Shimousa Plateau

A plateau stretching from central to northern Chiba Prefecture. Most of it is in Shimousa Province, including part of Kazusa Province. Together with the Kazusa Plateau spreading to the southeast, it is called the Ryoso Plateau, but because the topography of both the Kazusa and Shimousa Plateaus is identical, the Shimousa Plateau in the broad sense also includes the Kazusa Plateau. The plateau is about 30-40 meters above sea level, decreasing to the north, and drops into the Tone River lowlands with cliffs of 10-20 meters, facing the Edo River to the west. The eastern end of the plateau borders the Kujukuri Plain, and a steep cliff of 30-50 meters runs in a straight line parallel to the coastline of Kujukuri Beach. The topography was formed in the Quaternary Pleistocene (Pleistocene Epoch), with an old clay layer at the base of the plateau, the Narita layer of shallow sea deposits on top of that, and the Kanto Loam layer of red soil made of volcanic ash piled up to a thickness of 3 to 6 meters on top. Water is difficult to obtain, and in the early modern period, there were only a few old villages scattered here and there, as well as horse pastures such as the Kogane Gomaki and Sakura Nanamaki, which were directly managed by the Edo Shogunate. However, new agricultural settlements were created after the Meiji era when the area was developed to provide jobs for the samurai class, and Yachimata and Tomisato in the center of the plateau are large-scale farming areas with a high rate of full-time farmers. The western part of the plateau borders Tokyo across the Edo River, and urbanization is progressing, with residential and commercial areas expanding, but there are also suburban agricultural areas mainly focused on vegetable production.

Except in the suburbs of cities, land use is extensive, and large areas of land are available, so New Tokyo International Airport (now Narita International Airport) was opened in Narita City (1978), and large-scale development of Chiba New Town is underway in the northern part of Funabashi City, Shirai City, and Inzai City (project period 1969-2014).

[Yamamura Junji]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

千葉県の中部から北部にかけて広がる台地。その大部分が下総国に入っていて、上総(かずさ)国の一部が含まれる。南東に広がる上総台地とあわせて両総台地(りょうそうだいち)ともいうが、上総・下総両台地の地形面が同一のため、広義の下総台地には上総台地も含まれる。標高約30～40メートルで北に低くなっており、10～20メートルの崖(がけ)をもって利根(とね)川低地へと落ち込み、西は江戸川に面する。台地東端は九十九里平野に接し、九十九里浜の海岸線に並行して30～50メートルの急崖(きゅうがい)が直線状に続く。第四紀更新世（洪積世）に形成された地形で、台地下層に古い粘土層、その上に浅海堆積(たいせき)物の成田層が積もり、最上部に火山灰からなる赤土の関東ローム層が3～6メートルの厚さで堆積している。水が得にくく、近世には点在する古村のほか、小金(こがね)五牧、佐倉七牧などの江戸幕府直轄の野馬の放牧場が置かれていたにすぎないが、士族授産を目的とした明治以後の開拓によって新しい農業集落が発生し、台地中央部の八街(やちまた)、富里(とみさと)などは、経営規模が大きく専業率も高い畑作農業地域をなす。台地西部は江戸川を挟んで東京都と接し、都市化が進行して住宅地や商工業地が拡大しているが、野菜生産を主とした近郊農業地域も混在している。

　都市近郊を除いては粗放的な土地利用が行われており、広い土地が確保できるので成田市に新東京国際空港（現、成田国際空港）が開設（1978）され、また船橋市北部や白井(しろい)市、印西市にかけては千葉ニュータウンの大規模開発が進展（事業期間1969～2014）している。

［山村順次］

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