Holocene sea levels along the Andaman Sea coast of Thailand

Abstract

For the Malay-Thai Peninsula several sea-level curves for the younger Holocene, based on field evidence as well as on hydro-isostatic modelling of a far-field site, have been published. The general assumption is a rapid rise to a mid-Holocene maximum up to +5 m above present sea level, followed by a constant or oscillating regression. However, from the Andaman Sea coast of Thailand, which was affected by the 2004 tsunami, only isolated observations are available regarding Holocene sea levels. Thus, the timing and magnitude of the Holocene highstand as well as the course of the regression remain to be defined. As several palaeotsunamis could be detected in the meantime it is important to know the related sea levels as exactly as possible to judge the energy, inundation width and potential wave height of these events. Therefore, fixed biological indicators from the rocky coasts of the Phang-nga Bay and Phuket, as well as morphological indicators from beach-ridge and swale sequences along the exposed west coast (Ko Phra Thong) were studied, to gain information about the Holocene sea-level development in this region. While oyster and coral data from the Phang-nga Bay and Phuket document a Holocene maximum of +2.6 m at 5700 cal. BP, the ridge crests and swale bases in the northwest of the study area point to maximum heights of +1.5–2.0 m above the present level around 5300 years ago. During the last 3000 years, to when the largest part of the Holocene palaeotsunami deposits from Thailand was dated, relative sea levels (RSL) in both areas did not exceed +1.5 m.