Extreme flood events and their frequency variations during the middle to late-Holocene recorded in the sediment of Lake Suigetsu, central Japan

Abstract

Many studies are reconstructing flood records in the continental margins during the middle to late-Holocene. However, distinguishing the frequency and magnitude of flood events was difficult. Light gray event layers (GELs) in the sediment of Lake Suigetsu in Central Japan can solve this problem because they are recording the occurrence and magnitude of flood events during the last 80 years. Using these GELs, we aimed to reconstruct the frequency and magnitude of flood events during the last 8000 years. First, we verified whether GELs maintained the recording of flood events. We found that thin GELs (less than 40 mg/cm2 in mass) were rare, probably because of bioturbation, whereas thick GELs (larger than 40 mg/cm2 in mass) were rarely erased. We also found that GELs formed by the same amount of rainfall could have been thinner before 100 years ago. We revealed that the occurrence of extreme flood-origin event layers (EFELs: GELs thicker than 40 mg/cm2) during the last 8000 years may indicate the occurrence of extreme flood events (EFEs). Mass accumulation of EFELs may indicate the minimum estimation of rainfall on EFEs. There are several periods with higher frequency and magnitude of EFEs than those of the present level, agreeing with the periods of high flood activity in western Japan and East China. The frequency and magnitude of EFEs show different temporal variations. Northward and southward shifts in the westerly jet and monsoon fronts can partially explain such patterns.

History of Mid- and Late Holocene Palaeofloods in the Yangtze Coastal Lowlands, East China: Evaluation of Non-Pollen Palynomorph Evidence, Review and Synthesis

“…Minerogenic sediment layers in recent floodplain facies correspond closely with high magnitude flood events, as at Tongling and Nanjing in the lower Yangtze area [156], and will have done so in this area in the past [117,160,169], as has been shown in other regional studies of Holocene flood histories (e.g. [41,43,47,148,170]).…”

“…While moderate annual seasonal Yangtze flooding has been a constant factor, introducing fine-grained minerogenic sediment into the floodplain sequence, major floods have occurred regularly throughout the Holocene, continuing into modern times [34,35], with periods during which very extreme flood events affected the Taihu lowlands as well as many other parts of the Yangtze valley [36,37]. Such extreme flooding events were not confined to the Yangtze, although the huge Yangtze catchment and river water discharge rates would exacerbate them, and have been recorded throughout eastern Asia, as in north China [38][39][40][41][42][43][44][45], Japan [46,47] and Korea [48][49][50]. As the timings of the major flooding phases in all these places correlate closely, it is clear that a regional external driver of extreme freshwater flooding has been involved, with some periods during the Holocene particularly affected.…”