2022 Volume 17 Issue 1 Pages 1-11
This study presents the development of sandbars in the Nakhon Si Thammarat coastal plain of southern Thailand in the late Holocene. Sandbars in the plain are Pleistocene sandbar-X, Holocene sandbars as sandbar-I, -II, and -III, and buried Holocene sandbar-Y. Sandbar-I extends about 80 km from north to south. Sandbar-II develops east of sandbar-I, with a length of about 25 km. The most recent sandbar-III is located along the current shoreline and extends to the north. Buried sandbar-Y extends from the area around Mt. Phrabat to the south. Pleistocene sandbar-X in the western part of the coastal plain develops clearly and diverges in its southern part. Radio-carbon dating of the lower peat layers behind the sandbar-I indicate around 7,500 cal BP. Peat layers around the Lake Noi located behind the sandbar-Y indicate similar ages but the peat layer is overlain by muddy sediments. Based on the spatial shape of sandbars-X, -I, and -II, and buried sandbar-Y, they developed in the direction from north to south. Sandbar-III, however, developed from south to north. This reverse direction of sandbar development is due to the change in wave or littoral current conditions after 1,500 cal BP.
