HR: 09:30h
AN: OS21E-07    [Abstracts]
TI: Slope Instability and Gas Hydrates in the Hudson Canyon Region, U.S. Atlantic Continental Margin
AU: * Rona, P A
EM: rona@imcs.rutgers.edu
AF: IMCS, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901 United States
AU: Robb, J M
AF: U.S Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Butman, B
AF: U.S Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Scranton, M I
AF: Stony Brook University, Marine Sciences Research Center, Stony Brook, NY 11794 United States
AU: Kingman, K E
AF: IMCS, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901 United States
AU: Tucholke, B E
AF: WHOI, Clark 241, MS 22, Woods Hole, MA 02543 United States
AU: Twichell, D
AF: U.S Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
AB: The continental slope and the upper rise centered on Hudson Canyon offshore New York and New Jersey lie within a major gas-hydrate province. This region exhibits evidence of gravitational mass movements and possible methane expulsion, as inferred from our bathymetric and water-column surveys conducted in 2002 with support from NOAA/OE, and prior data. The bathymetric data cover our study area (200 km by 110 km; 37\deg40'N to 39\deg50'N, 70\deg00'W to 72\deg30'W) from the inner edge of the continental slope (depth 200 m) seaward to the middle rise (c.3500 m). The world's largest hub of submarine telecommunications cables partially passes through this area. Evidence of gravitational mass movements and of probable gas release is extensive. Examples of the former include: (1) blocks of landward-dipping strata up to 2-km wide and 150-m high that lie at the base of the continental slope (water depth 2100-2200 m) seaward of an over-pressured zone beneath the continental slope (639 mbsf in ODP Hole 1073A; water depth 650 m; Dugan and Flemings, 2000); (2) boulders of Eocene chalk that litter the lower slope and upper rise; (3) a semicircular, tabular glide block, about 20 km in diameter, which thickens to about 150 m at its seaward margin; the block is centered at 39\deg23.5'N, 71\deg10.0'W between 2450 and 2600 m depth on the upper rise, about 15 km downslope from a congruent scarp at 2200 m on the lower slope; (4) apparent penecontemporaneous faulting and gliding in strata inclined sub-parallel to the seafloor along the upper rise; 5) apparent clogging of Hudson Canyon with hummocky sediment at a right-angle turn of the axis (depth 3368 m; 38\deg39.6'N, 71\deg01.8'W); 6) changes in stratification from the upper to middle rise; uneven layering beneath the upper rise (seafloor mean inclination 0.75\deg down to 2700 m) is inferred to reflect disturbance by gravitational mass movements; even layering parallel to the seafloor beneath the middle rise (inclination increase seaward from 0.25\deg to 0.76\deg) may reflect less disrupted hemipelagic sedimentation. Evidence of gas release includes: (1) a zone of irregular pits, each up to 500-m in diameter and spaced kilometers apart, that extends along the upper rise (2600-2650 m); (2) a line of eight depressions each 50-70 m in diameter with several meters relief and spaced 100-120 m apart that trends NNW (2150 m; near 39\degN, 71\deg52'W)and that may indicate gas or porewater escape along a local fault; 3) a plume of sediment suspended in fluid that is discharging through the seafloor and rising about 1 m at 2625 m depth on the SW margin of Hudson Canyon (38\deg52.4'N, 71\deg31.0'W) recorded on deep-towed video; and 4) three zones of regional, water-column, methane anomalies, which exceed background values, deeper than 2500-m depth, centered at 1200-m depth, and near 200-m depth. These features indicate past and present dissociation of gas hydrates and/or venting of free gas. They also indicate that coherent gravitational mass movements over low seafloor slopes (< 1\deg) have been facilitated by excess fluid (water and/or gas) pressures. The continental slope and rise in the Hudson Canyon region comprise a natural laboratory in which to study slope instability in a gas hydrate province and to assess the hazards to telecommunications cables. Dugan, B. and P.B. Flemings (2000), Overpressure and fluid flow in the New Jersey continental slope: implications for slope failure and cold seeps, Science, 289, 288-291.
DE: 9325 Atlantic Ocean
DE: 4271 Physical and chemical properties of seawater
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting