Repost: Kirishimayama Volcano Group


Here’s a slightly revised post from 2018 about a complex set of Japanese volcanoes! Fortunately, they have been quiet now for over a year.
 

For most of us, the words “Japan” and “volcano” summon up an image of Mt. Fuji, near Tokyo. But this country has many more volcanoes, some of them not as simple in appearance as Fuji-san.

Take Mount Kirishima, for instance. It is a study in contrasts.

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Not least because it rises out of townlands and has a lot of vents. (Jun Seita, CC BY 2.0)

On the one hand, Kirishima frequently erupts; on the other, it’s a great place for a walk through the park.

The park

Here is someone’s video of a walk up three volcanoes in the area; the first two–Takachiho (crowned with a legendary spear, per Wikipedia) and Karakuni–are part of the Kirishima center; the last one, beautiful Kaimon, belongs to the Ata caldera underneath Kagoshima Bay.

That certainly looks peaceful. Volcanoes sculpt some of the most beautiful landscapes in the world.

But as you can see, a lot of people live near Mount Kirishima — a frequently active volcanic center.

A violent history

Starting some 600,000 years ago, huge caldera-forming eruptions began here, at the head of Kagoshima Bay on the island of Kyushu. Ever since then, volcanic events have been explosive in nature (not showing much runny “Hawaiian-style” lava).

About 330,000 years ago the style changed to building stratovolcanoes instead of big holes in the ground (which is what a caldera is, basically). Ever since, this complex volcano has built more than 25 relatively small peaks and cones. Two vents have been active recently: Shinmoedake and Ioyama.



This 2018 gives basic information for the Ioyama (or Mount Io) eruption. Both of these volcanoes have kept a fairly low profile since their 2018 activity. (Of note, Moto-Shirane volcano is not part of the Kirishimayama group; the nearby violent eruption referred to in this video was that of Shinmoedake.)


Although this hasn’t happened recently, magma occasionally interacts with ground water in the Kirishima volcanic group, forming a maar with the resulting steam-driven eruption.

This volcanic group is slowly becoming more active and its magma rate is increasing. Volcanologists are watching Kirishimayama closely to better understand how it works so they can most accurately predict its future course.

It’s not easy for an English-speaking layperson to understand Japan’s volcano monitoring system, but I have found online a web page for the Kirishima Volcano Observatory.

Also, the current Japan Meteorological Agency alert page in English (yes, JMA monitors geological hazards, too) does not list any Kirishimayama group volcanoes.


Featured image: NASA Earth Observatory.



Sources:

Global Volcanism Program. 2018. Kirishimayama.

Nagaoka, S., & Okuno, M. 2011. Tephrochronology and eruptive history of Kirishima volcano in southern Japan. Quaternary International, 246(1-2): 260-269.


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