情報館入口正面に展示中の「島原半島地形模型」についてご紹介します。

■ 島原半島とは
1周約120km、胃袋のような形をした半島で、そのつけ根の部分に渡り鳥の楽園だった「諌早干拓」がありました。半島は東西約24ｋｍ、南北約30ｋｍ。面積は452.84㎢になります。
中央に雲仙岳を据える半島は海に囲まれており、周辺の上昇気流によって雲が発生しやすく雲に覆われた日が多いとされています。特に6月の梅雨の時期は、霧が発生しやすく濃霧の日が多くなります。
この地域で耳にする「雲仙岳」という名称。これは、三岳五峰（さんだけごほう）の総称です。普賢岳（1,359m）、妙見岳（1,333m）、国見岳（1,347m）の三岳。周辺の山の野岳（1,142m）、絹笠山（870m）、矢岳（940m）、九千部岳（1,063m）、高岩山（871m）の総称。平成新山(1,483m)。
雲仙は「大山火山帯」と呼ばれる九州中央部を横断する断裂陥没地帯の一部です。「別府—阿蘇—雲仙」のように東西方向に走る大きな断層によって中央部が約２００ｍ落ち込んで、雲仙地溝が形成されています。
北側の千々石断層と南側の深江断層、布津断層、金浜断層が主な断層で、その間にも多くの断層があり断層の先には熊本県の阿蘇山があるとされています。
半島の西側。橘湾には円形の陥没地「千々石カルデラ」があり、約12km地下に雲仙火山のマグマ溜りがあります。これが雲仙一体に火山のエネルギーをもたらす源泉となっています。

★ 英語バージョン
　The Shimabara Peninsula is shaped by the movement of magma deep beneath the earth. Volcanoes have grown, erupted, collapsed, and grown again, creating the mountainous landscape of the peninsula. Beginning three-and-a-half million years ago, most volcanic activity was in the south and the west of this location, but about 500,000 years ago, volcanic activity suddenly shifted north, creating the oldest of the Unzen volcanoes. That eruption connected the volcanic island to the Kyushu mainland. This was the birth of the Shimabara Peninsula and the central mountains known collectively as Unzen-dake.

　Over the following 150,000 years, magma flow decreased. The center of the peninsula began to sink as parallel faults to the north and south slowly pulled the central region apart. The valley left behind a graben, a valley formed between two shifting tectonic faults. Within the last 150,000 years, many volcanoes formed lava domes in the Unzen graben. After releasing lava and pressure from below, these volcanoes would collapse into their own emptied magma chambers to form a “caldera,” which comes from the Spanish word for cauldron. This process created the Nodake Caldera between approximately 70,000 to 150,000 years ago. The cycle continued as Myōken volcano formed within this larger caldera, eventually collapsing after the eruption of nearby Kunimidake and Mayuyama in the tens of thousands of years that followed.

　Finally, what is left is what we can see and appreciate today: the Myōken Caldera. The rim of this ancient volcano forms a narrow trail with steep drops on either side. Beneath the surface, volcanic activity continues. To the east are Fugendake, Tateiwanomine, and Shimanomine, formed by consecutive eruptions 4,000 to 5,000 years ago. Looming above all these is Heisei Shinzan (1,483 m), the newest and highest of Myōken’s lava domes formed from 1991 to 1995. (351/250)

Sources:
Existing Geopark sign on-site: “Myōken Caldera and Lava Domes of Fugendake”
Geopark sign at Gamadas Dome: “Shimabara Peninsula has grown up by volcanic eruptions!”