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Logbook
September 20, 1998

Contents:

Chief Scientist Final Report

It's been a few days since we're back on dry land, but I'm still "unwinding" from the very intense and exciting experience of the NeMO98 expedition. The last few days of the cruise was rather stressful because of the very marginal weather conditions. ROPOS could not dive for about 36 hours because of a large swell and high winds, and did not return to the water until about 12 hours from the deadline for beginning our voyage back to Victoria, British Columbia to end the expedition.

But what a dive (Dive 480) it was! We were able to return the refurbished extensometer instruments (photo right: extensometer being pulled from elevator for redeployment) to the seafloor at high points where they could "talk" to one another over the next year. The elevator which carried the instruments to the seafloor was recovered and the RON BROWN then towed the ROPOS down to a vent site called CASM at the northernmost part of the caldera. This site is at the interesection of the north rift zone of Axial with the northern wall of the caldera (SEE MAP). Hydrothermal systems tend to form at places where there are intersections of faults or other structures such as the volcanic rift zones because the rock is more fractured and forms pathways for the fluids. The CASM site was first discovered in 1983 by a group of Canadian (several of whom were participants in the NeMO98 cruise) and U.S. Scientists using the Canadian PISCES IV submersible (now decommissioned) and had not been visited by a submersible or ROV for about a decade. CASM is an acronym for "Canadian American Seamount" (Expedition). The site had changed considerably since the 1980s. One spectacular vent was found lying on a crack in the wall of the fissure just south of its intersection with the caldera wall. This site was unique in that it had a dense colony of the "palm" worms gracefully waving in the currents (photo left: field of palm worms at CASM site). These polychaete worms are usually solitary or in small groups; and its not clear why they would form such a dense colony at this site. Another surprise was the presence of a new high temperature chimney within the large fissure. Chimneys had been seen just outside the fissure, but these had ceased venting high temperature fluids. The new chimney had flow coming from small spires (photo right: spire with tube worms) and intense lower temperature venting around its base. With some difficulty, a high temperature probe was placed in one of the vent orifices and left for the year. Two biologic samples, several scans with the SUAVE, and sulfide sample was taken here. The vent also was emitting what appeared to be bubbles similar to those reported on earlier from the Mushroom vent at ASHES (photo below left) Samples of this fluid taken with the gas sampler should shed some light on the origin and composition of these bubbles.

During the last week of the expedition (Dives 477 and 478), we also were able to complete our goals on the new eruption site. A time-lapse camera (experiment of Verena Tunnicliffe) was placed next to the Marker 33 site which will take pictures at 30 hour intervals over the next year. The camera in conjunction with a long-term Osmosampler (photo below right: Osmosampler at marker 33) and temperature probe, will record the evolution of the chemical and biologic systems associated with the eruption-related hydrothermal system. An attempt at freeing the Rumbleometer from the grip of the lava flow was, unfortunately, unsuccessful (photo below left). Perhaps a more elaborate recovery effort using the power of the surface vessel may be attempted next year.

We also saw the first definitive site where tubeworms had been contacted and fried by the new lava (photo below left) on the eastern contact of the lava flow. Several dead clam shells near the contact suggest that it may have gotten too hot for them also.

NeMO 98 was an outstanding scientific success. On the last day of the voyage, we all gathered together to discuss the results. A feeling that everyone had was that the scientific success of the expedition was primarily because of interaction between the geologists, chemists, and biologists made possible because of the ability of the ROV to bring us all to the seafloor at the same time.

Our success was due not only to the extensive preparation by the scientific party, but to many others both at sea and on land who worked to ensure that the platform was prepared and run efficiently. This includes the seagoing staff of the RON BROWN, the engineers on shore who made sure the ship systems were prepared for the ROPOS, our funding sponsors ( VENTS Program, Sea Grant, the West Coast National Undersea Research Center, and the Canadian National Sciences and Engineering Research Council). The preparation and maintainence of this web page at sea was done through the hard work of Susan Merle and Gene Williamson and on shore by Andra Bobbitt. Mike Goodrich and Vicki Osis at the Hatfield Marine Science Center worked to ensure that the information was disseminated to the public and to the educational community at large. Gene and Mike were both volunteers, so a special thanks to them for their efforts.

We plan to continue this site with updates on the latest research results and plans for the next field season. We hope that's its been as much of a learning experience for all of you out there as it has been for us!

Sincerely,
Bob Embley
Chief Scientist, the NeMO98 Expedition

Listing of all Science News postings

Listing of all Perspectives postings

Logbook of all Teacher At Sea postings

September 20, 1998

Question:

Karen Lynch- Portland, OR

Answer:

Does a seismic event at Axial lead directly to land seismicity? Probably not. The seafloor plates are not perfectly rigid and therefore it is only the long-term accumulation of strain through time that is eventually transferred to the continent. The time scales and other aspects of this process are not well understood and it is hoped that continued study of the ridges will shed more light on this question.

Christopher G. Fox

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