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