VERTICAL CHANGE IN SEDIMENT COMPOSITION IN THE NORTHERN PART OF KAGOSHIMA BAY

Kagoshima Bay, which is located at the southernpart of Kyushu Island, is composed of innermost (Aira caldera) and central (Ata caldera) basins. Innermost basin is connected by only one narrow channel, called Nishi Sakurajima Channel since an eruption of Mt. Sakurajima in 1914, that connected Mt. Sakurajima with Ohsumi Peninsula and closed Sakurajima-seto channel. In addition, expansion of Kagoshima Port makes the channel narrower. As a result, current system, which controls water quality in the bay, might be changed. Direct measurement of current system is difficult in the bay, therefore bottom sediment sampling is applied to estimate the current system. The bottom samples for this study were collected perpendicularly from 24 stations at the area of Nishi Sakurajima Channel to Off Hayato Santo. This study reveals that the current system in innermost basin is composed of three major current systems.