A FLUVIALLY-DERIVED FLOOD DEPOSIT DATING TO THE KAMIKAZE TYPHOONS IN KAWAHARA, JAPAN

Historical records tell of the Kamikaze typhoons: two intense tropical cyclones that protected Japan from the Mongol invasions in 1274 and 1281 CE. The historical accounts of these typhoons, combined with sediment reconstructions, supply substantial evidence that these events are the most significant floods recorded in the past 2000 years. Flood reconstructions from two coastal back-barrier lakes in western Kyushu, lakes Daija and Kamikoshiki, show two prominent deposits dating to the late-13^th century that exhibit characteristics consistent with extreme coastal flooding (e.g. the deposits thin landward and are enriched in marine-derived material). However, the cause of these deposits is uncertain because Japan is vulnerable to coastal flooding from both typhoons and tsunamis, and it is difficult to distinguish between typhoon and tsunami-derived deposits in back-barrier lake sediments. To provide additional insight into the region’s flood history, we present a 3000-year sediment reconstruction from Lake Kawahara, a coastal back-barrier lake 40 km north of lake Daija. A shore-normal transect of cores from Kawahara reveal a prominent deposit that similarly dates to the late-13^th century but does not display features consistent with marine coastal flooding. The deposit thickens landward, and elemental analyses suggest that the deposit is fluvially derived. New diatom results suggest that the lake environment changed distinctly through the sediment record, and support a fluvial deposit. Given that a typhoon is more likely to cause terrestrial flooding than a tsunami, these results contribute to the growing line of evidence for extreme flooding from the land and sea in the late-13^th century by the Kamikaze typhoons.