605 degrees and 42.615 degrees N, where the second half of th e T-wave swarm was concentrated. However, this possible second eruption sit e remains unconfirmed. (C) 1999 Published by Elsevier Science Ltd. All righ ts reserved.