PMEL Earth-Ocean Interactions Program logo National Oceanic and Atmospheric Administration Pacific Marine Environmental Laboratory Earth-Ocean Interactions Program

The CoAxial "Story"


The CoAxial Segment had a well-documented dike injection and eruption episode in June-July of 1993 which was detected and monitored by the NOAA/Navy real-time T-wave monitoring system. Two "event plumes" were found over the axial valley centered around 46° 30'N where the T-waves had concentrated during the latter part of the episode. This site (which subsequently was known as the Flow site) became the target for dives with the Canadian remotely operated vehicle ROPOS off the NOAA R/V DISCOVERER in mid-July, 1993, during which a fresh, venting lava flow 2.5 km long was discovered, mapped and sampled. The lava flow was erupted on a ridge just north of an older volcano cone on the median volcanic ridge. Extensive venting was also found southward from the cone for about 4 km within a small graben. ROPOS recovered rock samples, some water samples, and took temperature measurements. Subsequent NSF/NOAA Alvin dives in October, 1993 (J. Delaney and R. Embley, Co-Chief Scientists) recovered several high quality vent fluid samples and left prominent markers at the sample sites. A magnetics and gravity survey was also conducted at the Flow site during the October dive series (P. Johnson, M. Tivey, and M. Holmes P.I.s).

In the latter part of the DISCOVERER cruise, ROPOS also discovered large quantities of white floc (thought to be bacterial in origin) in the water column and on the seafloor centered around 46û19ÕN. In September of 1993, a Scripps Institution of Oceanography expedition on R/V Melville conducted Deep-tow sidescan and CTD operations in this area and discovered seafloor temperature anomalies at 46° 18'N. Night time CTDT/chemical surveys off the AII in October of 1993 discovered very intense attenuation and high methane plumes and several zones of diffuse venting associated with high bacterial production along a fissure zone that cut through older pillows and sheet flow lavas between approximately 46° 17'N and 46° 19'N. This area became known as the "Floc" site. The biological system was, at that time, characterized entirely by prodigious bacterial productivity, similar to that observed at in 1991 (Haymon et al., 1993) and at the north Cleft site in the late 1980s. A time-lapse camera and temperature probe was emplaced at one of the sites (R. McDuff, PI), several vent fluid and biological samples were recovered, and markers were left at several of the vent sites.

CTD tow-yos made during the night operations of the October, 1993 cruise discovered plumes centered over a ridge in the southern part of the CoAxial Segment centered around 46䓉'N. This site became known as the "Source" site because of an hypothesized relationship to the original source of the T-waves (although it is located several miles south and east of the center of the original T-wave swarm. During the last dive of the 1993 series, a high-temperature vent system was found at 46° 09'N along the easter axial volcanic ridge (the shoalest point in the segment). The two chimneys visited in 1993 vented almost smokeless fluids that formed almost pure anhydrite edifices.

The 1994 CoAxial dives were a continuation of the exploration of the geological, chemical and biologic manifestations of the CoAxial Event and of the time-series studies begun in 1993. Three dives were conducted at the Floc site, three at the Lava Flow, and two at the Source Vent site.