Submarine Terrace in Dokdo Evidence of the Sea Level Change of the East Sea in the Quaternary

Abstract

The East Sea comprises three basins the Ulleung Basin in the southwestern part, the Yamato Basin in the southeastern part, and the Japan Basin in the northern part. Dokdo (Dok island), located in the northeastern part of the Ulleung Basin, is a large volcanic island. Dokdo has the height of about 2,100 m from the seafloor and the submerged flat summit (guyot type) from coast to about 200 m in the water depth. The diameter of the summit is more than 10 km. We have conducted the detailed bathymetry surveys in the coastal area and the northeastern part of the submerged summit area. The coastal area, within about 30 m water depth, are characterized by very complicated, steep sloping and irregular sea-surface topography. After about 30 m, the seafloor gradually becomes gentle, and the submarine terraces start to appear one by one. From the depth of about 80 m to the edge of the Dokdo volcano summit, it can be seen that flat topography and more gentle slopes. Submarine terraces in Dokdo are relatively flat, gently inclined surfaces with prominent scarps at the shoreward end. The inner edges of the terraces have much steeper than other flat seafloor. We interpreted the topographic features to be wave-cut submarine terraces based on their flat morphology, lack of sediment deposit, and no hard corals. The formation ranges of the main submarine terraces are 30 ~ 50 m, 60 ~ 80 m, 85 ~ 95 m, 100 ~ 105 m, 110 ~ 125 m, and 130 ~ is a large volcanic island. Dokdo has the height of about 2,100 m from the seafloor and the submerged flat summit (guyot type) from coast to about 200 m in the water depth. The diameter of the summit is more than 10 km. We have conducted the detailed bathymetry surveys in the coastal area and the northeastern part of the submerged summit area. The coastal area, within about 30 m water depth, are characterized by very complicated, steep sloping and irregular sea-surface topography. After about 30 m, the seafloor gradually becomes gentle, and the submarine terraces start to appear one by one. From the depth of about 80 m to the edge of the Dokdo volcano summit, it can be seen that flat topography and more gentle slopes. Submarine terraces in Dokdo are relatively flat, gently inclined surfaces with prominent scarps at the shoreward end. The inner edges of the terraces have much steeper than other flat seafloor. We interpreted the topographic features to be wave-cut submarine terraces based on their flat morphology, lack of sediment deposit, and no hard corals. The formation ranges of the main submarine terraces are 30 ~ 50 m, 60 ~ 80 m, 85 ~ 95 m, 100 ~ 105 m, 110 ~ 125 m, and 130 ~