碩士 / 國立中央大學 / 地球物理研究所 / 99 / The Gaoping submarine canyon, connecting to the Gaoping river, is located offshore southwestern Taiwan on an accretionary wedge. Two major sediment transport processes that deliver Taiwan sediments to abyssal South China Sea are operating along the Gaoping canyon. They are flood-induced hyperpycnal flows and turbidity currents caused by submarine landslides. This study examines sediment cores to infer recent depositional processes along the Gaoping submarine canyon. In addition, I use the sequential submarine cable breakages along the Gaoping canyon during 2009 Morakot typhoon to calculate the flow velocity for the flood-induced hyperpycnal flows.
This study collected 17 gravity cores after the 2009 Morakot typhoon and 9 piston cores after the onshore 2010 Liouguei earthquake. Both events are accompanied by two episodes of gravity flows as revealed by series of submarine cable breakages along the canyon.
There are, at least, 3 episodes of submarine cable breakages along the Gaoping canyon during immediately after the 2009 Morakot typhoon. The first hyperpycnal event (2009/8/9) resulted in three locations of cable breakages in the middle and lower reaches (1200-2702 m). The flow velocity exceeded 11 m/s. Timing for this event correlates well with the peak flood of the Gaoping river. It is therefore interpreted as a hyperpycnal-flow event caused by high sediment concentration. For the second event (2009/8/12), there are 8 locations of cable breakages along the lower reach of the Gaoping submarine canyon and the Manila trench with water depth ranging from 2900 m to 3500 m. The flow velocity exceeded 23 m/s. Timing for this event coincides with lower river run-off. I therefore interpret that this event is a turbidity current caused by, perhaps, submarine landslides. For third event (2009/8/13), there is only one location of cable breakage in the middle reach lying at a water depth of 1600 m.
The onshore Liouguei earthquake induces submarine landslides that evolves into turbidity currents and flows the lower slope of accretionary wedge and the Manila trench as evidenced from. Submarine cable breakages lying in a water depth of 2700-3700 m. The velocity for this turbidity current exceeded 9 m/s.
Analyses on sediment cores reveal that the Gaoping submarine canyon is controlled by three main depositional processes: hyperpycnal flows triggered by extreme onshore floods; turbidity currents caused by submarine landslides; hemipelagic deposition.
Sediment by passing and erosive currents are the characteristic features in the upper and middle reaches of the canyon. By contrast, coarser-grained sediment deposition both in channel thalwegs and overbank areas are characteristic in the lower reach of the canyon due to a sudden decrease on canyon gradient. This study reveals that terrigenous materials are transported to deep sea along canyon by hyperpycnal flows during severe floods. Mineral contents and values of δ13C measured from sediments indicate that most of the sediments along the Gaoping canyon are sourced from the Taiwan mountain belt. Turbidity currents triggered by submarine landslides serve as another major sediment transport agent that deliver sediments accumulated in the Gaoping canyon to the Manila trench.
| Identifer | oai:union.ndltd.org:TW/099NCU05134024 |
| Date | January 2011 |
| Creators | Shih-Lin Tseng, 曾世霖 |
| Contributors | Andrew Tien-Shun Lin, 林殿順 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 140 |
Page generated in 0.0015 seconds