Izu Islands

Japanese: 伊豆諸島 - いずしょとう

A volcanic archipelago belonging to Tokyo. A group of islands that stretch from the southeast of the Izu Peninsula in a roughly north-south direction in the Pacific Ocean. In addition to the main islands, the Izu Seven Islands (Oshima, Toshima, Niijima, Kozushima, Miyakejima, Mikurajima, and Hachijojima), the group also includes Aogashima Island, Bayonnaise Islands, Sumisujima, Torishima, and Sofuiwa Islands further south, as well as the affiliated islands of Udonejima, Jinaijima, Shikinejima, Tadanaejima, Onbasejima, Onoharajima, Inambajima, and Hachijokojima. The total area is 297 square kilometers, with a population of about 30,000. It is divided into three branch offices: Oshima, Miyake, and Hachijo, and two towns and six villages.

[Kikuchi Masao and Suwa Akira]

Nature

Divided into two systems based on topography and geology, Oshima, Toshima, Miyakejima, Mikurajima, Hachijojima, Aogashima, and Torishima are compound stratovolcanoes made of dark basalt to andesite. Niijima, Shikinejima, and Kozushima are whitish rhyolite. Myojinsho, a new volcanic island that emerged from an undersea eruption in 1952-1953 (Showa 27-28), is made of dacite. Oshima Miharayama, Niijima, Kozushima, Miyakejima, Hachijo Nishiyama, Aogashima, Myojinsho, Sumisujima, and Torishima are active volcanoes. The highest elevations of each island are 758m for Oshima, 508m for Toshima, 109m for Shikinejima, 572m for Kozushima, 814m for Miyakejima, 851m for Mikurajima, 854m for Hachijojima, and 423m for Aogashima. However, because the sea offshore is over 2000m deep, the islands can be considered volcanoes with a relative elevation from the seabed of 3000-4000m. The coastlines of Niijima, Shikinejima, and Kozushima are complex due to the plateau-like volcanic topography, but Toshima, Mikurajima, and Aogashima are surrounded by cliffs and are the most difficult islands to reach by boat. As the Kuroshio Current flows through the coastal waters, the climate is subtropical with high temperatures and heavy rainfall, and the vegetation is also distinctive. Toshima in particular has many large camellia trees, while Mikurajima has many large mulberry and boxwood trees.

[Kikuchi Masao and Suwa Akira]

History and Industry

These islands belonged to Izu Province in the past, but in the early modern period they came under the direct control of the Edo Shogunate. In the Meiji Period, the jurisdiction of the islands changed several times, but in 1876 (Meiji 9), they were incorporated into Shizuoka Prefecture, and in 1878, they were incorporated into Tokyo Prefecture. From the Middle Ages to the early modern period, the Izu Seven Islands were also a penal colony, and many exiled people were sent there, which had an impact on the society of the islands. Currently, there are ships from Tokyo, Atami, and Shimoda, as well as flights from Haneda Airport to Oshima and Hachijojima, and from Chofu Airport to Oshima, Niijima, Miyakejima, and Kozushima, but in general, the islands are not blessed with good transportation. This has affected industry, and the remoteness of the islands has always made it difficult to commercialize products, which have traditionally been dependent on agriculture, forestry, and fisheries. There are specialty products such as dairy farming on Oshima, camellia oil, the traditional industry of grass on Niijima since the early modern period, and the silk silk that gave Hachijo its name, formerly called Hachijo silk, but these have not grown to the extent that they are enough to support a living. However, in recent years, this region has been recognized as valuable as a tourist resource, with natural beauty such as the changing volcanic landscape, abundant flora, and beautiful coastline overlooking the Kuroshio Current, as well as historical vestiges dating back to the Middle Ages that can be seen everywhere, and in 1964 (Showa 39), it was incorporated into Fuji-Hakone-Izu National Park, and is now a place visited by many tourists.

[Kikuchi Masao and Suwa Akira]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

東京都に属する火山列島。伊豆半島の南東部からほぼ南北方向に太平洋上に並ぶ島嶼(とうしょ)。主島の伊豆七島（大島、利島(としま)、新島(にいじま)、神津島(こうづしま)、三宅島(みやけじま)、御蔵島(みくらじま)、八丈島(はちじょうじま)）のほか、さらに南の青ヶ島、ベヨネース列岩、須美寿島(すみすじま)、鳥島(とりしま)、孀婦岩(そうふいわ)や、属島の鵜渡根(うどね)島、地内(じない)島、式根島(しきねじま)、祗苗(ただなえ)島、恩馳(おんばせ)島、大野原島、藺灘波(いなんば)島、八丈小島などを含む。総面積297平方キロメートル、人口約3万。大島、三宅、八丈の3支庁、2町6村に分かれている。

［菊池万雄・諏訪　彰］

自然

地形、地質から2系統に分けられ、大島、利島、三宅島、御蔵島、八丈島、青ヶ島、鳥島は黒っぽい玄武岩～安山岩からなる複式の成層火山。新島、式根島、神津島は白っぽい流紋岩である。1952～1953年（昭和27～28）に海底噴火で出没した新火山島の明神礁(みょうじんしょう)は石英安山岩。大島三原山、新島、神津島、三宅島、八丈西山、青ヶ島、明神礁、須美寿島、鳥島は活火山。各島の最高標高は、大島758メートル、利島508メートル、式根島109メートル、神津島572メートル、三宅島814メートル、御蔵島851メートル、八丈島854メートル、青ヶ島423メートルであるが、近海が2000メートルを超える深海であるから、基底の海底からの比高は3000～4000メートル級の火山といえる。海岸線は、新島、式根島、神津島は台地状火山地形のため複雑であるが、利島、御蔵島、青ヶ島は周囲が断崖(だんがい)絶壁で諸島中もっとも船着きの悪い島である。近海を黒潮が流れるため、気候は高温多雨の亜熱帯性気候で、植生にも特色がみられる。ことに利島にはツバキ、御蔵島にはクワやツゲの大木が多い。

［菊池万雄・諏訪　彰］

沿革・産業

これらの島々は古くは伊豆国に属したが、近世には江戸幕府の直轄地となり、明治に入り所管が転々と変わったが、1876年（明治9）静岡県編入を経て、1878年東京府に編入された。また、中世から近世には伊豆七島は流刑地となり、近世には多くの流罪人が送り込まれ、島の社会に影響を与えた。現在、東京、熱海(あたみ)、下田(しもだ)から船便のほか、大島、八丈島へは羽田空港、大島、新島、三宅島、神津島へは調布飛行場からの航空便もあるが、一般には交通に恵まれていない。それが産業に影響し、古くから農林水産依存のみのところへ、離島という隔絶性が、つねに生産物の商品化を阻み困難なものにしてきた。大島の酪農、椿油(つばきあぶら)、新島の近世以来の伝統産業のくさや、八丈の名を生んだ古くは八丈絹とよばれた黄八丈(きはちじょう)など特産はあるが、生計を維持するほどのものには成長していない。しかし最近この地域は、火山景観の変化と、豊富な植物相、黒潮の海に臨む海岸美などの自然美に加えて、中世以来の歴史の跡が至る所にみられるなど、観光資源として価値が認められて、1964年（昭和39）富士箱根伊豆国立公園に編入され、数多くの観光客が訪れる所となっている。

［菊池万雄・諏訪　彰］

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