蘭陽溪流域系統千年來自然災變與淇武蘭文化空白之關聯
Other Title
Linkage between Natural Disasters and Kiwulan Cultural Hiatus over the Last 1000 Years in the Lanyang Drainage System
Date Issued
2011
Abstract
Active tectonic activities and frequent typhoon visits make Taiwan unique in having very high rates of uplift, precipitation, denudation and sedimentation. Particularly, intense rainfall associated with typhoons often causes natural disasters in river systems, such as flooding, large-scale landslides and debris flows, affecting human activities at the present time and in the past. Typhoon Morakot in 2009 may serve as a modern analog of such events in the geological past.
Site Kiwulan is a newly discovered archaeological site of the Iron Age in Lan-Yang Plain. A cultural hiatus, found around 1200-1500 cal. yr AD, suggests that the settlement was once abandoned. It remains a mystery what caused this abandonment.
This study assembles radiocarbon dates of upland river terraces, organic proxies in flood plain lake sediments and content of wood shreds in nearby marine sediment core. These records are synthesized to infer the frequency and magnitude of ancient floods over the past millennium in the Lan-Yang River system in northeastern Taiwan.
Alluvial fan terraces distributed along the banks of upper Lan-Yang River are considered to be remains of ancient debris flow events, and their radiocarbon dates fall in two time ranges: 850-1100 and 1400-1600 cal. yr AD. Organic proxies such as TOC and C/N ratio representing terrestrial plant input were measured from bulk sediments of Lake Dahu and Lake Meihwa in the Lan-Yang Plain. Peak values of TOC, C/N ratio and organic indicator plus optical and radiographic images from ITRAX-XRF core scanner are conspicuous during 900-950, and 1400-1500 cal. yr AD, implying frequent flood events. Abundance peaks of wood shreds in marine box core ORI-801-7A occurred during 950-1050 and 1450-1550 cal. yr AD, coinciding with those terrestrial input events recorded in lake sediments.
In summary, different lines of evidence collected from the Lan-Yang River system suggest that flood events were more frequent during two particular periods: 900-950 cal. yr AD and 1400-1500 cal. yr AD. The later period corresponds to the cultural hiatus at Site Kiwulan, suggesting that the lost civilization may be related to severe and frequent flooding of the Lan-Yang Plain during that period.
Subjects
Lan-Yang River
flood
natural disasters
organic proxies
XRF core scanner
Kiwulan
Type
thesis
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