Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

H (Human Geosciences) » H-CG Complex & General

[H-CG23] Turbidity current: from triggers for the generation to the depositional and morphological processes

Mon. May 21, 2018 1:45 PM - 3:15 PM 102 (1F International Conference Hall, Makuhari Messe)

convener:Miwa Yokokawa(Osaka Institute of Technology), Norihiro Izumi(Faculty of Engineering, Hokkaido University), Takeshi Nakajima(産業技術総合研究所地圏資源環境研究部門, 共同), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Chairperson:Yokokawa Miwa, Izumi Norihiro(Hokkaido University)

1:45 PM - 2:00 PM

[HCG23-01] Direct Measurements of the Evolution and Impact of Sediment Density Flows as they Pass Through Monterey Submarine Canyon, Offshore California

★Invited Papers

*Charles K Paull1, Peter J. Talling3,2, Katherine L. Maier4,1, Daniel Parsons5, Jingping Xu6,7, David W. Caress1, Roberto Gwiazda1, Eve Lundsten1, Krystle Anderson1, Jim Barry1, Mark Chaffey1, Tom O'Reilly1, Kurt Rosenberger4, Jenny Gales3,8, Brian Kieft1, Mary McGann4, Steve Simmons5, Mike McCann1, Esther J. Sumner3, Coordinated Canyon Experiment Team (1.Monterey Bay Aquarium Research Institute, 2.Univ. of Durham, 3.National Oceanographic Center, 4.U.S. Geological Survey, 5.Hull Univ., 6.Ocean Univ. of China, 7.Southern Univ. of Sci. and Tech., 8.Univ. of Plymouth)

Keywords:Turbidity Flows, Submarine Canyons, Seafloor Mapping

Sediment density flows flushing through submarine canyons carry globally significant amounts of material into the deep sea to form many of the largest sediment accumulations on Earth. Despite their global significance, these flows remain poorly understood because they have rarely been directly measured. Here we provide an initial overview of the recently completed Coordinated Canyon Experiment (CCE), which was undertaken specifically to provide detailed measurements of sediment density flows and their impact on seafloor morphology and sedimentology. No previous study has deployed as extensive an array of monitoring sensors along a turbidity current pathway. During the 18 months of the CCE, at least 15 sediment density flows were recorded within the axis of Monterey Canyon. Because no external triggers (i.e., earthquakes or floods) correlate with these flows, they must have originated as failures in the canyon floor or canyon flanks. Three flows ignited and ran out for > 50 km from water depths of <200 to >1,860 m, reaching velocities up to 8.1 m/s. The rest of the flows died out within the array. During these events, large objects on or in the canyon floor were displaced substantial distances downslope, including a 7.1 km downslope movement of an entire mooring; a 4.6 km displacement of an 860 kg instrument frame followed by repeated down canyon displacements of this same frame after it was entombed in sediment; and multiple depth changes of man-made boulders containing acceleration and pressure sensors. During this same time interval the canyon floor was mapped six times with autonomous underwater vehicles covering the canyon thalweg at the upper and lower end of the instrument array (200-540 and 1350- 1880 m water depths). The repeated mapping surveys reveal that flows caused +3 to –3 m bathymetric changes within a continuous clearly defined ~200 m wide swath running along the canyon axis in <200 to >540 m water depth. This study shows that sediment density flows caused massive remolding of thick sections of the canyon floor in <540 m water depth as a consequence of displacement or fluidization of entire slabs of the seabed during these events.