著者
稲崎 富士 太田 陽子 丸山 茂徳
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.123, no.4, pp.401-433, 2014-08-25 (Released:2014-09-01)
参考文献数
52
被引用文献数
4 8

River improvement works in the Kanto Plain have long history of over 400 years. Rice-paddy development in the Kanto Plain was significantly delayed compared to that in other plains including the Osaka Plain and the Nobi Plain. This was because of the difficulty in constructing an irrigation and drainage network, and protecting rice paddies from inundation. Therefore, the Tokugawa government started river improvement works in the Kanto Plain just after Tokugawa settled in Edo in 1590, and the works continue now. The flow of the Tone River into Tokyo Bay was originally blocked by uplands, but was finally rerouted to Choshi, 90 km east to the original mouth. The Ara River was also rerouted to the south. The purpose of rerouting was not only to reduce the risk of flooding in Edo city, but also to develop a waterway network for rice paddies to expand in the central Plain. Moreover, rerouting and connecting the Tone River with the Edo River enhanced the inland waterway transportation network of the Kanto Plain. Accordingly, a number of riverside towns, or Kashi, grew as nodes of the network. Small sailing ships and flatboats were the major conveyors of products. During the Meiji era, which followed the Edo period, canals were constructed and steamboats were introduced to replace sailing ships, at a time when water transportation was peaking. The inland waterway soon began to be replaced by present-day economic transportation systems such as rail and road. The central Kanto Plain was featured consistently by a subsiding basin through the Quaternary. Although the entire Plain was uplifted, Tokyo Bay, at the center of the Kanto Plain, sank over 1000 m. In contrast, the outer margin of the plain was uplifted 50 to 1000 m. Choshi, at the mouth of the present Tone River, is in the uplifted area. In contrast, the lower reaches of the River are at the northern extent of the subsiding basin. This is the reason why back swamp lakes or an estuary such as Kasumiga-ura and the ancient Katori-no-umi were formed in the area. Such crustal movements in the Kanto Plain continued throughout the Quaternary. Hydration and dehydration of two plates lying beneath this region were the driving force. Hydration of mantle peridotite underneath the Kanto Plain due to dehydration of the underlying Philippine Sea Plate (PHS plate), subducting from south to north 30-60 km deep (2 cm/year), causes volumetric expansion particularly at the marginal zone of the overlying plate (North American (NA) Plate). Serpentinized peridotite, produced above the Pacific Plate (PAC plate), which subducts from east to west under the PHS and NA plates, expands like popcorn and results in uplifting of the Boso Peninsular (non-volcanic outer arc) . In contrast, the sinking of the Tokyo Bay area is explained by the overlapping of the fore arc basin towards the PHS and PAC plates. From the viewpoint of tectonics, the sinking belt including Tokyo Bay is in a physical field where a sedimentary basin formed under tensile stress in the NE-SW direction. Small mantle convection caused by serpentinization of the uppermost mantle beneath the fore arc is the key to understanding the tectonic setting of the Kanto Plain.

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家康の江戸入府以降、利根川東遷から首都圏外郭放水路の設置にいたるまでを日本史上最大の土木事業とみなした論文があり、自然史的、歴史的概要を知ることができる https://t.co/Ngn4zg3JJO
「400年を越えて続いた日本史上最大最長の土木事業―関東平野における河川改修事業を規制したテクトニックな制約―」地学雑誌 https://t.co/a1UkjYz21h 関東河川改修の通史と、その自然地理学的な背景について。
@e_ikuon @hikisimousa @medieval_oota 既にご確認になっているかも知れませんが、17世紀初頭には、利根川が古隅田川を通っていたとする文献がありましたので、置いておきます。 https://t.co/BCElfLehxu https://t.co/vuq7vWMOjR
ほか、ご紹介いただいた論文。 関東平野の河川のつけかえと、それが発生した地質学的な背景について。 400年を越えて続いた日本史上最大最長の土木事業 https://t.co/QtLtcPZS9X

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