Boso Peninsula

A large peninsula jutting out from the southeastern part of the Kanto region. It faces the Pacific Ocean to the east and south, and Tokyo Bay and the Uraga Channel to the west, and covers the entire area of ​​Chiba Prefecture. As a result of the Kanto Tectonic Basin Movement, the elevation decreases from south to north with the Boso Hills, Shimousa Plateau, Tone River, and Edogawa lowlands. The Tokyo Bay coast is made up of rivers such as the Yoro River, Obitu River, and Koito River that flow north through the Edo River and the Boso Hills, creating the Tokyo Bay coastal plain, while the Kujukuri Plain, an uplifted coastal plain, spreads out at the end of the Shimousa Plateau on the east side.

The Boso Hills are mainly composed of the Tertiary Miura Group and the Quaternary Kazusa Group, and the active east-west fault movement has resulted in complex intertwining of the strata, with the Kamogawa Lowlands and Tateyama Plain forming grabens, and the Mineoka Mountains forming basins. The Shimousa Plateau is a vast area of ​​land 30-40 meters above sea level, and is covered with a 3-6 meter thick layer of Kanto Loam red soil made from volcanic ash from the Fuji and Hakone volcanoes, and was left waterless for a long time. In the early modern period, the Koganegomaki and Sakura Nanamaki wild horse pastures were established here, and their development was encouraged after the Meiji period. Today, it functions as a vegetable production area in Chiba Prefecture, but the area has undergone significant changes, including the construction of New Tokyo International Airport (now Narita International Airport). The Tokatsu region in the northwest of the peninsula is undergoing urbanization with the development of Chiba New Town and other residential and industrial complexes. The Tone River lowlands are a water town, and with the reclamation of Lake Inbanuma and land improvement for rice paddies, it has become Chiba Prefecture's grain-producing region, producing early-season rice. Most of the sea surface from Urayasu City to Futtsu City on the Tokyo Bay coast has been reclaimed, forming the Keiyo coastal industrial area, but on the other hand, recreational areas such as seaweed and shellfish farms, swimming beaches and clam-digging areas have disappeared. As a result, artificial beaches have been constructed on the coasts of Inage in Inage Ward and Makuhari in Hanamigawa Ward in Chiba City, restoring places for citizens. The Kujukuri Plain had been plagued by droughts, but with the completion of the Otone Irrigation Canal and the Ryoso Irrigation Canal, rice cultivation has stabilized, and new avenues of life have been found in greenhouse horticulture, gardening, pig farming, etc. The coastline is lined with the long Kujukuri Beach and the rocky coasts of the Uchibo and Sotobo, and offshore fishing, coastal fishing along the rocky shores, and floriculture are thriving, and the tourism industry has been revitalized with the development of swimming beaches and tourist facilities.

[Yamamura Junji]

"The Boso Peninsula by Toshio Kikuchi (1982, Daimeido)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

関東地方南東部に大きく突き出た半島。東と南は太平洋、西は東京湾と浦賀水道に面し、千葉県の全域である。関東構造盆地運動の結果、南から北へ房総丘陵、下総台地(しもうさだいち)、利根川(とねがわ)と江戸川の低地と高度は低くなっていく。東京湾岸は江戸川や房総丘陵を北流する養老川、小櫃川(おびつがわ)、小糸川などの河川がつくる東京湾沿岸平野があり、一方、東側の下総台地末端には隆起海岸平野の九十九里平野が広がる。

　房総丘陵はおもに第三紀三浦層群や第四紀上総(かずさ)層群からなり、東西方向の断層運動が活発で地層が複雑に入り乱れ、加茂(かも)川低地や館山(たてやま)平野は地溝、嶺岡(みねおか)山地は地塁をなす。下総台地は標高30～40メートルの広大な土地で、富士・箱根火山の噴出した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(たいせき)し、水なしの地として長く放置されていた。近世、小金五牧(こがねごまき)、佐倉七牧の野馬放牧場が置かれ、明治時代以後はその開拓が奨励された。今日千葉県における野菜生産地域として機能しているが、新東京国際空港（現、成田国際空港）の建設もあって地域変化が著しい。半島の北西部、東葛(とうかつ)地域は千葉ニュータウンをはじめ住宅地、工業団地が開発され都市化が進行している。利根川低地は水郷をなし、印旛沼(いんばぬま)の干拓や水田の土地改良がなされ、千葉県の穀倉地帯となっており、早場米が生産される。東京湾岸の浦安市から富津(ふっつ)市に至る海面のほとんどは埋め立てられ京葉臨海工業地域が形成され、反面、ノリと貝の養殖場、海水浴場や潮干狩場などのレクリエーション地が消滅した。そこで千葉市稲毛(いなげ)区稲毛、花見川区幕張(まくはり)の地先海岸にそれぞれ人工海浜が造成され、市民の憩いの場が復活した。九十九里平野は干害に悩まされてきたが、大利根用水、両総(りょうそう)用水の完成によって米作は安定し、さらに施設園芸、植木、養豚などに新たな活路をみいだしている。海岸線は長大な九十九里浜や内房(うちぼう)、外房(そとぼう)の岩石海岸が続き、沖合漁業や磯根(いそね)の沿岸漁業、さらに花卉(かき)栽培が盛んで、また、海水浴場や観光施設が整備されて観光産業が活発化している。

［山村順次］

『菊地利夫著『房総半島』（1982・大明堂）』

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