Nishinoshima (Ogasawara)


Nishi-no-shima is a volcanic island located around south-southeast of Tokyo, that is part of the Volcano Islands arc. It has also been known as Rosario Island.
Originally the above-water part of the ridge of an underwater caldera, Nishinoshima 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 and attracted worldwide attention. A volcanic cone soon formed, raising to an estimated height of 142 m by July 2016. The eruptions ceased by November 2015, though emissions of volcanic gases continued for several months afterwards.
As of 2016, the island was about in size and evinces the return of various plants and animal species.
There were further eruptions in 2017, 2018 and 2019, with the latest eruption continuing as of July 2020. This increased the island size to as of 2019.

Etymology

The island was named "Jena Island" when it was discovered by the Spanish ship Rosario in 1702. That was the island's name until 1904 when the Japanese term "Nishinoshima" was made the official name.
When a new island was formed in the 1973 eruption, that was called Nishinoshima Shintō, but due to erosion and shifting sands, that island joined the main island and ceased to be considered a separate entity.
During the early stages of the 2013 eruption, a new volcanic island was formed about southeast from the original Nishinoshima. The island was not given an official name but was mentioned in Japanese reports as "new island": atarashii shima or shintō. Government officials said the island would be named "after it is stable and it is clear it will remain". As the island has now merged with Nishinoshima, "there is little possibility it will be named as a separate entity."

Geology

Morphology

Prior to 1974, Nishinoshima was 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 in height and wide at the base. Its main period of activity was from the Late Pleistocene to the Holocene. 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 in diameter. The island was originally about long and wide. A 1911 survey determined the caldera was at its deepest. The volcano has many large, submarine, satellite cones to the south, west and northeast. The southern cone rises to within of the surface, around SSE of Nishinoshima.

1973–1974 Eruption

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 in the air every few minutes. An aerial inspection the next day said that the eruption was taking place east of the island. A whirlpool was also seen. Yellow-green sea water and floating pumice were seen 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 high and across. The new island had a diameter crater that frequently ejected cinders to a maximum height of. White smoke rose to a height around 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.
In December, the new island grew larger than "old" Nishinoshima. The island was long and wide; the new island had now developed a central crater that rose to a maximum height of. The cone was continuing to eject ash and cinders to a height of. 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 1 March, 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

In November 2013, an eruption created a new, small island south-southeast off the shore of the original island. By December 2013, the island rose above sea level, with an area of 56,000 square meters. The island was considered large enough to maintain a presence above sea level for at least several years. 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. On 26 December 2013, the Japanese Coast Guard confirmed that the two islands had joined.
The United States space agency, NASA, says two cones have formed around the main volcanic vents and stand more than above sea level. The newer portion of the island is now larger than the original Nishinoshima landmass. The merged island is slightly more than 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, leaving only a small portion of the old island exposed. On 27 December 2014, Japanese authorities said the island had reached nearly in size and is estimated to have risen to about above the sea level and that the volcano was still active. A pyroclastic cone formed around the vents which further rose the island to about 135 m by 23 February 2015.
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. As of 16 September 2015, the total area of the island had decreased slightly, but the fumarolic zone had expanded as "vigorous volcanic activity continued without significant change". Eruptions resumed soon thereafter, but 17 November 2015, was the date of the last observed explosive eruption. Fumarolic activity continued, but decreased in amount as no new lava flows were observed. Decreases in temperatures were also recorded, and subsidence was observed near the summit of the volcano. In August 2016, the Japan Meteorological Agency announced that the alert level for the volcano had been lowered, and that the no-entry zone had been reduced from a radius of to a radius of. This would finally enable landings on the island. Water discoloration was still evident immediately offshore in August, indicating that volcanic activity, while in significant decline, was still present. On 14 February 2017, the Japan Meteorological Agency cancelled all alerts for the island, declaring that there was no indication of subsequent eruptions.
On October 2016, a team of scientists visited Nishinoshima to conduct research on the island. Apart from documenting the island's ecology and geology, monitoring equipment was also installed for future volcanic activity.
Wyss Yim, a retired professor of Earth Sciences, has theorised that the Nishinoshima eruption caused the North Pacific Blob, a mass of warm surficial water off the Pacific Coast of North America.

2017 and 2018 eruptions

On 20 April 2017, the Japan Coast Guard confirmed explosive eruptions at the No. 7 crater at Nishinoshima and lava flows emerging from the base of volcano. Satellite imagery from 19 April also confirmed high temperatures on the island. Examination of the data revealed that the eruption likely began on 17 April. By 27 April, two lava flows had reached the sea, one on the west shore, the other on the south-west shore of the island. By 29 June, the flows had created two lobes, one extending 330 meters beyond the western shore, and other 310 to the south-west. The area of the island increased to. By July, surface temperatures began to decrease until they became indistinguishable from the surroundings in August; lava flows also stopped by the end of August. On 3 October, the Coordinating Committee for Prediction of Volcanic Eruptions of the Japan Meteorological Agency announced that Nishinoshima had likely ceased erupting. In June 2018, the JMA announced that the no-entry zone had been reduced from a radius of to a radius of. Within a month, however, the zone was returned to 1500m after small eruptions were spotted on 12 July 2018. These eruptions quickly subsided, and the no-entry zone was reduced to 500m on 31 October 2018.

2019-2020 eruption

On 6 December 2019, the Japan Coast Guard confirmed explosive activity in Nishinoshima has returned, with new lava flows entering the sea by the following day. The conditions were enough that the Meteorological Agency issued a warning to passing ships to stay clear of Nishinoshima..
In January 2020, the Japan Coast Guard observations confirmed that lava was flowing out on the northeast coast. Further activity was observed on 4 February, and the northern extension of the island was expected.
As of 25 June 2020, the explosive-effusive eruption was still continuing, with lava flows on the northeastern slope of the volcano, as well as ash plumes reaching 2600 meters.
On 4 July, an ash plume reached 8300 meters in height.

Ecology

Since the 2013 eruption, biologists have expressed great interest in how Nishinoshima would be colonized by plants and wildlife. It is expected that organic matter, mainly deposited by nesting birds in the form of feathers or excrement, would enrich the island surface for plants to grow. To prevent interference of the colonization process, researchers were also advised not to bring external species to Nishinoshima.
On October 2016, a team of scientists visited Nishinoshima to examine its environment and geologic makeup for the first time up-close. Their studies have discovered that both plant and animal life continue to exist on the remaining part of the old Nishinoshima island that had not been covered by lava. An accompanying video crew from Nippon TV captured masked boobies laying eggs and a pod of dolphins swimming off the coast. Gannets, bramblings and earwigs were also discovered living on the island by researchers. Several cetaceans have been known to live around the island prior to the eruption such as spinner dolphins and short-finned pilot whales, and above mentioned bottlenose dolphin. Humpback whales had been seen before the eruption, and their recent returns have been confirmed as well.
In terms of flora, plants that were present on the original island like goosegrass and purslane were found to be growing again on the "old" section of Nishinoshima.