Continental shelf morphology controlled by bottom currents, mud diapirism, and submarine slumping to the east of the Gaoping Canyon, off SW Taiwan

The Gaoping River-Gaoping Submarine Canyon (GPC) is one of the dispersal river systems in the world. Tens of tons of terrestrial sediments discharge per year at the mouth of the river, where gravity-driven flow can damage the telecommunication cable along the 260-km-long GPC; to the east of the GPC, the continental shelf has been eroded. To understand this geological phenomenon, high-resolution sparker seismic data around the continental shelf as well as parallel and across the GPC were collected. Deep-towed sub-bottom profiler (SBP) data and data from shipboard acoustic Doppler current profiler were also collected. Three major system tracts off southwest Taiwan were identified, based on which the coastline of the last glacial maximum was identified at approximately 138 m below the current sea level. Analysis of the deep-towed SBP profiles suggested sandy sediment overflows through breakages on the east bank of the GPC. A convergence of bottom currents with a speed of up to 1.5 m/s flowing southeastward has eroded the continental shelf intensively, forming the Xiaoliuchiu channel. Although a mud diapir is active to the east of the GPC and forms the Xiaoliuchiu islet, it has been eroded at the Xiaoliuchiu channel. The average erosion rate on the east bank of the GPC was estimated to be approximately 609 cm/ka in the past 8.2 ka; between the GPC and the Xiaoliuchiu islet, the continental shelf is wasted due to severe seabed slumping.