HR: 1330h
AN: T32A-0913    [PDF]
TI: New Mapping of Mariana Submarine Volcanoes with Sidescan and Multibeam Sonars
AU: * Embley, R W
EM: robert.w.embley@noaa.gov
AF: NOAA, Pacific Marine Environmental Laboratory, 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Chadwick, W W
AF: CIMRS, Oregon State U., 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Baker, E T
AF: NOAA, Pacific Marine Environmental Laboratory, 7600 Sand Pt. Wy. NE, Seattle, WA 98115 United States
AU: Johnson, P D
AF: SOEST, U. Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Merle, S G
AF: CIMRS, Oregon State U., 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AU: Ristau, S
AF: NOAA, Pacific Marine Environmental Laboratory, 2115 SE O.S.U. Dr., Newport, OR 97365 United States
AB: An expedition in February/March 2003 on the R/V Thomas G. Thompson mapped more than 18,000 km$^{2}$ with the towed MR1 sidescan sonar and almost 28,000 km$^{2}$ with an EM300 hull-mounted multibeam system along the Mariana volcanic arc. The expedition was funded by NOAA's Office of Ocean Exploration (more on the expedition can be found at: http://oceanexplorer.noaa.gov/explorations/03fire/welcome.html). The MR1 sidescan surveys began at the northern end of a 2001 R/V Melville MR1 survey at 16§ N and extended to Nikko Volcano at 23\deg 05'N. A portion of the southern back-arc spreading center and the arc volcanoes south of 16\deg N were mapped using the EM300 system. Of 43 submarine arc volcanoes surveyed that have basal diameters of 10 km or greater, 17 have summit calderas or craters. Of these, however, only 5 have diameters more than 2 km. In an accompanying survey of hydrothermal activity along the arc, CTD casts and/or tows were conducted over more than 50 individual volcanoes. The 11 volcanoes with active hydrothermal systems found in the course of these surveys appear to be about equally divided between those with and without summit calderas or craters (for additional information, see Baker et al., Resing et al., and Lupton et al., this session). The flanks of the submarine volcanoes and islands of the central and northern Mariana Arc consist largely of volcaniclastic flows. Most of the larger edifices have high-backscatter spoke-like patterns that probably represent coarser and/or younger flows from the summits. Higher relief high-backscatter areas, also commonly exhibiting a radial pattern, are found on many of the volcanoes' flanks. These are probably lava flows erupted along radial fissures. The Mariana Arc volcanoes are shedding large volumes of volcaniclastic material westward into the back-arc basin through a series of deep-sea channels oriented transverse to the arc that are in many places fed by flows from several volcanoes. On many of the volcaniclastic aprons of the islands and larger submarine volcanoes, sediment waves with wavelengths of up to 1.0 km and amplitudes up to 50 m commonly occur. Their crests are almost always oriented parallel to regional contours, indicating a formation mechanism related to down slope flow. In some places clear transitions occur between mass flows on the volcanoes' steeper flanks and the sediment waves on the gentler slopes of the apron. A preliminary interpretation is the sediment waves form during the transition from channelized to unconstrained flows. Sediment waves of similar scale are commonly observed on the levees of deep-sea channels and on deep-sea fans. The location and shape of the arc volcanoes are often controlled or influenced by tectonic control. Within the southern part of the Central Island Province, from about 15\deg 50' N to 18\deg 00' N, volcanoes often line up and/or are elongated in an E-W or an E-NE direction. There are several cross-chains of volcanoes in this region that penetrate 10's of kms into the back-arc basin. Along the northern part of the arc (the Northern Seamount Province), where the convergence direction is roughly parallel to the arc front, the structure is more complex. Several active volcanoes occur at the intersection of two or more structural lineaments northwest of Farallon de Pajaros Island. There are several volcanoes in the northern area that are narrow ridges striking in a S-SW trend 9 (arc-orthogonal).
DE: 3045 Seafloor morphology and bottom photography
DE: 8499 General or miscellaneous
SC: Tectonophysics [T]
MN: 2003 Fall Meeting