2000 Volume 52 Issue 52 Pages 5-12
High-resolution, three-dimensional submarine topographic mapping of Kaihara, a shallow marine sandridge, off Nogutsuna Island in the Seto Inland Sea, Japan was carried out using a narrow multibeam echo sounder SEABAT 8101. Through the mapping, two kinds of topographic features suggesting directions of sediment transport, such as subaqueous dunes and obstacle marks, were recognized. The dunes are seen on the southern part of Kaihara and show asymmetrical forms with steeper west-northwestern and northwestern slopes suggesting that the directions of sediment transport are west-northwestward and northwestward. In the northeastern part, three obstacle marks having E-W and WSW-ENE trends are seen to the west and west-southwest of artificial fish-gathering constructions. The directions of sediment transportation in this area are thus westward and west-southwestward. As a large submarine caldron is situated on the east of Kaihara and surface sediments become finer from the caldron to Kaihara, the sediments comprising the Kaihara sandridge are interpreted to have transported from the caldron by tidal currents, which are known as most likely agents of sediment transportation in the Seto Inland Sea, and accumulated where the currents dispersed and lost their energy.