Sakurajima eruption

[bjdeming]

Nah, it's coming from that area -- I watched it re-form. Haven't seen fumaroles on the cam there before, but it does look like hot air is rising from various scattered points, with subsequent condensation of water vapor.

There's no oomph to it, though the appearance of convection is worrisome (if it wasn't a mistaken glimpse of the plume from the crater on the other side of that rock wall).

They just issued a routine report yesterday! (It's Tuesday there now.)

Well, they have Sakurajima wired in every possible way -- they've even tunneled into it to place instruments. No one is warning of an eruption or other trouble yet. We'll just have to see what happens next -- wish there was a public-facing thermal cam.

 

[bjdeming]

Its intensity seems to pulse up and down slowly and now seems on the wane. It could be some quirk of water circulation inside the mountain, combined perhaps with erosion.

That recent slow-moving Typhoon No. 10 made landfall nearby and the volcano's summit was wrapped in wind-driven clouds on cam for at least a couple of days.

 

[bjdeming]

That area apparently dried out, as the summit flank has been back to its normal appearance on cam from the following day on.

I did not see mention of it in the observatory's update through the 11th.

Sakurajima is having the occasional typical (though, again, more intense) vulcanian blast:



It does look quite apocalyptical on cam just now --

-- but that seems to be storm clouds, and 2 a.m. lighting, as far as I can tell.

 

[bjdeming]

No major changes -- still Level 3 and still doing more intense and ashier explosions than during its "soccer-game" period -- but Zaiho has a nice video of the 12/27 blast that also shows split-level meteorological cloud movements and just some darn pretty backscattering in the background as sunset approaches. (Camera D is a new feed and located somewhere on the north bay shore, perhaps Kirishima; the other three cams are in Kagoshima City.)



Today's update via Google Translate includes that eruption:

16:00, December 27, 2024 Fukuoka Regional Meteorological Observatory and Kagoshima Regional Meteorological Observatory

＜Warning around the crater (volcanic alert level 3, mountain entry restrictions) continues＞
　We would like to inform you of the activity status of Sakurajima from December 23rd to 15:00 on the 27th. There is a risk of an eruption accompanied by large volcanic blocks and small pyroclastic flows scattering more than 1 km from the Minami-dake summit crater and Showa crater.

Volcanic activity status​

　Active volcanic activity continues at Sakurajima.
　
　Two eruptions occurred at Minami-dake summit crater, both of which were explosions. In the explosion that occurred at 07:29 on the 23rd, smoke rose up to 3,400m above the crater rim, and large volcanic rocks scattered in a ballistic trajectory reached the 7th station (about 1,000m from Minami-dake summit crater). In addition, fire reflections were observed at the crater throughout the period at night using a high-sensitivity surveillance camera.
　
　No eruptions or fire reflections have been observed at Showa crater.
　
　Volcanic earthquakes have been few. No volcanic tremors have been observed.
　
　In a field survey conducted on the 24th, the amount of volcanic gas (sulfur dioxide) emitted was high at 2,000 tons per day (3,400 tons on the 17th).
　
　In a field survey conducted on the 25th, no particular changes were observed in the geothermal conditions on the southeast slope of Minami-dake or near Showa crater compared to previous observations. In addition, within Sakurajima, a glow from the Minami-dake summit crater was observed, barely visible to the naked eye.
　
　Continuous GNSS observations have confirmed slight shrinkage on the baseline within Sakurajima since around January 2024, which is thought to be due to mountain shrinkage. In addition, the baseline that sandwiches the Aira Caldera (inner Kagoshima Bay) has shown a gradual expansion indicating a long-term expansion deep underground in the Aira Caldera.
　
　In Sakurajima, magma has been accumulating deep underground in the Aira Caldera (inner Kagoshima Bay) for a long time, and the amount of volcanic gas (sulfur dioxide) emitted is generally high, so it is thought that eruptive activity will continue in the future. Please pay attention to future volcanic information...

Of note, and not to be sensational -- just to put Sakurajima in perspective -- Aira has had a supereruption in the distant past, so it's a supervolcano but nothing along those lines is looming in the near future and likely not during our lifetimes.

