Report on Jackson Segment (Undersea Features) — 4 April-10 April 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 April-10 April 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Jackson Segment (Undersea Features). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 4 April-10 April 2001. Smithsonian Institution and US Geological Survey.
42.15°N, 127.05°W; summit elev. -3100 m
All times are local (unless otherwise noted)
At about 1800 on 3 April an underwater eruption may have occurred at the Gorda Ridge. Volcanic seismicity in the form of T-waves was detected coming from the Gorda Ridge ~200 m W of the S coast of Oregon. The signals were detected at seismometers maintained by NOAA's Pacific Marine Environmental Laboratory (PMEL). They inferred that the seismic events came from the ridge's Jackson segment at approximately 42.15°N, 127.05°W. This spot lies just S of the North Gorda segment, which was the site of an eruption in February 1996. The 3 April signals appeared analogous to those of the February 1996 event, and were located near the summit of the "narrowgate" on the S side and also showed indications of dike propagation. The seismic activity lacked any large main shock, but instead consisted of rapidly repeating earthquakes and intervals of continuous tremor. The activity continued at a moderate rate through at least 9 April, with nearly 2,500 earthquakes detected since activity began. A response effort is being planned by the combined event response team funded by NSF and NOAA using the ship RV Horizon.
Geologic Background. The Jackson Segment of the Gorda Ridge more than 200 km off the coast of Oregon lies immediately SSW of the North Gorda Ridge, the northermost of five segments forming the Gorda Ridge spreading center. The first recorded activity took place in April 2001, when volcanic seismicity was detected by hydroacoustic monitoring. The seismicity indicated possible dike propagation to the south and was similar to that which was documented at the time of the eruption of a submarine lava flow from the adjacent North Gorda Ridge segment in 1996. The 2001 activity originated from the central axial valley of the Jackson Segment, near the "narrowgate" on the southern part of the segment. Later surveys, however, revealed no evidence for submarine eruptive activity in April 2001.