Tori-shima

Tori-shima, Izu-shotō

The uninhabited island of Tori-shima (鳥島)is the southernmost island proper of the Izu Island chain. Only the Sōfu-iwa (Lot's Wife) pinnacle, 74 km distant, has a more southerly latitude. Tori-shima is located 220 km south-southeast from Aoga-shima and some 535 km southeast from the central east coast of Honshu; the northernmost islands of the Ogasawara-shotō (Bonin Islands) lie 355 km to the southeast.

The island of Tori-shima represents the only exposed portion of a far larger submarine volcanic structure known as the Tori-shima Seamount. Standing on the submerged southern rim of the seamount's 8 km wide summit caldera, Tori-shima is just one of several caldera rim volcanoes. In the vicinity are a number of conical and flat-topped knolls (such as Dai-ichi Higashi) as well as a central cone, some 5 km distant. The entire structure has a volume in the region of 466 km² — ranking it as the second largest volcano of the Izu-shotō after Miyake-jima.

Tori-shima island itself is a small, circular-shaped island of 4.8 km² in area with a diameter of 2.7 km and a circumference of 6 km. The eastern and western sides of the island are the outer walls of a caldera that rise steeply to a height of 387 m above sea level at Asahi-yama on the eastern rim and to 372 m at Tukiyo-yama on the western rim. The northern and southern sides of the caldera have collapsed, forming steep cliffs of up to 300 m in height (see photograph). The summit of the island contains a 1.5 km wide crater from which emerges two dome-like central cones: Io-yama (394 m) and Komochi-yama (361 m).

Recorded volcanic activity on Tori-shima includes the August 1902 eruption that killed all 125 inhabitants of the island as well as destroying the then central cone and forming the steep-sided crater on the north coast. Activity in 1939 created the new central cone of Io-yama. 1998 saw the formation of a pit crater and 2002 the formation of a new crater.

The landscape of Tori-shima consists mainly of bare lava slopes with thick layers of ash and exposed rock. Vegetation, gaining a foothold on this fresh volcanic landscape, occurs in patches all round the outer slopes of the island but is particularly evident on the shallower slopes of the island's western side. Commonly found species include shrubs such as the Roundleaf Chastetree (Vitex rotundifolia), Pacific Chrysanthemum (Chrysanthemum pacificum) and Japanese Black Pine (Pinus thunbergii).

Birds found on the island include the endangered Short-tailed Albatross (Phoebastria albatrus) — Tori-shima is only one of a few north Pacific islands where this species is known to breed — Japanese Murrelet (Synthliboramphus wumizusume) and Tristram's Storm-petrel (Oceanodroma tristrami). The only mammals on Tori-shima are introduced rats.

Synonyms: Tori-shima, Torishima, Izu-Tori-shima

image: ASTER volcano archive jpl/nasa

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