CAUSES OF POWERFUL STORM SURGES OF THE 18TH CENTURY CONFIRMED FROM HISTORICAL RECORDS AND THOSE IN COASTAL SEDIMENTS ON THE WEST COAST OF THE KOREAN PENINSULA

The extreme storm surge caused by Super Typhoon Haiyan (2013) may have resulted from high sea surface temperatures and a fluctuating climate system due to greenhouse effect. Therefore, paleo-climate research has been concentrated on hydrological activities in warm periods. However, according to the Annals of the Joseon Dynasty, which contains natural disaster records from 1413 CE to 1868 CE, such hydrological environments in warm periods cannot sufficiently explain the high frequency of storm events since the 18th century. The specific location and magnitude of a storm surge cannot be known from historical records; thus, it is necessary to find records in coastal sediments. A large difference between the tides is common in the west coast, and increases northward. If the strongest storm surge and the highest high water overlap, the flood damage to the coastal area will be the worst. A large number of Holocene storm surge records were unearthed from more than 50 boreholes in the tidal sediments and from trench sections of sand dunes in a 40-km section of the southern west coast of the Korean peninsula. Among them, two powerful storm surge records from 310 and 150 years ago, that report events occurring in different parts of the study area, were unearthed by analyses of grain size distribution, magnetic susceptibility, and the content of major and trace elements. Particularly, the evidence of a storm surge from 310 years ago was observed at 11.5 m a.s.l. on the trench section of a dune. Storm-floods from the 1600s to the 1800s were frequently reported in historical records (the Annals of the Joseon Dynasty and the Daily records of the Royal Secretariat). In particular, the record of an extreme storm surge occurring at the Optically Stimulated Luminescence (OSL) age of 310 years ago is almost consistent with the records of the historical events of 1713 CE and 1714 CE in the study area. We will discuss the reasons for the frequent occurrence of powerful storm surges not only in warm periods but also in the little ice age, using climatic factors. There is important national infrastructure in the study area, and if the same storm surge occurs again, serious accidents may ensue. Therefore, the storm surge records in the sediments are expected to contribute not only to the prediction of events but also to the mitigation of disasters.