Detailed Bathymetry and Submarine Terraces in the Coastal Area of the Dokdo Volcano in the Ulleung Basin, the East Sea (Sea of Japan)

Abstract

In the northeastern part of the Ulleung Back-Arc Basin, the East Sea, the Dokdo volcano anomalously emerges, rising abruptly from the sea floor (similar to 2,100 m below sea level). It is lying as a cluster of emerged small islets surmounting a larger submerged volcanic edifice. In order to investigate the detailed bathymetry and morphologic characteristics around the volcano's underwater guyot type summit, we carried out multi-beam surveys from 2006 to 2011 and analyzed the data. From the near islets to similar to 30 m depth, the flank slopes are very steep and irregular, overlain by sunken rocks, indicating partial erosion and talus formation due to waves, currents and weathering. The area from similar to 30 m to similar to 80 m depth shows gentle rises and falls, with a modest slope. Below similar to 80 m, the bathymetry gradually transitions to a relatively flat undulation with a smooth slope, extending to offshore areas. The bathymetry and the seafloor image from backscattering data show that there are small islets of the Dokdo volcano and a rocky sea bottom elongated from the islets, probably originating from residual parts of the eroded and collapsed main crater of the volcano. The seafloor images identify typical rocky bottoms, like rocky protrusions, and less sediment around the survey area, except for some areas with shallow sand sedimentary deposits. The stepped slopes of the study area are interpreted to be wave-cut submarine terraces rather than terraces from other origins, based on their relatively flat morphology and lack of sediments. The submarine terraces suggest a repetition of sea level changes (transgressions and regressions) in the Quaternary.