海底峽谷為陸源沈積物向大洋輸出的主要通道。如同陸上峽谷一般，由於峽谷中流體流動或周邊地質環境的改變，可分為侵蝕型及堆積型的峽谷。侵蝕型的峽谷由於流體對峽谷壁的長期沖刷與侵蝕作用，往往會造成海床的不穩定而引發海底崩塌，若峽谷侵蝕作用正巧位在地質環境不穩定的區域如天然氣水合物解離區時，侵蝕作用將會加劇進而誘發大規模的海底崩塌，進而破壞海底電纜或者管線，除了造成生活上的不變之外，更可能引發海嘯而造成生命財產的重大損失。因此，本研究主要目的即是以三年時間規劃使用多重尺度近海床高解析之海洋地球物理的探測方法，針對高屏峽谷流域中至上游，及其周邊區域於颱風或洪水等極端氣候事件前後進行重複性觀測，並進行觀測區域淺層地層，尤其是因濁流或者海底山崩所引發的巨量搬移堆積物（Mass transportation deposit; MTD）的時空變遷情形，以瞭解研究區域海底地形及淺層地層的動態變化。第一年計畫目前已蒐集兩個航次密集式二維測線資料，初步結果發現高屏峽谷上游南北兩岸間的地質環境有明顯差異：南岸遭受泥貫入體上拱作用呈現侵蝕環境，北岸則反幾乎是堆積環境，目前資料正在處理及分析中。但為確實瞭解海底崩塌及濁流的動態行為，需要針對研究區域進行長時間多年期的觀測方可達成本研究最終目的：高屏峽谷上游區域地質災害的時空變化，以瞭解海底峽谷的沉積物搬運與周圍地體構造的關聯性。 ;As a major pathway of the sediment transportation, the submarine canyons sculpture the seafloor then deposit sediments at the deep ocean. The submarine canyons could be divided into two categories: erosive or deposition based on geological environment or fluid flow down to the canyon. The erosive canyons often “attack” the levee which may result in submarine landslides or mass transportations due to slope failure. Once slope failure occurs at geological weakness area such as gas hydrate dissociation zone, giant mass slumping will be triggered. These kinds of mass transportations will further develop turbidity current or hyperpycnal flow, which could damage the submarine fiber optic cables or pipes. The giant mass transportation even triggers devastated tsunami. Therefore, we propose a three year and apply multiple near seafloor high resolution geophysical observation methods such as swath bathymetry, spark type MCS, sub-bottom profiler as well as side scan sonar in mid-to-up stream Gaoping submarine canyon area. The strategy is repeating geophysical surveys before and after devastated typhoon and flooding events during three year project. We have conducted two high resolution geophysical surveys along and across the upstream Kaoping Canyon area since end of August, 2017 during first year project. The preliminary results show that an erosional environment may be controlled by active mud diapirism, an opposite depositional environment is in the north of the canyon. These data are still under processing and analyses. In addition to understand the temporal variation and relationship with tectonic processes not only on mass transportation deposits but also on dynamics of turbidity and hyperpycnal flow, multi-year observation strategy must be applied.
