HR: 1340h
AN: B13A-0166    [Abstracts]
TI: Off-Axis Lava Transport at the East Pacific Rise 9-10\deg N: Channelized Lava Flows
AU: * Soule, S A
EM: ssoule@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Fornari, D J
EM: dfornari@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Perfit, M
EM: perfit@geology.ufl.edu
AF: University of Florida, 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Ridley, W I
EM: iridley@usgs.gov
AF: US Geological Survey, Denver Federal Center, Box 25046, MS 973, Denver, CO 80225 United States
AU: Tivey, M
EM: mtivey@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Schouten, H
EM: hschouten@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Ferrini, V L
EM: ferrini@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: Extrusive lava flows compose the upper $\sim$500 m of oceanic crust at mid-ocean ridges (MORs). At fast and superfast spreading MORs, this extrusive layer (i.e. seismic layer 2A) doubles in thickness within 2-4 km from the ridge axis. Geophysical measurements and stochastic modeling suggest that the observed thickening of the extrusive lava layer is the product of bimodal lava deposition, both at and away from the axial summit trough (on- and off-axis); however, the mechanism by which lava is transported off-axis is not well-defined. Using high-resolution bathymetry, sonar backscatter intensity maps, and $>$80,000 seafloor digital images contained within a GIS database, we have mapped lava flow features similar to subaerial lava channels that we consider to be the primary mechanism of off-axis lava transport. Channels are distinguished from the surrounding lavas by their low backscatter intensity (they are floored by smooth featureless lava) and by their depressed topography (a result of draining of the liquid lava after the eruption has ceased). Often, only segments of channels are visible along the path of a channel system. The identified channel segments are 50 m to 1.1 km in length. Channel widths are highly variable along single channel systems ranging from 10 to 50 m, but depths are consistently 2-4 m. Channels initiate up to 500 m from the axial summit trough axial summit trough and, when segments composing a channel system are connected, can extend 1-3 km away from the ridge axis. Geochemical analyses indicate that the channelized flows erupted at the AST and are cogenetic with the lobate lava flows in which they occur. We construct detailed maps of the lava surface morphology across the channels from mosaics of down-looking digital images and high-frequency, near-bottom scanning altimetry collected during submersible dives. These maps reveal characteristic, cross-channel variations in surface morphology including brecciated zones of variable width at the channel margins. We interpret the brecciated zones to form from high shear rates at the channel margins and/or by bending of the surface crust as the channel is drained of lava. Using proven results from numerical and physical modeling of submarine lava flows, we are able constrain velocity and shear rate profiles across the channel surface and interpret whether the brecciated region is formed during or after lava transport. In addition, we are able to constrain flux through the channel (i.e. effusion rate) an elusive and important aspect of submarine eruptions with implications for magma supply rate, ridge resurfacing rates, and oceanic crust construction.
DE: 8429 Lava rheology and morphology
DE: 8450 Planetary volcanism (5480)
DE: 3640 Igneous petrology
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology and bottom photography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting