Kantō Plain

The Nihongo|Kantō Plain|関東平野 is the largest plain in Japan located in the Kanto Region of central Honshū. The total area 17,000 sq km covers more than half of the Region extending over Tokyo, Saitama Prefecture, Kanagawa Prefecture, Chiba Prefecture, Gunma Prefecture, and Tochigi Prefecture. [ Encyclopedia of Japan, Kōdansha]

The northern limit borders on the Abukuma Highlands, Yamizo Mountain Range, Ashio Mountain Range, and a volcanic field associated with the Nasu Volcanic Belt. The western coincides with the Kantō Mountain Range and the southern edge is defined by the Bōsō Peninsula, the Miuraryō Hills, Tokyo Bay, and Sagami Bay. The Kashima Sea and Kujūkuri Beach define the eastern end of the plain. Most of the rivers originate in the northern or western mountain ranges and flow east or southeast into the Pacific Ocean, Tokyo Bay, or Sagamiryō Bay. In the central part of the plain is the Tone River; in the northern part the Watarase River, Kinu River, Kokai River, Naka River, and Kuji River; and in the southern part the Arakawa River, Tama River, Sagami River, and Sakawa River. Of these rivers, the Tone River encompasses a large area of floodplain, for it has the largest drainage area in Japan of 16,840 sq km. The drainage areas covered by these rivers account for the alluvial lowland of the Kanto Plain. [ Encyclopedia of Japan Tokyo: Kōdansha]

A collection of plateaus constitute a large part of the plain. Among them are the Ōmiya, Musashino, Sagami, and Jōsō Plateaus. These large plateaus are divided into smaller ones by shallow river valleys. One of the common features of the plateaus is that their surfaces are covered with a thick layer of loam of volcanic origin. Volcanic ashes from surrounding volcanoes, Mounts Asama, Haruna, and Akagi to the north and Mounts Hakone and Fuji to the south, are thought to have been deposited on these plateaus. [ Nihon Daihyakka Jiten, Shōgakkan ] Among the plateaus, the Musashino Plateaus has the largest stretch of land, extending from the western edge of Oume to the eastern edge of Yamanote which borders alluvial plains of the Arakawa and Sumida Rivers. Its elevation gradually declines from west to east, measuring 190 m at Oume and 20 m at Yamanote. [ Nihon Daihyakka Jiten, Shōgakkan ]

Hills in the Kantō Plain stand on Tertiary strata and rise higher than surrounding plateaus, exemplified by the Sayama Hills and Tama Hills, typically, undulating between 100 and 200 m above sea level. Hills located at the western edge of the Kantō Plain, the Hiki Hills, Koma Hills, Kusahana Hills, and Kaji Hills, also reach approximately 200 m above sea level. [ Encyclopedia of Japan Tokyo: Kōdansha]

What is noteworthy is the overall tilt of the plateaus and hills. In general, the whole area is slightly bent and forming a basin centered in the Tone River and Tokyo Bay. The ongoing process of tectonic extension continues as the plain’s central region gradually sinks. [ Encyclopedia of Japan Tokyo: Kōdansha]

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