October 26, 2014, 2:06 p.m. Pacific: Sakura-Jima has had bursts since I wrote this article back in 2013, but today I saw news about a Kobe University study about caldera eruptions that mentions this caldera. The English-language headlines were dramatic, as one might expect, but I tracked down the original KU news report. It is in Japanese.
According to the Google-translated English version, the researchers – Yoshiyuki Tatsumi and Keiko Suzuki – studied Aira Caldera/Sakura-Jima as well as Kikai. That’s not a great translation, but I am assuming they studied the entire volcanic front in that region (which I haven’t written about yet, as it takes a lot of research, which I’m okay at, and basic geochemistry knowledge, which I’m not). I’m going to wait for the study to be published (hopefully in English) on November 11.
In the meantime, though, to counter the vaguely menacing headlines, it’s important to note that nobody is saying Aira, Kikai, or any other specific caldera is going to erupt in “the Big One” in the near future. If anything, as far as one can tell from the GT news release, it might be a surprise whenever any such supereruption occurs.
Anyway, per GT, the news release specifically says (and the news stories I read completely miss):
At the moment, it is not possible to identify huge caldera eruption would happen anywhere in the Japanese archipelago, but it is repeated eruptions of this class up to seven times in 120 000 years, crustal strain rate also think about the small central-southern Kyushu I considered, and it also appropriate from the viewpoint of assuming the worst.
Headline writers love it when researchers assume the worst-case scenario. Sigh. The study looks interesting, though. More on it in a separate post later, in November.
What a lot of beautiful activity at Sakura-Jima volcano in just one day last week!
The Bigger Picture
Volcano cam addicts know that there’s usually activity, some of it spectacular, at this Japanese volcano’s webcams (see bottom of post for links).
But it’s not so pretty when you consider that Sakura-Jima, one of the country’s most active volcanoes, is almost an urban park.
There’s plenty of water between the volcano and the cities, so it’s okay, right?
Well, the bay is only there because Sakura-Jima sits on the SSW edge of a much larger volcanic crater – the Aira Caldera – that had a huge (VEI 7) eruption some 22,000 years ago and collapsed in on itself.
That’s right – our spectacularly active volcano is just the new little kid in the neighborhood.
But wait – there’s more.
Aira is only one of several calderas that form a volcanic front in this part of the island of Kyushu.
What’s going on here?
Japan sits in a subduction zone.
In the area of Aira Caldera/Sakura-Jima, the Philippine Sea Plate is subducting under the continental plate that Kyushu island sits on, because of plate tectonics.
As the down-going plate moves into Earth’s hot interior, it melts. Some of that magma reaches the surface, where it erupts.
Since this is happening all along the edge of the plate, you get a volcanic arc (labeled “island arc” above).
People and the Volcano
You don’t read scare headlines about Aira Caldera/Sakura-Jima. People are too concerned about the very immediate hazards here to fool around with media sales tactics.
It’s a Decade Volcano and intensively monitored by organizations including Kyoto University’s Sakurajima Volcano Research Center, as well as the Japan Meteorological Agency which has the volcano at a level 3 alert right now because…well look at the video at the top of the page.
A local JMA station, the Kagoshima Local Meteorological Observatory (Japanese), keeps close watch on Sakura-Jima and works in conjunction with Kyoto University and other organizations.
JMA is also in charge of the Tokyo Volcanic Ash Advisory Center – check out their current advisory for Sakura-Jima. (Tokyo VAAC is part of a global network set up in the 1990s after incidents where jets had problems after flying into volcanic ash.)
Local emergency planners are also in the loop, as described in Kagoshima Prefecture’s Sakurajima Taisho Eruption 100th Anniversary Project website. I like this website – no scare headlines, just a simple statement:
We face Sakurajima and live in harmony with it
Each respective organization protects us
Human nature is beautiful, too., especially on a quiet sunny day.