HR: 14:45h
AN: V43F-05    [Abstracts]
TI: Active Volcanic and Hydrothermal Processes at NW Rota-1 Submarine Volcano: Mariana Volcanic Arc
AU: * Embley, R W
EM: robert.w.embley@noaa.gov
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Baker, E T
AF: NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Butterfield, D A
AF: JISAO/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Chadwick, W W
AF: CIMRS/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: de Ronde, C
AF: Institute of Geological & Nuclear Sciences, 30 Gracefield Rd., Lower Hutt, 31-312 New Zealand
AU: Dower, J
AF: Biology Dept and School of Earth & Ocean Sciences, U. Victoria, Victoria, B.C V8W 3N5 Canada
AU: Evans, L
AF: CIMRS/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Hein, J
AF: U. S. Geological Survey, 345 Middlefield Rd., MS 999, Menlo Part, CA 94025-3591 United States
AU: Juniper, K
AF: GEOTOP-UQAM-McGill Research Centre, C.P. 8888, Succursale Centre-Ville, Montreal, QUE CA H3C 3P8 Canada
AU: Lebon, G
AF: JISAO/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Lupton, J E
AF: NOAA/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Merle, S
AF: CIMRS/PMEL, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Metaxas, A
AF: Depart. Oceanography, Dalhousie University, Halifax, N.S B3H 4J1 Canada
AU: Nakamura, K
AF: National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567 Japan
AU: Resing, J E
AF: JISAO/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Roe, K
AF: JISAO/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115-6349 United States
AU: Stern, R
AF: Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688 United States
AU: Tunnicliffe, V
AF: Biology Dept and School of Earth & Ocean Sciences, U. Victoria, Victoria, B.C V8W 3N5 Canada
AB: Dives with the remotely operated vehicle ROPOS in March/April 2004 documented a volcanic eruption at NW Rota-1, a submarine volcano of basaltic composition located at 14\deg 36.0'N, 144\deg 46.5'E lying 65 km northwest of Rota Island in the Commonwealth of the Northern Mariana Islands. The site was chosen as a dive target because of the of the high concentrations of H2S and alunite in the hydrothermal plume overlying its summit in February 2003. The summit of the volcano is composed of curvilinear volcanic ridge oriented NW-SE bounded by NE-SW trending normal faults. Lavas collected on the upper part of the edifice are primitive to moderately fractionated basalts (Mg# = 51-66). The eruptive activity is occurring within a small crater (Brimstone Pit) located on the upper south flank of the volcano at 550 m, about 30 m below the summit. The crater is approximately 15 m wide and at least 20 meters deep. The ROPOS's cameras observed billowing clouds of sulfur-rich fluid rising out of the crater, punctuated by frequent bursts of several minutes duration that entrained glassy volcanic ejecta up to at least 2 cm in diameter. ROPOS recorded a temperature of 38\degC within the plume. The volcanic activity had substantial temporal variability on the scale of minutes. ROPOS was sometimes completely enveloped by the plume while on the rim of the crater, and its surfaces were coated with large sulfur droplets. Black glassy fragments were entrained in the plume up to least 50 m above the crater and deposits of this material were on ledges and tops of outcrops up to several hundred meters from Brimstone Pit. The pit crater fluids have an extremely high content of particulate sulfur and extremely acidic, with pH around 2.0. This strongly implicates magmatic degassing of SO$_{2}$ and disproportionation into elemental S and sulfuric acid. Diffuse venting of clear fluids was also present on the summit of the volcano, with temperatures exceeding 100\degC in volcaniclastic sands adjacent to Brimstone Pit. There was also a distinct layer of turbid water on the flanks of the volcano below 700 m that is almost surely related to the eruptive activity. The layer is probably caused by resuspension of material from frequent slope failure due to episodic deposition of ejecta downslope from Brimstone Pit. The vent macrofauna on the summit of NWRota-1 consists of predominantly of shrimps and crabs with a notable dearth of sessile organisms. The unstable slopes and rain of sulfur and volcanic particulates would discourage colonies of less mobile organisms (e.g., mussels tubeworms) found at other Mariana hydrothermal sites.
DE: 8414 Eruption mechanisms
DE: 8424 Hydrothermal systems (8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting