Contrasting Development of the Latest Quaternary Slope Failures and Mass-Transport Deposits in the Ulleung Basin, East Sea (Japan Sea)

摘要

In order to understand how the variations in shelf morphology and sediment supply to the shelf within a basin can change the occurrence styles of slope failures and mass-transport deposits (MTDs), this chapter details dimensions and morphology of the latest Quaternary slope failures and MTDs on the western and southern margins of the Ulleung Basin. On the western margin, the slides and slumps have relatively small dimensions with a few small, scoop-shaped scars and gullies deeper than 700 m water depth. The downslope mass-flow deposits occur as small, solitary lobes restricted at the base-of-slope. On the western margin, the small sediment input to the shelf and the prominent Hupo Bank and Hupo Trough blocking sediment delivery to the slope probably caused relatively low accumulation of muddy sediments in the slope, most likely resulting in the small dimensions of slope failures, and the restricted occurrence of small MTDs at the base-of-slope. In contrast, the southern margin is characterized by large dimensions of gullied scars with huge slides and slumps deeper than 250 m water depth. These catastrophic failures evolved into extensive mass flows, which travelled downslope for several tens of kilometers. On the southern margin, the flat, broad shelf and the high sediment supply to the shelf during the last glacial period probably caused relatively high accumulation of mixed muddy and sandy sediments in the upper slope. These conditions could have promoted large-scale slope failures along the entire upper slope, forming the extensive occurrence of MTDs in the middle to lower slopes. This study provides an example that the variations in shelf morphology and sediment supply to the shelf within a basin can affect the styles of slope failures and MTDs by controlling sediment input and sediment types to the slope.