Logbook
September 20, 1998
Contents:
Today's Science News
Participant Perspective
Logbook from Teacher at Sea
Question/Answer from shore to sea
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
Not available.
Listing of all Perspectives postings
Not available.
Logbook of all Teacher At Sea postings
September 20, 1998
Question:
How will all the the seismic activity occuring off the Oregon Coast
effect the seismic activity on the land in Nothern Oregon? Thank you
for your response.
Karen Lynch- Portland, OR
Answer:
The seismic activity at
Axial Seamount does in fact relate to land
seimicity in the Pacific Northwest, but only in a long-term sense. The
connection is plate tectonics. The seismicity recorded from Axial
Seamount and other sites along the
Juan de Fuca Ridge record the
formation of new oceanic crust. This new seafloor is slowly (2 cm/year)
carried toward the Oregon/Washingtom coast where it subducts beneath the
continent of North America. This subduction process can cause large
earthquakes beneath the coast, as well as affect faults inland. Also,
the subducted material eventually melts and rises to the land surface as
Cascade Volcanoes!
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
All Questions/Answers from sea
Send Your Question to NeMO
(oar.pmel.vents.webmaster@noaa.gov)
Back to Calendar
|