|Area||0.4 km2 (0.15 sq mi)|
|Length||1,500 m (4900 ft)|
|Width||550 m (1800 ft)|
|Highest elevation||210 m (690 ft)|
Udone-shima (鵜渡根島) is a volcanic, deserted island located in the Philippine Sea approximately 150 kilometres (93 mi) south of Tokyo in between Toshima and Nii-jima, in the northern portion of the Izu archipelago, Japan.
The island is the remnant of an andesite lava dome with sheer sides, the only visible portion of a submarine volcanic caldera. The above sea-level portion has a surface area of approximately 0.4 square kilometers, with a summit height of 210 metres (690 ft). The main island is surrounded by a number of rocks.
This island shares many similarities in its biodiversity in common with neighboring islands such as Nii-jima. Being surrounded by rough sea, vicinity to the island is rather difficult to visit in fact, and this made the natural environments of the islands and nearby atolls protected. Indo-Pacific bottlenose dolphins that newly inhabited around Udone-shima as their residential range has been expanded wider even onto Honshu coasts. Larger sharks inhabit the area. Historically, a breeding colony of now-extinct Japanese sea lions once existed on the island as well.
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