It's just doing what all restless calderas do and venting through Sakurajima on the south caldera rim now.

Sakurajima, as mentioned, is the real threat since it goes plinian every now and then, last in 1914.

 

[bjdeming]

Sakurajima flexed its muscles a little, roughly 24 hours ago:



Just a little. They didn't raise the alert level or issue a special statement on just one vulcanian event.

Things get bad when it's in the mood, which last happened in 1914 (PDF download of research paper).

Per JMA updates through the 17th, the volcano has been more explosive in terms of frequency, but not intensity, and instruments still measure shrinkage (while its daddy, Aira Caldera, continues with the long-term slow inflation).

 

[bjdeming]

This is getting to be a habit with Sakurajima but today's three-day update from JMA includes this explosion and the alert level is unchanged:



Just to review: Aira's expansion is where it was before the 1914 big Sakurajima eruption, which has everyone watching closely. What we don't want to see are flank fissures opening a la 1914.

 

[bjdeming]

NHK just did a story noting that Sakurajima has had 50 eruptions so far this year -- more than in all of 2024.

JMA's update reported 9 eruptions between March 31 and April 4, four of them explosive. They left the alert at Level 3.

And then, this today:



Tokyo VAAC reported ash up to 13,000 feet. It wasn't sustained, though, and JMA has not updated their page, at least not yet. Level 3 is still in effect, per that.

Again, the ground above Aira Caldera, on whose rim Sakurajima sits and from which it gets its magma, is at the same level it was just before the 1914 Taisho plinian eruption.

If Sakurajima were to blow now, I don't know if the summit would be the vent or if a set of fissures would open up on the east and west flanks, as in 1914.

At least the people are aware and they do drills and have a robust plan. Hope it's never needed.

 

[bjdeming]

Zaiho hasn't yet posted video of the April 5 blast but here is one on April 2 (when, I'm guessing, a dome blew up).

The larger ballistics, still incandescent, show up nicely in the twilight. This is one reason why there are exclusion zones on active volcanoes.

 

[bjdeming]

(From the blog just now)

Per today’s JMA update, Sakurajima had 12 eruptions, eight of which were explosions. Level 3 alert is maintained.

While this is all still relatively low intensity, it is a change in behavior from those long-gone days of vulcanian blasts now and then.

If those could be compared to a hand slapping a volleyball, this layperson sees it now as a clenching fist, with arm muscles tightening for a blow.

This explosion below, some ten hours ago, will count on the next update. Note that the plume, while impressive, does not have the power yet to completely ignore prevailing winds and rise vertically.

Yet.

 

[bjdeming]

X translation: "Sakurajima today" -- actually yesterday, given the time zones. Still, when it's quiet, it's beautiful.



BTW, that edifice is the result of two volcanoes that formed and then combined, their respective craters both being active for a while, although now it's just North Crater, Minami-dake, that's active.

A third, smaller crater, Showa, opened near Minamidake in the twentieth century and has had some lava flows and other activity but it has been quiet recently.

 

[bjdeming]

I've been expecting this -- Sakurajima has been quiet too long. It is plugged <layperson opinion> and is swelling.

Today’s update, via Google Translate — the alert level is unchanged, and if/when Sakurajima goes off, ashfall is expected mostly on the island (this channel has excellent livestreams):

Japan Meteorological Agency
Home > Information page for volcano climbers > Volcanic activity status
Status of volcanic activity (Sakurajima)
…
Municipalities subject to eruption warnings
In the following cities and towns, please be cautious and restrict access to the mountain around the crater.
Kagoshima Prefecture: Kagoshima City
Volcanic eruption warnings and forecasts
…
16:00, May 14, 2025 Fukuoka Regional Meteorological Observatory and Kagoshima Regional Meteorological Observatory
Crustal movements indicating mountain expansion are being observed on Sakurajima. There is a risk of an eruption accompanied by large volcanic blocks scattering over 1 km from the Minami-dake summit crater and Showa crater, as well as small pyroclastic flows. In addition, caution is required for ashfall on the downwind side.
Volcanic activity status
On Sakurajima, crustal movements indicating the expansion of the mountain have been observed using tiltmeters and extensometers installed on the island since around 8 p.m. on the 12th. There have been no eruptions, including very small ones, since May 5th. If an eruption occurs at the Minami-dake summit crater or Showa crater that relieves this mountain expansion all at once, it may be accompanied by a large amount of ashfall, mainly on Sakurajima Island. Please use the ashfall forecast issued by the Japan Meteorological Agency to find out the areas where ashfall and small volcanic rocks are expected to fall.
Disaster prevention precautions, etc.
Within approximately 2 km of the Minami-dake summit crater and Showa crater, be on guard for large volcanic blocks and pyroclastic flows that will be scattered in a ballistic trajectory due to the eruption. Be careful on the downwind side, as not only volcanic ash but also small volcanic blocks will be carried by the wind and fall far away.
Be careful as there is a risk of window glass breaking due to large air vibrations caused by the explosion. Please be aware that depending on the future ashfall situation, there is a possibility of debris flows occurring during rainfall.

 

[bjdeming]

​

Eruption #3 is ongoing. The column is relatively low and responding to prevailing winds -- not plinian, IOW -- and these winds are currently blowing the ash away from Kagoshima City, though other cities might get some -- the whole bay shore is urbanized.

Ashfall looks to be heavy on the island downwind of the summit. Pyroclastic flows, when they happen, are generally short here and have stayed within the exclusion zone for all recent activity.

Sakurajima had erupted three times by 11:00 a.m. on the 15th, with smoke rising to heights of over 1,000 meters each time.
According to the meteorological observatory, Sakurajima erupted at 7:08 a.m. on the 15th, with smoke rising to a height of 1,000 meters from the crater.
Further eruptions occurred at 10:14 and 10:45 a.m., with ash plumes rising to 1,100 m and 1,300 m, respectively.
The eruption, which began at 10:45 a.m., is still ongoing, and by 11:15 a.m. the smoke had risen to 1,700 m from the crater…
_ Source (autotranslated)

 

[bjdeming]

Zaiho cam A screenshot:

Zaiho cam B:

Zaiho cam C (the folks at Kagoshima U are zooming this in now and then):

and Zaiho cam D:

 

[bjdeming]

That is an impressive jet, but not driven by plinian-style MOMENTUM upwards. Air entrainment seems too weak at this point to totally overcome the winds.

One of the big unknowns in volcanology, from all sources I've read, is how eruptions do or don't escalate. There are so many factors, including what the initial stages of an explosive eruption might do to the conduit and vent, as well as whether or not gassy magma gets tapped.

<layperson speculation> Three eruptions in two hours is out of the usual for Sakurajima recently.

Gases and their bubbling out of solution are big troublemakers. Sakurajima is generally a fairly open-conduit volcano, so this stuff coming out now is well degassed. We'll just have to wait and see if Papa Aira feels like sending some new stuff up the line... </layperson speculation>

 

[bjdeming]

At the very least, it does not seem to be weakening. The ash volume is less, but the column is just as high and closer to vertical than it appeared before.

As far as I can tell, they haven't raised the alert from its longstanding 3 to 4 (the highest) (correction: it's a 5-point scale, not 4).. Here's JMA's six-hour ashfall map (Japanese, but animation).

BTW, you can see on the background graphic how Sakurajima is an island connected to the shore by a thin line: one of the 1914 lava flows. Kagoshima City is on the left side of the map.

Of note, Tokyo VAAC hasn't issued an advisory in three hours and counting. The ash is more voluminous than usual but at low altitudes.

 

[bjdeming]

It does seem to be winding down now. That third episode, since it lasted so long and produced so much ash, probably was the climax of this series.

It overall certainly was more than the expected one-shot "popped cork" blast that often happens with a plugged conduit. Wonder what Sakurajima and its daddy will do next -- probably go back to the routine of caldera expansion and vulcanian explosions, I guess.

 

[bjdeming]

X translation: "Before 6:30 PM, still billowing smoke"

By golly, it's still going on at around 9 p.m., local time! At a low level, though, and hard to see on the cams because of darkness..

