Miyakejima

It is an active volcanic island belonging to the Miyake Branch Office of Tokyo and has one village on the entire island. It is oval in shape, 7-10 km in diameter, and has an area of ​​about 55.50 square kilometers, making it the third largest island in the Izu Islands. It is part of the former Fuji Volcanic Belt and the East Japan Volcanic Belt, and is a stratovolcano made mainly of basalt. The highest peak is the central crater cone, Mt. Oyama (altitude 813 meters, but the summit disappeared in 2000 and is now 775 meters). There are records of 15 eruptions from 1085 (Otoku 2) to 1983, and in addition to the summit eruption at Mt. Oyama, there have been many radial fissure eruptions on the mountainside and the nearby seabed, and lava flows are also likely to occur, causing devastating damage with each eruption. The 1962 (Showa 37) eruption after World War II is known for evacuating schoolchildren off the island, and the 1983 eruption caused lava flows to bury and burn about 70% of the west coast village of Ako. The 2000 (Heisei 12) eruption created a caldera at the summit and released large amounts of toxic volcanic gas, leading to the evacuation of the entire island for about four and a half years from September of that year.

In June 2000, seismic activity increased, and on the 27th of that month, a small undersea eruption occurred, and strong earthquakes began occurring in the direction of Kozu and Niijima outside the island. On July 8th, the summit suddenly collapsed, and a phreatomagmatic explosion occurred. The collapse of the summit continued until early August, and the 1.6 km diameter Oyama caldera appeared. This collapsed caldera was formed when magma moved underground in the direction of Kozushima, creating a cavity underground. The largest eruption occurred on August 18th, and low-temperature pyroclastic flows occurred on August 29th. An evacuation order was issued for the entire island on September 2nd, forcing the islanders to live in evacuation for a long period of time. The evacuation order was lifted on February 1st 2005, and the island resumed accepting tourists in May of the same year, but sulfur dioxide gas continues to be emitted from Oyama. Volcanic activity is observed by the Tokyo Metropolitan Government, the Geospatial Information Authority of Japan, the National Research Institute for Earth Science and Disaster Prevention, and others.

There is a legend that Kotoshironushi no Mikoto crossed over to Miyakejima and ruled the nearby islands. The island's name is said to have originated from Miyakejima, or Imperial Family Island, as there are 12 shrines listed in the Engi Shiki. There is also a theory that it is because Tajihi no Mahito Miyakemaro was exiled there in the 8th century. During the Edo period, it was a place of exile. In Izu, a settlement on the northwest coast, there are ruins from the Suwada period of Yayoi culture, as well as the graves of Ikushima Shingoro, an actor involved in the Ejima incident, and Takeuchi Shikibu, a scholar of Japanese classics. There are as many as 230 species of wild birds. Fishing and seaweed harvesting are thriving here, and other specialties include spiny lobsters, turban shells, butter, camellia oil, boxwood crafts, and shiitake mushrooms. The area is home to the Tairo Pond, an explosion crater lake, and is a beautiful place with beautiful scenery. It is part of the Fuji-Hakone-Izu National Park. The population is 2,791 (2009).

[Akira Suwa and Setsya Nakata]

"Miyakejima History Compilation Committee's 'Miyakejima History' (1982, Miyake Village)" ▽ "Miyakejima History and Folklore, by Nobumichi Ikeda (1983, Dento to Gendaisha)" ▽ "A Year in the Life of the Miyakejima Islanders, by Akira Mitani (2001, Iwanami Shoten)" ▽ "Miyakejima: The Thorny Path of Evacuation from the Volcanic Eruption - A Record of Four Years Since Then, by Sakae Murae (2005, Bungeisha)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

東京都三宅支庁に属し、全島1村の活火山島。長円形で径7～10キロメートル、面積約55.50平方キロメートルで、伊豆諸島では面積第3位。かつての富士火山帯、東日本火山帯に属し、おもに玄武岩の成層火山である。最高峰は中央火口丘の雄山(おやま)（標高は813メートルであったが、2000年の噴火活動で山頂部が消滅し、現在は775メートル）。1085年（応徳2）を皮切りに1983年まで15回の噴火の記録があるが、雄山での山頂噴火のほか、山腹～付近海底での放射状の割れ目噴火が多く、溶岩流も生じやすく、噴火のつど惨害を出した。第二次世界大戦後の1962年（昭和37）噴火は学童の島外疎開で知られ、1983年噴火では溶岩流が西海岸の集落阿古(あこ)の約7割を埋没・焼失させた。2000年（平成12）噴火では、山頂にカルデラが生じるとともに多量の有毒火山ガスが放出したため、同年9月から約4年半の全島避難が続いた。

　2000年6月地震活動が活発化、同月27日に海底で小噴火がおこり、強い地震が島外の神津(こうづ)・新島(にいじま)方面で発生し始めた。7月8日には突然山頂部が陥没するとともに水蒸気～マグマ水蒸気爆発がおきた。山頂部の陥没は8月初めまで続き、直径1.6キロメートルの雄山カルデラが出現した。マグマが地下で神津島方向に移動して、地下に空洞ができたために生じた陥没カルデラである。8月18日に最大規模の噴火があり、8月29日低温火砕流発生、9月2日全島避難指示が出され、島民は長期の避難生活を余儀なくされた。2005年2月1日避難指示は解除、同年5月より観光客の受入れを再開したが、雄山からは亜硫酸ガスの噴出が続いている。火山活動の観測は東京都、国土地理院、防災科学技術研究所などによって行われている。

　三宅島には事代主命(ことしろぬしのみこと)が渡島し、付近の島々を治めたという伝説があり、12の延喜(えんぎ)式内社があることから宮家(みやけ)島といったのが島名の起源という。また8世紀に多治比真人三宅麿(たじひのまひとみやけまろ)が流されたことによるとの説もある。江戸時代は流刑地。北西海岸の集落伊豆には弥生(やよい)文化の須和田式期の遺跡、絵島(えじま)事件の役者生島(いくしま)新五郎や国学者竹内式部(たけのうちしきぶ)の墓などもある。230種もの野鳥がいる。漁業やテングサ採取が盛んで、イセエビ、サザエや、バター、ツバキ油、ツゲ細工、シイタケなども特産であった。爆裂火口湖の太路(たいろ)池などもあり、山紫水明で、富士箱根伊豆国立公園に属す。人口2791（2009）。

［諏訪　彰・中田節也］

『三宅島史編纂委員会『三宅島史』（1982・三宅村）』▽『池田信道著『三宅島の歴史と民俗』（1983・伝統と現代社）』▽『三谷彰著『三宅島島民たちの一年』（2001・岩波書店）』▽『村栄著『三宅島　噴火避難のいばら道――あれから4年の記録』（2005・文芸社）』

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