HR: 1340h
AN: T33B-1355    [Abstracts]
TI: AUV Mapping of Axial Seamount, Juan de Fuca Ridge: The Northern Caldera Floor and Northeast Rim
AU: * Caress, D W
EM: caress@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Clague, D A
EM: clague@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Paduan, J B
EM: paje@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Chadwick, W A
EM: bill.chadwick@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, United States
AU: Butterfield, D
EM: david.a.butterfield@noaa.gov
AF: JISAO, Unversity of Washington, PO Box 357941, Seattle, WA 98105, United States
AU: Thomas, H
EM: hthomas@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Conlin, D
EM: conlin@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Thompson, D
EM: drthom@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AB: During September 2006 and August 2007 NOAA NeMO cruises, we conducted 7 high-resolution near-bottom seafloor mapping surveys of Axial Seamount using the MBARI Mapping AUV D. Allan B. The north caldera floor and northeastern caldera rim were surveyed with 200 kHz multibeam and 110 kHz sidescan from altitudes of 50 and 90 m, respectively, achieving bathymetry and sidescan imagery lateral resolution from < 1 m to 1.5 m. Numerous previous and concurrent submersible or ROV dives provide ground-truth of what the maps depict. A companion poster presents the AUV surveys of the south caldera and south rift zone. Numerous young fissures extend north from the center of the north caldera wall along the north rift zone and northward from the northeastern corner of the caldera. One large north rift fissure cuts the caldera wall, extending 300 m south across the caldera floor and containing the CASM hydrothermal vent site. A few narrow fissures, in line with the north rift, crosscut older pillowed flows near 45°57.6`N. The east rim of the caldera is cut by numerous fissures, which are continuations of the south rift zone. These fissures extend as far north as 45°59.4`N and form a subdued horst-and-graben terrain. Some of these fissures erupted voluminous pillow flows on top of 2 m of volcaniclastic sediment on the northeastern rim. The sediment overlies channelized fluid flows predating caldera formation. The youngest north caldera flow erupted from the CASM fissure, partially covering two other large flows erupted from the same region. The CASM flows have central channels of lineated sheet flows and jumbled sheet flows, flow margins of lobate flows that grade outward to pillowed margins, and only rare collapse structures. Along channel margins in the jumbled sheet flows, crustal fragments have stacked up into lava spires several m tall. One of two large flows erupted near the eastern caldera wall flowed N and the other flowed W until it encountered the western caldera wall, then turned N and finally NE. The distal end of this flow has a peculiar mottled pattern in the bathymetric data; it consists of jumbled sheet flows with small ridges of broken crusts. A 150-m across pillow cone with a 32 m deep central crater is apparently the oldest volcanic feature in the north caldera floor. The southern flank of this cone is truncated by a 070° scarp. Along the northeast caldera wall there is a smooth lava pond with a jumbled sheet flow surface. The pond has a flat bottom (1580 m depth) and is bordered to the east and south by a 4 m high lava highstand (bath-tub ring). Inside the pond, we observe 12 mounds consisting of uptilted slabs of pond crust draped over large pillars. A second small region of flat pond surface, located just SE of the cone, is at the same depth and may have once been contiguous with the eastern pond. Adjacent to the small pond is a segmented ring of spatter levees with channels cut through in all directions.
DE: 8178 Tectonics and magmatism
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 8440 Calderas
SC: Tectonophysics [T]
MN: 2007 Fall Meeting