Prehistorical frequency of high-energy marine inundation events driven by typhoons in the Bay of Bangkok (Thailand), interpreted from coastal carbonate boulders

© 2016 John Wiley & Sons, Ltd. Rapidly rising populations of low-lying megacities in Asia mean that understanding the potential risk of coastal flooding by storm surge is of paramount concern. The city of Bangkok and the wider Chao Phraya River delta at the head of the Gulf of Thailand is a region topographically vulnerable to coastal flooding, but without the record of a high-energy marine inundation (HEMI) event in historical time owing to the atypical path that a typhoon must take to be able to produce such an event. This work builds upon previous findings that identified coastal depositional evidence for HEMI events in the form of coastal carbonate boulders (CCBs) located on Ko Larn Island in the eastern Bay of Bangkok. The HEMI events were most likely driven by typhoons and the CCBs are therefore interpreted as typhoon deposits. Through uranium/thorium dating, it is revealed that from ad 1400 to ad 1600 the Bay of Bangkok possibly experienced a phase of relatively heightened storm impact. During this period, the frequency of typhoon-driven HEMI events was approximately four events in 200years. Waves generated onshore minimum flow velocities (MFVs) in excess of 5m/s. Such exceptional MFVs are unlikely to be produced during the annual northeast monsoon, but are consistent with typhoon-impacted coastlines elsewhere in the tropical Asia-Pacific region where similar CCB evidence exists. Since ad 1600, the Bay of Bangkok has enjoyed a relatively quiescent phase, recording less frequent HEMI events and of lower magnitude. However, the re-occurrence of a typhoon-driven HEMI event on the scale of the prehistorical events that emplaced carbonate boulders at elevation on Ko Larn Island would threaten low-lying coasts in the Bay of Bangkok, including the Chao Phraya delta, with potentially damaging inundation