HR: 1340h
AN: OS33A-0989    [Abstracts]
TI: Hyperpycnal transport of terrigenous materials from river to ocean: An example of the 2003 Hokkaido Hidaka Flood
AU: * Ikehara, K
EM: k-ikehara@aist.go.jp
AF: Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Katayama, H
EM: katayama-h@aist.go.jp
AF: Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Sagayama, T
EM: tsaga@gsh.pref.hokkaido.jp
AF: Geological Survey of Hokkaido, Chikuko 3-1, Otaru, 047-0008, Japan
AU: Suga, K
EM: suga@gsh.pref.hokkaido.jp
AF: Geological Survey of Hokkaido, Chikuko 3-1, Otaru, 047-0008, Japan
AU: Irino, T
EM: irino@ees.hokudai.ac.jp
AF: Hokkaido University, N10-W5 Kitaku, Sapporo, 060-0810, Japan
AU: Omura, A
EM: a-omura@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo, 164- 8639, Japan
AB: Flood event is an event to supply large amount of terrigenous materials to marine environments. Thus, it is very important process for sea bottom environments, material cycles in the ocean, and strata formation. Mode of dispersion and deposition of flood sediments and its controlling factor is not fully clarified yet. In August 2003, hard rain by the typhoon 200310 occurred in Hidaka area, Pacific coast of Hokkaido, northern Japan. Many land slides occurred by this hard rain, and large amount of terrigenous sand and mud supplied to ocean through rivers. Previous study on this flood indicated that the importance of the inner shelf morphology on mode of flood material transport, especially on maintenance the energy (density) of the flow from the river. Collected sediment cores from mid shelf have some characteristics of hyperpycnal flow deposits. Typical sediment sequence changes from well-sorted very fine sand to brown silt. The uppermost silt has a lot of plant debris indicating after- flood deposition. Further long-distance transport by the hyperpycnal flow was recorded in the sediments of the slope. The large amount of terrigenous mud supply changed the sea bottom condition just after the flood. Most of the flood mud deposited on the inner shelf was removed by waves and currents after the flood. However, thickly deposited flood mud in the inner shelf depression still keeps its thickness due to relatively weak wave and current influence in the depression. Therefore, flood influence disappeared in the most of inner shelf, but still remains at the selected part of the inner shelf.
DE: 1821 Floods
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting