Japan just got a little larger. Well, maybe. The ‘birth’ of a new volcanic island off among the chain of the Ogasawara (also known as the Bonin) Islands, around 600 miles south of Tokyo in the western Pacific, has caused a flurry of interest in the news media as video footage of the dramatic eruption makes the rounds. At 200 meters in diameter the new arrival has certainly made its presence felt – it burst into the world with a column of ash and steam rising to around 600m.
So far the new island remains unnamed. That’s a wise precaution because such islands don’t necessarily have a lot of staying power – if the eruption falters then the chances are that the newly-erupted material will erode fairly quickly. If the volume of erupted material continues to accumulate, however, the Bonin Islands could find themselves with a new companion – and the Pacific’s notorious Ring of Fire will have another active volcano.
The Birth of a Volcanic Island: How and Where?
Logic tells even the non-geologist that land has to come from somewhere – and volcanic islands are its primary source. At depth, the Earth is molten and, being relatively buoyant, this melted rock (magma) rises up to the surface, where it erupts in the form of volcanoes. Most of this production of ‘new’ crust is the result of plate tectonics and occurs at or in association with plate margins – either as submarine eruptions along ocean ridges, or as a result of subduction of one plate below another.
The new island is typical of the latter. The Bonin Islands are the product of the subduction of the westward-moving Pacific plate beneath the Philippine plate. The crust of the Pacific plate is forced downwards and melts under pressure at depth: the molten rock then rises and forms a line of volcanoes behind the subduction zone itself. When this process takes place under water, a volcanic island is formed.
Such eruptions are characteristically explosive. The coming together of (relatively) cold water and molten rock produces large quantities of steam and ash – a type of activity termed ‘surtseyan’ which calms once the volcano builds up to above sea level and the amount of water reaching the magma vent is reduced. The nature of the eruption then changes to become effusive rather than explassive – in other words, a gentler flow of lava typified by volcanoes such as Mauna Loa.
Such islands are common in subduction zones and volcanic island arcs are plentiful in the northern and western Pacific and elsewhere. Examples such as the Aleutian and Kuril islands are classic volcanic chains which, over time, mature to more substantial areas of land such as Japan and Sumatra – and eventually evolve into continents.
Other Volcanic Islands
The eruption of Japan’s newest territory (if such it remains) is, then, remarkable and possibly permanent but by no means unique. New islands appear all over the world; volcanologists Peter Francis and Clive Oppenheimer describe a number of other examples, one of which, in 1952, claimed a Japanese research vessel and the lives of her 31 crew. And the eruption of Krakatoa in 1883, which destroyed the original island, left a gap which is currently being filled by the growth of a new volcano named Anak Krakatoa – ‘son of Krakatoa’.
Submarine volcanism is not restricted to subduction zones and island arcs: new islands may also be formed as a result of the anomalous (and not fully understood) rise of large plumes of magma which may reach the surface away from the edges of tectonic plates. Where this occurs underwater, new islands are formed in a similar way. Perhaps the most famous example, and that which gave its name to the eruption style, is the Icelandic volcano of Surtsey, which appeared out of the sea in 1963 and is still going strong.
New Land: Sovereignty Complications of Appearing Islands
The consequences of new land go beyond the geological and into the realm of the geopolitical. Francis and Oppenheim describe how, in similar circumstances, the appearance of a new island in the Mediterranean led to a scramble to claim sovereignty among the states of Britain, Spain and Sicily. Alas – the new island did not survive long enough for the dispute to be resolved. Whether the eruption of Japan’s new baby “could cement Japanese sovereignty in regional dispute with China” as some news sources suggest, or whether it dips once again below the waves, remains to be seen.
Francis, P. and Oppenheimer, C. Volcanoes. (2004). Oxford University Press.
Guardian online. Volcanic eruption creates new land off coast of Japan. (2013). Accessed November 22, 2013.
Volcano Discovery. Nishino-shima volcano news and activity updates. Accessed November 22, 2013.