Some volcanoes deserve attention just because they are wonderful caramels that never stop tasting good. Nishinoshima is such a candy and I should really have written quite a lot more about her. In reality though it is hard to write about her since she does not have any monitoring equipment, nor does she have ready access for scientists to study her.
Still she is a wonderfully tasting caramel of scientific surprises and every week I find myself drooling over the brief reports from the Japanese Coast Guard and professor Nogami at the Tokyo Institute of Technology.
Nishinoshima is a very large mainly sub-aquatic volcano with a 9 by 11 kilometers caldera. The large seamount is mainly formed from hypersthene-augite-andesite with a density of 2.62kg per cubic decimeter.
The seamount and the caldera on top have several active volcanic peaks with the next tallest reaching to a height of 214 meters below the surface. It is believed that this volcanic vent has had several eruptions during the last century and that it might reach the surface sometime the next century.
The tallest volcanic went is of course the Nishinoshima Island. The island has appeared and disappeared several times due to the harsh conditions caused by the tall pacific waves. The island that was already above the surface during the start of the 1973 eruption had most likely formed during an eruption a few decades earlier. This “old” Island has by now mostly disappeared below the surface (except for a few small rocks).
The 1973-74 eruption lasted for approximately 9 months and doubled the size of the island. It formed five cinder cones that by now have been almost totally eradicated by the environment.
The current eruption quickly moved from a Surtseyan type of eruption into a mainly effusive phase where it has erupted large amounts of magma. Rapidly the new island joined the new Island and a new name was not needed, even though Nijima had been suggested as a possible new name.
It quickly became clear that the latest eruption was larger than the 1973-74 eruption. So far it has yielded 0.475 square kilometers of new landmass and covers about 0.9 square kilometers at the foot of the eruption. Averaging the depth given by the naval chart the eruption has so far ejected close to 0.2 cubic kilometers of lava.
For comparison the eruption at El Hierro that started at slightly greater depth never got closer than 100 meters from the surface.
As the eruption evolved it went through several stages and has so far given us such candies as shield volcano construction, lava streams from radial vents, two cone constructions, one of the cones constructed a radial fissure that surrounded it as the cone started to sink down, and now it is sprouting what looks like diminutive little stratovolcanic cone. Nishinoshima is really a candy that just gives new wonderful flavors in every weekly update.
Currently there are two active cones. The larger is ejecting burst after burst of fresh lava that rapidly is building up the steep sided cone in what looks like a proto stratovolcano. Around it a ring-fault has formed that is also actively venting lava-flows. The second smaller cone is having a diminutive lava lake and is emitting smoke and ash together with streams of lava. And to top it off there are fissures in the newly formed land that is actively emitting lava all over. From the looks of it the eruption is larger now than it was in the beginning.
So far the eruption has caused no great concern, but the Japanese Coast Guard has issued warnings for the maritime traffic. According to Nogami there is a slight risk that the eruption could turn explosive if the volcano is destabilized due to the high volcanic activity.
I guess that the reasoning behind that is that the volcano should have a fairly shallow magma reservoir and if that breaks the ocean could reach it quickly. Personally I am wondering if the currently active part of Nishinoshima is not connected to a larger reservoir that is located at depth inside the large caldera. If so it is rather unlikely that an eruption of this size could cause a magma reservoir collapse. Without instrumental evidence it is though impossible to say what is going on in this large brooding volcanic caldera.
I will be following this volcano intently since it is such a tasty treat.