BEDDED SHELL DEPOSIT AT AO NANG, KRABI PROVINCE, SOUTHERN THAILAND: A RECORD OF A PREHISTORIC TSUNAMI EVENT OR EXTREME STORM EVENT OR NEITHER

A one meter thick, bedded shell deposit, exposed on the west coast of Thailand, yielded radiocarbon ages of 1425 and 1410 AD. The bedded shell deposit is located in a foot cave at the base of a limestone headland at Ao Nang in Krabi Province on the west coast of Thailand. This deposit lies immediately above the modern high tide level and has been protected from erosion by its location in a foot cave and by rock fall debris in front of the foot cave. Because there is no evidence of a high sea level stand at 1400 AD, this bedded shell deposit is perhaps the result of a tsunami event or an extreme storm event that occurred around 1400 AD. With the information available it cannot be determined whether this deposit is from an extreme storm event or a tsunami event or perhaps neither because there is not an accurate historical record for this part of Thailand for this time period. However, if the bedded shell deposit is the result of a tsunami event, the 1425 to 1410 AD radiocarbon age of this deposit suggests a recurrence interval of about 500 to 600 years for a large magnitude tsunami event in this region of Southeast Asia.