HR: 1340h
AN: T33B-1354    [Abstracts]
TI: AUV Mapping of Axial Seamount, Juan de Fuca Ridge: The Southern Caldera Floor and Upper South Rift
AU: * Clague, D A
EM: clague@mbari.org
AF: MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Caress, D
EM: caress@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 W
EM: bill.chadwick@noaa.gov
AF: CIMRS, Oregon State University 2115 SE OSU Drive, Newport, OR 97365, United States
AU: Butterfield, D A
EM: david.a.butterfield@noaa.gov
AF: JISAO, University of Washington 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 R
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 200 kHz multibeam and 110 kHz sidescan surveys of the south caldera and upper south rift, conducted at 50 m vehicle altitude, achieved sub-meter resolution bathymetry and sidescan imagery. 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 north caldera and northeastern caldera rim. The southern caldera wall is buried beneath at least 5 voluminous lava flows, including the 1998 flow, each erupted from fissures extending along the southeastern edge of the caldera roughly parallel to the upper south rift zone. The caldera wall here was not as tall as on the southwest, north, and northeast of the caldera, and may have been as low as 35 m tall before it was buried. Active and inactive hydrothermal vents are generally located along the inferred buried caldera wall. Eruptive fissures are characterized by series of depressions aligned along each fissure; no ramparts or other constructional edifices were constructed along them. The aligned depressions suggest that lava drained back down the fissures at the end of the eruptions. The fissure eruptions were large volume and had large effusion rates as seen by their interwoven channels and the extent of the flows. Most of these flows have central channels of lineated sheet flows, bordered by folded and then jumbled sheet flows, surrounded by lobate flows with lava pillars and collapse structures and pillowed flow margins. As an example, the 1998 eruption in and near the caldera issued from 5 en echelon fissures extending at least 3 km. The largest flow lobe extending to the south was mapped along its entire western boundary using JASON II, but the flow extends to the southeast beyond the mapped region. An unusual km-across feature was mapped near the center of the caldera. Appelgate and Embley (1992, Bull. Volc. 54, 447-458) inferred that this was a large tumulus based on partial imaging using sidescan sonars. The feature is clearly formed by inflation beneath a rigid lava crust, but does not appear to be above a tube system nor pressurized by hydrostatic head produced as lava flowed downhill. Instead, this feature appears to be a low-relief dome formed of fluid lava. To produce such a feature atop a vent, the eruption rate must have been very low and the thick crust prevented the flow from advancing. As it domed upward, the thick brittle crust cracked and separated, producing fissures as observed on tumuli.
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