Shimabara Peninsula

A peninsula that juts out into the southeastern part of Nagasaki Prefecture. Administratively, it is made up of the cities of Shimabara, Minamishimabara, and Unzen. Most of it is made up of the Unzen volcanic group, with the Minamishimabara Plateau in the south, and its outline is elliptical, but the collapsed caldera of Tachibana Bay on the west side removes part of the ellipse. Topographically, on the eastern side of Shimabara Bay, a gentle volcanic fan extends into the sea, creating a sandy coastline, while on the west side, the volcanic group is cut by faults, creating an abundance of rocky coastlines. The Unzen volcanic group has developed faults running east-west, the most notable of which are the Chijiwa Fault Line in the north and the Kanahama Futsu Fault Line in the south, and between these fault lines is the Unzen Rift Valley. The Kinugasa, Kusenbu, and Unzen (hot spring) volcanoes erupt in this rift zone. The Obiyayama eruption crater is located where these three volcanoes meet, forming the basin-like Unzen Hot Springs.

Mount Unzen is an active volcano, and in 1657 (Meireki 3), the Furuyake lava flow erupted north of Mount Fugen (1,359 meters), and in 1792 (Kansei 4), the Shinyake lava flow erupted, causing a major collapse of Mount Mayu, and the mountain split open, causing a large landslide along with hot water. The volcano group forms several lava domes above 300 meters above sea level, and gentle volcanic fans below 300 meters above sea level, with the Aino, Azuma, Kunimi, and Ariake fans in the north, Shimabara, Fukae, and Arie fans in the east, and Tonosaka fans in the south. The Obama fault causes a lack of fans in the west, and Obama Hot Springs is located on the coast. Land use on the alluvial fan is characterized by the development of cattle ranching and dairy farming, as well as an increase in potato planting and an increase in mandarin orchards through conversion and reclamation of farmland. The Minamishimabara Plateau south of the Tobiko-Arima Line is a basalt lava plateau that erupted on the Tertiary strata; the plateau around Mount Hiko is well preserved, while the Uehara Plateau is mesa-shaped, and Mount Hojo and Mount Atago are butte-shaped. There are many springs at the boundaries between these plateaus and the Tertiary strata on the mountainside, and rice terraces have developed there, but it is also an area where landslides occur frequently. The coast is made up of gravel on the east coast and rocky coasts on the south and west coasts, and nori and wakame seaweed farming is thriving on the east coast. On the south and west coasts, pole and line fishing is the norm.

[Yasuyoshi Ishii]

"History of the Shimabara Peninsula, Volumes 1, 2 and 3, by Hayashi Senkichi (1954, Minamitaka District Educational Association, Nagasaki Prefecture)" ▽ "Ancient Culture of the Shimabara Peninsula - Overview and Chronology, edited by the Shimabara Historical Society (1962, Shimatetsu Kankosha)" ▽ "Shimabara Peninsula: A Land of Greenery and Sunshine" (1970, Nagasaki Prefecture Municipal Autonomy Promotion Association)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

長崎県南東部に突出する半島。行政上は島原市、南島原市、雲仙市(うんぜんし)からなる。大部分が雲仙火山群から成り立ち、南部に南島原台地を伴い、その輪郭は楕円(だえん)形を示すが、西側に橘(たちばな)湾の陥没カルデラがあって、楕円形の一部が欠けている。地形的には東側の島原湾側では、緩やかな火山性扇状地が海中にまで延びて、砂質の海岸が発達し、西側では火山群が断層によって切られ、岩石海岸の地形に富む。雲仙火山群には東西方向の断層が発達し、その顕著なものとして、北に千々石(ちぢわ)断層線、南に金浜布津(ふつ)断層線があげられ、これらの断層線の間に雲仙地溝帯がある。この地溝帯に絹笠(きぬがさ)火山群、九千部(くせんぶ)火山群、雲仙（温泉）火山群が噴出している。これら三つの火山群の接触する部分に帯山(おびやま)爆裂口があり、盆地状の雲仙温泉が形成されている。

　雲仙火山は活火山で、1657年（明暦3）普賢岳(ふげんだけ)（1359メートル）の北側に古焼(ふるやけ)溶岩流が噴出し、1792年（寛政4）新焼溶岩流の噴出とともに眉山(まゆやま)の大崩壊がおこり、山体は裂けて噴出した熱水とともに大地すべりを発生している。火山群は、標高300メートル以上では数峰の溶岩円頂丘をなし、標高300メートル以下では緩やかな火山性扇状地をなし、北部に愛野、吾妻(あづま)、国見、有明(ありあけ)、東部に島原、深江、有家(ありえ)、南部に塔ノ坂の各扇状地がある。西部には小浜(おばま)断層があって扇状地を欠き、海岸に小浜温泉がある。扇状地上の土地利用は、牧牛や酪農の進展のほかに、ジャガイモ作付けの増大と畑地転換や開墾によるミカン園の増大とが特徴的である。飛子(とびこ)―有馬線以南の南島原台地は、第三紀層上に噴出した玄武岩の溶岩台地で、彦山(ひこさん)周辺の台地面は保存が良好であるが、上原台地はメサ状、鳳上(ほうじょう)岳・愛宕山(あたごさん)はビュート状をなす。これらの台地と山腹の第三紀層との境界には湧水(ゆうすい)が多く、棚田が発達するが、地すべりの多発地帯をもなす。海岸は、東岸では砂礫(されき)海岸、南岸および西岸では岩石海岸をなし、東岸ではノリ、ワカメの養殖が盛んである。南岸および西岸では一本釣り、延縄(はえなわ)漁業を主とする。

［石井泰義］

『林銑吉著『島原半島史』上中下（1954・長崎県南高来郡教育会）』▽『島原史談会編『島原半島の古代文化――概説と年表』（1962・島鉄観光社）』▽『『緑と太陽の地　島原半島』（1970・長崎県市町村自治振興会）』

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