Japanese volcanic islands merge.

Niijima, a new volcanic island that appeared in November 2013, has merged with the neighbouring island of Nishinoshima, another volcanic island which last erupted in 1973, according to NASA. When the new island initially appeared it was 500 m from Nishinoshima, and it was thought that it would probably be a short-lived structure, produced by a single bout of volcanism, then washed away over the following few years. But Niijima has now expanded and completely engulfed Ninioshima, and is apparently here to stay.

Satellite image of Nishinoshima and Niijima captured by NASA's Earth Observing 1 on 8 December 2013. Earth Observatory.

Satellite image of Nishinoshima and Niijima captured by NASA's Earth Observing 1 on 24 December 2013. Earth Observatory.

Image of the new, combined island taken on 30 March 2014. Earth Observatory.

Nishinoshima and Niijima lie on he boundary between the Pacific and Philippine Plates, where the Pacific Plate is passing beneath the Philippine Plate as it is subducted into the Earth. As the Pacific Plate is subducted it is melted by the heat and pressure of the planet's interior. The lighter fractions of this melted material then rise through the overlying Philippine  Plate as magma, fueling the volcanoes of the various islands and island groups that lie along the boundary.

The approximate position of the new island. Google Maps.

See also...

 Small eruption in the Aso Caldera, Japan.

 Magnitude 5.4 Earthquake in Ibaraki Prefecture, Japan.

 Volcano creates new island in the west Pacific.

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Volcano creates new island in the west Pacific.

A volcano has created a new island off the shore of Nishinoshima, a remote and uninhabited island Belonging to Japan, which is about 1000 km south of Tokyo and about 1600 km north of Guam. The island is about 200 m in diameter. It is unclear exactly when the island first appeared, but on Wednesday 20 November 2013 the Japan Coast Guard issued a warning about smoke and ash issuing from the new island (aircraft need to avoid volcanic ash as it melts in their engines, forming a glassy substance), and TV footage of an eruption on the island has subsequently emerged.

Steam issuing from the new volcanic island on Wednesday 21 November 2013. Japan Coast Guard.

Nishinishima lies on he boundary between the Pacific and Philippine Plates, where the Pacific Plate is passing beneath the Philippine Plate as it is subducted into the Earth. As the Pacific Plate is subducted it is melted by the heat and pressure of the planet's interior. The lighter fractions of this melted material then rise through the overlying Philippine  Plate as magma, fueling the volcanoes of the various islands and island groups that lie along the boundary.

The approximate location of the new island. Google Maps.

While the island can accurately be described as new, it is not evidence of a new volcano, rather a new vent on the side of the main Nishinishima volcano. It is unlikely to remain as a new island. Most probably the bulk of the material is poorly consolidated ash and cinders, which will be quickly eroded away. If the vent does start to produce more permanent rock-forming lava then this will be more resilient to erosion, but in this case the island is likely to grow and become attached to the Nishinishima mainland.

See also Tokyo shaken by Magnitude 5.4 Earthquake on the Bōsō Peninsula, Magnitude 6.8 Earthquake off the east coast of Japan, Eruption and pyroclastic flow on Sakurajima, Kyushu, Magnitude 5.8 Earthquake in Fukushima Prefecture, Japan and Magnitude 6.9 Earthquake in the Izu Islands to the south of Japan.

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