Nishinoshima (Ogasawara)

Nishinoshima

Nishinoshima in March 2015
Highest point
Elevation 137 m (449 ft)
Coordinates 27°14′49″N 140°52′28″E / 27.24694°N 140.87444°E / 27.24694; 140.87444Coordinates: 27°14′49″N 140°52′28″E / 27.24694°N 140.87444°E / 27.24694; 140.87444
Geography
Location Volcano Islands, Japan
Geology
Mountain type Caldera
Last eruption 2013 to 2015 [1]

Nishi-no-shima (西之島, "western island") is a volcanic island 940 km south of Tokyo,[2] that is part of the Volcano Islands arc. The island was enlarged in 1974 after fresh eruptions created a new section of the island. Another eruption that began in November 2013 further enlarged the island. Its maximum height was estimated at 110 meters on 27 December 2014.[3] It has also been known as Rosario Island.[4]

Morphology

Nishinoshima before 1973

Prior to 1974, Nishinoshima formed a small, green island which had no eruptions in the past 10,000 years. The island was merely the tip of an undersea volcano some 3,000 m (9,800 ft) in height and 30 km (19 mi) wide at the base.[5] Its main period of activity was from the Late Pleistocene to the Holocene.[6] The volcano takes the form of a caldera, with the original Nishinoshima and some nearby rocks forming part of the northwest ridge of a caldera about 1 km (0.6 mi) in diameter.[7] The island was originally about 650 m (710 yd) long and 200 m (220 yd) wide.[8] A 1911 survey determined the caldera was 107 m (351 ft) at its deepest.[5] The volcano has many large, submarine, satellite cones to the south, west and northeast. The southern cone rises to within 196 m (643 ft) of the surface, around 9 km (6 mi) SSE of Nishinoshima.[5]

Eruptions

Prior to 1973, no eruptions had ever been recorded at Nishinoshima.

1973–1974 Eruption

Nishinoshima in 1978

On 30 May 1973, the crew of a passing ship noted that, at around 11:00, white smoke rose east of the island to around 100 m (330 ft) in the air every few minutes. An aerial inspection the next day said that the eruption was taking place 400 m (440 yd) east of the island. A whirlpool was also seen. Yellow-green sea water and floating pumice were seen 5 km (3 mi) north of the site. Another crew discovered that two black rocks were rising from the sea.

In July, the eruption continued to erupt water fountains every few minutes with white smoke rising to 100 m above sea level. An aerial inspection on 14 September noted that a new island had formed above the submarine eruption site, the island formed a cinder cone around 40 m (130 ft) high and 120 m (130 yd) across. The new island had a 70 m (77 yd) diameter crater that frequently ejected cinders to a maximum height of 300 m (980 ft). White smoke rose to a height around 1,500 m (4,900 ft) high.

In November, a fissure eruption was noted on the new island with a chain of cinder cones running from southwest to northeast, the most recent cones were formed at the end of the chain, with the original cone being destroyed by the waves. The cones were erupting ash to a height of around 300 m (980 ft).

In December, the new island grew larger than "old" Nishinoshima. The island was 700 m (770 yd) long and 250 m (270 yd) wide; the new island had now developed a central crater that rose to a maximum height of 40 m (130 ft). The cone was continuing to eject ash and cinders to a height of 100 m (330 ft). A small craterlet on the new island was also emitting lava flows.

By February 1974, the new island had developed two cinder cones at the western end of the new island, but only the eastern cinder cone was erupting. Observations on 11 January noted that the active eastern cinder cone was emitting a lava flow.

In March, the new island was still erupting; by then, the island had five cinder cones; one cinder cone was erupting red hot lava. Lava flows were still erupting from the new island's flanks. On March 1, the five cinder cones were quiet, but a large lava flow may have still been effusing from the island's flanks. After that, the eruption ended; wave movements then joined the new and old islands.

