HR: 0800h
AN: V51C-1497 INVITED     [Abstracts]
TI: Tempest in Vailulu'u Crater
AU: * Hart, S R
EM: shart@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road., Woods Hole, MA 02543 United States
AU: Staudigel, H
V51C-1497 AF: Scripps Institution of Oceanography, Univ. of Calif., San Diego, LaJolla, CA 92093 United States
AU: Koppers, A
V51C-1497 AF: Scripps Institution of Oceanography, Univ. of Calif., San Diego, LaJolla, CA 92093 United States
AU: Young, C
V51C-1497 AF: Oregon Institute of Marine Biology, P.O. Box 5389 University of Oregon, Charleston, OR 97420 United States
AU: Baker, E
V51C-1497 AF: NOAA Pacific Marine Environmental Lab, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AB: The summit crater of the Samoan submarine volcano, Vailulu'u, has been actively erupting since 2001. Based on water chemistry, CTD and temperature logger data from 2000 and 2001, we formulated a model for the hydrothermal system in the crater involving a tidally-modulated "breathing" (Staudigel et al., 2004). During low stands of internal waves (exterior to the crater), the crater exhales warm buoyant hydrothermal water that forms a "halo" around the crater rich in Mn, 3He, and particulates. During "high tides", cold dense external water is inhaled into the crater through the three breaches, and cascades to the crater floor. In April 2005, we used the HURL PISCES V submersible to deploy various temperature and particulate loggers and current meters in and around the crater; these were retrieved by Pisces V in July 2005. In addition, continuous CTD profiling was carried out over 12 hour tidal cycles at one location inside, and one outside, the crater. The accumulated data set fully reinforces our "breathing" model. An ADCP, deployed for 93 days in the NW breach at 752m, showed dominant easterly inflow currents and westerly outflow currents, with maximum velocities of approximately 25 cm/s. The flows were coherent for distances up to 50-60m above the ADCP; the mean inflow velocity and azimuth (20-40 m interval above the ADCP) was 7 cm/s due east; the mean outflow velocity and azimuth was 5 cm/s at 260 degrees. Mean inflows were consistently colder than outflows (5.00 C vs 5.20 C); the maximum observed range in temperature was 1.1 C, correlated with peak flow velocities. The coldest inflows would require very large regional internal wave amplitudes, up to 50-100 meters. A 2-D acoustic current meter was deployed on top of the west crater rim summit (582m) for 90 days, and in the S breach (697m) for 4 days. The summit flows are presumed to represent the regional scale currents; these were largely from the SW quadrant, with typical velocities of 8-15 cm/s, and peaks to 25 cm/s. The S breach flows had a clear semi-diurnal tidal modulation, with strong NE quadrant inflows at high velocity (15-30 cm/s), separated by short outflow spikes of 1-2 hour duration at much lower velocity (greater than10 cm/s). The outflow water was typically warmer by 0.1-0.2 C; the maximum temperature range was 0.6 C, about half of that observed at the NW breach. A 12-hour continuous profiling CTD-LBSS station was serendipitously sited on top of a large diffuse-venting hydrothermal field, in the crater moat just north of the new volcanic cone. The water column here was incredibly dynamic, with a 5-10m bottom boundary layer, 1 C above ambient, forming by diffuse flow from the basalt substrate in a matter of minutes; this layer would destabilize, detach, and rise with velocities of ~ 1 cm/sec. This buoyant water was both warmer and less saline than either the ambient crater water, or the cold outside water which occasionally cascaded onto this site from the nearby NW breach; it was also laden with particulates, with LBSS readings up to 1.7 NTU. Water chemistry and He isotope analyses are in progress.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3075 Submarine tectonics and volcanism
DE: 4562 Topographic/bathymetric interactions
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005