NeMO Overview - Ed Baker, Chief Scientist Wecoma/CTD Cruise

The NeMO 2001 Water Column cruise fulfilled its mission of monitoring hydrothermal activity along the Juan de Fuca Ridge, obtaining data and samples from three separate geologic areas. Our principal focus, of course, was Axial Volcano, site of the NeMO Observatory. Our cruise this year was the fifth since the eruption of January 1998 reinvigorated hydrothermal venting along the southeast border of the caldera. The previous four cruises have documented first an enormous expansion of hydrothermal activity coincident with the eruption, followed by a rapid decline as the dike that fed the eruption began to cool. We have also monitored changes in the chemistry of the discharge fluids, changes that may be related to changes in the microbial population within the crust. This year's results indicate that hydrothermal activity here continues to wane. We conducted eight "tow-yo" and 26 vertical CTD casts in and around the caldera, collecting hundreds of water samples in the process. These data will be used to produce maps of the distribution and composition of hydrothermal plumes presently overlaying the summit of Axial Volcano. When combined with previous years' data we will be able to summarize the natural history of venting here since the eruption, and improve our understanding of the effects of seafloor eruptions on the chemistry and biology of the deep sea.

We also contributed to the NeMO Observatory network by deploying four moorings to collect plume data for the next 12 months. While we cannot communicate with these moorings as we can with the primary NeMO mooring, they form a critical part of our three-dimensional monitoring of Axial Volcano.

After our work at Axial, we steamed south to the Cleft segment of the Juan de Fuca Ridge. The largest know eruption on the Juan de Fuca Ridge occurred here in 1986, and we have been monitoring its effects yearly since then. This time-series is the longest of any vent site on the ocean floor. It provides our only opportunity to observe slow changes in hydrothermal activity that may have time scales of 10 or 20 years. Knowing the pace of these long-term changes is necessary to accurately interpret shorter-term changes that are more commonly seen. At Cleft we conducted six tow-yos and eight vertical casts, at sites we have regularly occupied for several years.

Our final site was an unusual one in the Blanco Fracture Zone, which connects the Juan de Fuca Ridge with the Gorda Ridge to the south. Fracture zones do not normally host hydrothermal activity, since they mark where the Earth's tectonic plates slide past one another, not where they separate and allow new magma to well up to the seafloor. Several small "pull-apart" basins along the BFZ, however, are thought to be sites of volcanic activity. We have evidence of a seafloor eruption in the East Blanco Depression in 1994, and have been sampling there since then.

One of the most enjoyable aspects of the NeMO work is the opportunity to share our research with students, educators, and the public. We hope the NeMO website has been an informative and enjoyable experience for everyone who has logged on. Our cruise was aided immeasurably by the enthusiasm and hard work of the three students and high-school teacher who joined us. Peter McAuliffe and Angela Opiola, recent graduates of Carlton College and DePaul University, respectively, and David Farr, a junior at Ballard High School in Seattle, all saw oceanography from the inside and learned the rigors and excitement of field work first hand. Missy Holzer, a science teacher from Chatham HS in New Jersey, pitched in to help with the data collection and spent hours writing her logbook to explain our work to the web world.
All of us in the Vents Program hope you will follow our progress in building the NeMO Observatory in the coming years.

Thanks for logging on, and look for us next year!