2013–2015 eruption

New island on 8 December 2013

In November 2013, an eruption created a new, small island south-southeast off the shore of the volcano.[9][10][11][12] By December 2013, the island rose 20–25 m (66–82 ft) above sea level, with an area of 56,000 square meters (13.8 acres). The island was considered large enough to maintain a presence above sea level for at least several years.[13][14] By 20 December 2013, the island had grown fast enough that experts predicted that it would probably join up with Nishinoshima before the end of 2013, and cease to be a separate island.[15] On 26 December 2013, the Japanese Coast Guard confirmed that the two islands had joined.[16]

The island was not given an official name but was mentioned in Japanese reports as "new island": atarashii shima (新しい島) or shintō (新島).[17] Government officials said the island would be named "after it is stable and it is clear it will remain".[18] As the island has merged with Nishinoshima, "there is little possibility it will be named as a separate entity."[19]

The United States space agency, NASA, says two cones have formed around the main volcanic vents and stand more than 60 m (200 ft) above sea level.[20] The newer portion of the island is now larger than the original Nishinoshima landmass. The merged island is slightly more than 1 km (0.6 mi) across.

During July and August 2014, lava flow increased, causing the island to expand rapidly to the east. Between September and December, the lava flow increased further and headed north, almost completely overrunning the pre-existing island.[21] On 27 December 2014, Japanese authorities said the island had reached nearly 2.3 km2 (570 acres) in size and is estimated to rise to about 110 m (360 ft) above the sea level and that the volcano was still active.[3]

The eruption continued throughout the first half of 2015, and the island continued to expand. However, by August, the volcano ceased to erupt smoke and ash, but continued to emit lava.[22] As of September 16, 2015, the total area of the island had decreased slightly, but the fumarolic zone had expanded as "vigorous volcanic activity continued without significant change".[23]

References

  1. ↑ "Nishino-shima volcano (Japan): active lava flows towards the eastern shore". 19 January 2015. Retrieved 18 February 2015.
  2. ↑ Smithsonian Institution, Global Volcanism Program
  3. 1 2 http://www.bbc.com/news/world-asia-30610447
  4. ↑ Freeman, Otis W. (1951). Geography of the Pacific, pp. 229-235.
  5. 1 2 3 Nakano, Shun. "Kaitei chikei". Nishinoshima Kazan (in Japanese). Geological Survey of Japan. Retrieved 17 February 2014.
  6. ↑ "Nishinoshima". Geological Survey of Japan. Retrieved 17 February 2014.
  7. ↑ Nakano, Shun. "Gaiyō". Nishinoshima Kazan (in Japanese). Geological Survey of Japan. Retrieved 17 February 2014.
  8. ↑ "Nishinoshima". Chiezō mini. Asahi Shinbun. Retrieved 18 February 2014.
  9. ↑ "Volcano raises new island far south of Japan". Times of India. 21 November 2013. Retrieved 21 November 2013.
  10. ↑ "Volcano Eruption Creates New Island". International Business Times. 21 November 2013. Retrieved 22 November 2013. with pictures.
  11. ↑ "Volcanic Blast Forms New Island Near Japan". Universetoday.com. 2013-11-21. Retrieved 2014-04-06.
  12. ↑ Netburn, Deborah. "Is Niijima here to stay? New image of the newest island on Earth". latimes.com. Retrieved 2013-12-20.
  13. ↑ "New volcanic island off Japan still growing in ongoing eruptions". UPI.com. Retrieved 2013-12-20.
  14. ↑ "Japan's newly created island is actually growing". Salon.com. Retrieved 2013-12-20.
  15. ↑ 新島、年内につながる可能性　西之島まで百メートル切る. 47News (in Japanese). Retrieved 20 December 2013.
  16. ↑ 新島、西之島と一体化＝海保が確認. Jiji.com (in Japanese). Jiji Tsūshinsha. Retrieved 26 December 2013.
  17. ↑ "しんとう". Hokkaidō Shinbun. 12 January 2014. Retrieved 16 January 2014.
  18. ↑ "名もなき新島、どんな運命　残れば領海わずかに拡大？　小笠原諸島". Asashi Shimbun. 26 November 2013.
  19. ↑ "Lava flow connects new islet with Nishinoshima island". Asahi Shimbun. 26 December 2013. Retrieved 27 December 2013.
  20. ↑ Volcanic islands merge in Pacific Ocean BBC, 8 April 2014
  21. ↑ "Nishinoshima coastlines".
  22. ↑ "Volcanic activity".
  23. ↑ "⻄之島の火山活動の状況（９月１６日観測）" (PDF) (in Japanese). Japan Coast Guard. Retrieved 18 September 2015.

External links

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