Leased SSS
|
|
from Western Region Marine and Coastal Surveys Bulletin, July 26,
|
1996...
|
|
Good eating (and results) on the Disco
|
Jane reid sends news from
|
National Oceanic and Atmospheric Administration (NOAA)'s
|
|
research vessel Discoverer (aka Disco), where
|
she, Kim Klitgord (co-chief scientist), and about half a dozen other USGS'ers
|
are cooperating with NOAA in a three-week cruise off the pacific northwest. They
|
are collecting sidescan-sonar and seismic-reflection data in three areas: (1)
|
the coaxial segment of the Juan de Fuca Ridge, where a volcanic eruption
|
occurred in 1993; (2) the northern part of the Gorda Ridge, where a volcanic
|
eruption occurred in april of this year; and (3) Escanaba Trough (southern Gorda
|
Ridge), where hydrothermal vents and a thick blanket of sediment have produced
|
large sulfide deposits analogous to deposits on land.. here is the report Jane
|
sent last week:
|
|
"After some initial problems (non-sinking transponders, sticky winch, and overly
|
hot sidescan system) we are now getting great sidescan and sub-bottom profiles
|
over NOAA's floc area of the coaxial segment of the Juan de Fuca Ridge. The
|
transponder net is well calibrated and the winch is working to fly the towfish
|
at altitudes of about 160 meters above the bottom. The data looks
|
wonderful: fault scarps and fissures and lava structures from recent flows.
|
sidescan images are coming in clear and sharp. Acoustic navigation is
|
intermittent, but Stuart Sides and Miguel Velasco from Flagstaff have kept up
|
with the processing and we expect to have a completed mosaic in the next week or
|
so. After a couple of short deployments and recoveries on the southern part of
|
the Juan de Fuca, it's off to Escanaba Trough for 8 days of side-scan work
|
and seismic lines. The weather has been swell, though we expect it to get
|
sweller (a low is headed our way). The food is excellent. expect some waddling
|
when we return. What we all need are fewer Haagen Daz bars and more Altoids. "
|
for more information about vents in the northeast Pacific (and links to pages
|
about other neat stuff) check out this NOAA page on the world wide web:
|
http://www.pmel.noaa.gov/vents/
|
|
from Western Region Marine and Coastal Surveys Bulletin, August 2,
|
1996...
|
|
More news from the Discoverer
|
The Escanaba part of the survey is collecting great data right now. We have two
|
excellent NW and two NE trending profiles across the mounds region and are about
|
to start the third. Great records on the sidescan, 4.5khz, and airgun systems.
|
the quality is definitely above expectations. Poor fish nav but good ship nav.
|
25-30 knot winds have delayed us a bit due to difficulty holding courses going
|
with the wind, so we have had to make some adjustments to acquire the desired
|
data. Still the prospects for 100% data of the trough, but unless there are
|
major problems we will have not trouble acquiring all of the primary data in the
|
mounds vicinity. Seismic data indicate that we may be able to develop a relative
|
fault age distribution. Rob Zierenberg is thrilled with sidescan images over the
|
mounds with 1000m swaths at 100m above seafloor. Sulfide mound zones are clearly
|
visible. NW trending faults coming into the mounds are "very" linear. could not
|
ask for better images. Very easy to correlate faults and other structures in
|
the airgun data with features on the deep towed sidescan and 4.5khz data.
|
sidescan processing is nearly complete for the NOAA Juan de Fuca co-axial region
|
study and Stuart and Miguel are already working on the Escanaba data. Larry,
|
Mike, and Tom have a superb seismic reflection profile record coming in. Initial
|
processing of seismic reflection data is already underway on Tommy's Silicon
|
Graphics machine, for both airgun and 4.5khz data sets. Swath bathymetric
|
processing for escanaba is about to start but should be easy by comparison with
|
the Juan de Fuca data set. Operations are smooth and the whole team is putting
|
in a great effort. The Williamson team is providing great support.:Kim
|
|
Discoverer's good voyage
|
The Disco is coming into port today, ending the last oceanographic cruise of her
|
30-year career. If all goes as predicted, she "will be escorted in by a fire
|
boat, spraying water as we approach the locks into lake union. We're stopping in
|
Everett to pick up 80 or 100 crew dependents so they can transit the rest of the
|
way in. We should arrive at the dock on Lake Union about 1:30 p.m. on Friday.
|
whee!" Jane Reid
|
|
Here's a recap on the cruise from Kim Klitgord.
|
The NOAA-USGS cruise on the NOAA's Discoverer, with Robert Embley (NOAA) and Kim
|
Klitgord (USGS) as co-chief scientists, has successfully completed its sidescan
|
sonar studies of the co-axial segment of the Juan de Fuca Ridge (NOAA vents
|
program) and the Escanaba Trough on the southern Gorda Ridge. The AMS-60
|
sidescan sonar system and 4.5 khz sub-bottom profiler system leased and operated
|
by Williamson and associates were used for both surveys. At Escanaba Trough,
|
nearly 350 km of near-bottom sidescan sonar and 4.5 khz sub-bottom penetration
|
data and surface towed airgun seismic reflection data were acquired on a grid of
|
18 lines over the Nesca hydrothermal system within the axial valley of Escanaba
|
Trough. A tight grid of 1 to 2 km spacing swaths in both the NNW and NE
|
directions have provided two complete sidescan mosaics with different image
|
angles for interpreting the surficial geologic character of the 18 km x 25 km
|
region centered on the hydrothermal mounds that are the drill target for the
|
ODP leg 169 that starts later this month with Rob Zierenberg (USGS) as co-
|
chief scientist. Stuart Sides and Miguel Velasco (Flagstaff) have already
|
completed the sidescan sonar processing and Rob is hopping from the Discoverer
|
to the Joides Resolution with a set of fantastic mosaics. The 4.5 khz seismic
|
system routinely imaged over 50 meters below the seafloor and provided a superb
|
stratigraphic record of the interlinked volcanism, deformation and turbidite
|
deposition within Escanaba Trough. "z" and Stephahie Ross have been constantly
|
identifying features on these records that they have found on previous dives,
|
camera runs, and sampling sorties. Stephanie, Kaye Kinoshita and Jane Reid
|
(USGS), Bill Chadwick and Julia Getsiv (NOAA), and Jim Fowler (Arizona State)
|
have kept us tightly navigated, ruled the watches and made sure that all we
|
found would not be lost. The 160 cu.in. single channel airgun data provided an
|
excellent image of the entire sediment column and basement structures for the
|
entire area, at times exceeding 1000 m of penetration. Larry Kooker, Mike Boyle,
|
Tom O'Brien and Hal Williams were jumping, keeping the airgun and winch systems
|
fine tuned. Se Won Chang and Hun Soo Choi have become the moguls of
|
swath-bathymetry mapping, keeping Tommy O's Silicon Graphics workstation
|
filled with bits and bytes, occasionally bringing it to its knees. The Escanaba
|
Trough survey revealed a narrow 4-km wide zone of neotectonic activity with the
|
most active faulting and volcanic activity. The recent basaltic flows provided
|
bright sidescan targets enabling us to readily map their areal extent and to
|
identify their likely eruption source: a fissured volcanic hill 2 km east of the
|
hydrothermal central hill of Nesca. The hydrothermal fields on the central hill
|
and southwest hill were clearly identifiable. Growth faults in the 4.5 khz data
|
provide a fine data base for establishing the faulting history within the
|
neotectonic zone to complement the volcanic history.
|