Prior to November 2013 , I think I can safely say that nearly no one knew about this particular island located in the Pacific ocean, about 1000 km south of Tokyo, the nearest islands are part of the Bonin group.
To give an idea of the remoteness of the place, it takes about 26 h by boat from Japan’s mainland to the nearest island.
Much better known due to an historical battle during WWII and an emblematic picture, Iwo Shima, to the south, is itself part of the aptly named volcano islands.
Prior to 1973, the islet was pretty calm as the latest eruption dated back to about 10 000 years. The submarine volcano had been mapped and the island is part of the northwest ridge of the caldera.
The submarine structure is about 3000 m high and 30 km wide at the base.
The eruption of 1973-74 lasted apparently from May ’73 to March ’74. A new island was created in the process, but it was partly destroyed by the elements later.
This is a map (from //www.gsj.jp/hazards/volcano/nishinoshima2013/) showing the bathymetry of the volcano and the location of the initial eruption.
Aoki et al made (La Mer, 22:248- 256) some analysis of rock samples in 1983, collected on and near the island. Their conclusion is that the lavas types are associated with Tholeïtic Basalts.
The present eruption began in November 2013 and was made public on the 20th. At first we saw some pictures and videos of a separate islet, showing the cypressoid jets which are characteristic of a shallow underwater eruption.
The eruption went on unabated and soon the new island merged with the older remnants of the ’73 eruption. This evolution is very well shown by this picture from the Japan Geographical Institute. See also: my video using the elevation data.
On this picture it is very clear that there was at first only one volcanic cone, but on the picture dated 16/02, a second edifice is visible.
There was also an IR picture taken showing the paths of the lavaflows. (Image dated 11/02/14)
Another set of pictures from
Considering the rate of lava extrustion I found some information on this site.
Apparently the rate of lava extrustion seems quite linear (or regular).
Note that apprently in Early January 2014 the island surface was equivalent to the 73-74 eruption
The lava extrustion rate seems to be in the range of 0,5 to 1 x 10⁵ m3 a day.
And the quantity of lava having reached the sea up to 9 January 2014
The latest news we have of the volcanic island date back to April 15 on the Japan coast guard site.
The main cone is still puffing happily away. In fact there are 2 active cones, one is more active than the other.
The lava flows are still reaching the ocean, as we can see some vapour rising from the waves on the left of the picture.
All in all the eruption seems to be continuing unabated. However, some sismological data is missing as there is apparently no seismometer installed on the island, we can only rely on the pictures, videos and satellite data.
About Modis data here is a small animation I made using the Modis thermal alert pictures. Do not pay attention to the date stamp at the bottom of the image, the video shows the different satellite images since April 1st ending today (21st April). There seems to be no active spot since the 18th, but as you will see, this happened also some times since the beginning of the month, so it is not possible to say if this corresponds to a pause or an end to the eruption, or if it is only due to cloud cover for instance.
About the Digital elevation data made available, here is a video which shows the terrain elevation for different dates and so shows the evolution of the volcano on 4 different dates. The last data is for 22/03. The elevation data comes from http://saigai.gsi.go.jp/2/20131120nishinoshima/nishinoshima_3d
Comments by dfm:
I have exagerated a bit the vertical component, but it is interesting to note that on the last part, the elevation of the new part of the island is clearly much higher than the old remnants of the ’73 eruption. This shows that the new island should stay above the water line for a while.
There is also this last video, which is the latest available from the JCG. It shows very well the 2 active cones and the lava flows getting to the sea on one side of the new island.
This eruption is really something very interesting as we can see a new island building itself. The follow up done by the different Japanese agencies is of high quality. The only point we may regret is the absence of monitoring equipment on site.