Jackson Segment of Gorda Ridge NE Pacific Ocean; Submarine

By Gari Mayberry - USGS Volcanic Activity Report

Scientists from NOAA used the T-phase Monitoring System to search for megaplumes from a possible eruption of the Jackson Segment of the Gorda Ridge that began on 3 April. They did not find evidence of a plume after collecting 25 vertical hydrographic casts during 11-16 April. Two bottom camera tows were also collected, but the film had not been developed at the time of this report. By 11 April seismic activity was at very low levels, possibly below the detection threshold of the T-phase Monitoring System.

Background. The Jackson segment of the Gorda Ridge lies immediately SSW of the North Gorda segment, about 200 km W of the southern Oregon coast. A submarine lava flow was erupted in February-March 1996, near the center of the nearby North Gorda Ridge segment. The eruption was initially detected through acoustic T-waves from a seismic swarm and the emission of large thermal plumes. In April submarine cameras revealed new lava flows about 100-200 m wide along a fissure that was at least 3.5 km long. A seismic swarm of uncertain origin also occurred at this location in January 1998.

Source: National Oceanic and Atmospheric Administration http://www.pmel.noaa.gov/vents/acoustics/seismicity/nepac/gordaridge01.html