JMA did a special update. Per Google Translate:

Volcanic activity status​

　An eruption has been occurring at the Minamidake summit crater since early this morning (15th), with smoke rising up to 3,000m above the crater rim. The mountain expansion that had been continuing since around 8pm on the 12th has been changing to a tendency for the mountain to shrink since around 11:30am on the 15th, but it remains in an expanded state compared to before 8pm on the 12th.
　
　If an eruption occurs at the Minamidake summit crater or Showa crater that causes this mountain expansion to disappear all at once, it may be accompanied by a large amount of ashfall, mainly on Sakurajima Island. Please use the ashfall forecast issued by the Japan Meteorological Agency to find out the areas where ashfall and small volcanic rocks are expected to fall.

Disaster prevention precautions, etc.​

　Within approximately 2 km of the Minami-dake summit crater and Showa crater, be on guard for large volcanic blocks and pyroclastic flows that will be scattered in a ballistic trajectory due to the eruption. Be careful on the downwind side, as not only volcanic ash but also small volcanic blocks will be carried by the wind and fall far away. Be careful as there is a risk of window glass breaking due to large air vibrations caused by the explosion. Please be aware that depending on the future ashfall situation, there is a possibility of debris flows occurring during rainfall.

 

[bjdeming]

From the blog, including today's JMA update via GT:

of time, and the amount of volcanic gas (sulfur dioxide) emitted is also generally high, so it is thought that eruptive activity will continue in the future. Please pay attention to future volcanic information.
The number of volcanic earthquakes and explosions is as follows. Note that the number of volcanic earthquakes is a preliminary figure and may be changed at a later date as a result of further investigation.

[Layperson speculation] That is an unusually low SO2 output for an erupting volcano. Combined with the expansion, I wonder if it means that a cap still exists somewhere in the plumbing. [/layperson speculation]

 

[bjdeming]

Sorry -- the JMA daily update didn't copy fully. Here's the whole thing:

16:15, May 16, 2025, Fukuoka Regional Meteorological Observatory and Kagoshima Regional Meteorological Observatory

<Warning around the crater (volcanic alert level 3, mountain entry restrictions) continues>

We would like to inform you of the activity status of Sakurajima from May 12th to 15:00 on the 16th. Sakurajima has been in a state of expansion. There is a risk of an eruption accompanied by large volcanic rocks and small pyroclastic flows that will fly more than 1 km from the Minami-dake summit crater and Showa crater. In addition, caution is required for ashfall on the downwind side.

Volcanic activity status

Active eruption activity continues on Sakurajima.

The mountain expansion that continued from around 20:00 on the 12th was temporarily contracted by the eruption from around 11:30 to around 15:30 yesterday, but it has resumed expansion and is continuing since then. There is a possibility of a large amount of ashfall in the future, mainly on Sakurajima Island. Please use the ashfall forecast issued by the Japan Meteorological Agency to check the areas where ashfall and small volcanic rocks are expected to fall.

There have been 10 eruptions and 7 explosions at the Minami-dake summit crater. The eruption that began at 10:45 yesterday (15th) continued until around 4:00 today (16th), with volcanic smoke rising up to 3,000m above the crater rim. Large volcanic rocks, which were scattered in a ballistic trajectory, reached as far as the 6th Station (approximately 1,200m from the Minami-dake summit crater). Eruptions have continued to occur intermittently since then.

There have been few volcanic earthquakes. Volcanic tremors have occurred, mainly associated with eruptions.

In field surveys conducted yesterday and today, large amounts of ashfall were confirmed, mainly on the eastern side of the island yesterday, and mainly on the northern side of the island today.

In a field survey conducted on the 12th, the amount of volcanic gas (sulfur dioxide) emitted was 300 tons per day (900 tons on the 2nd), which is somewhat low.

Continuous GNSS observations have shown a gradual expansion over a long period of time along the baseline that sandwiches the Aira Caldera (inner Kagoshima Bay), indicating a deep underground expansion of the Aira Caldera.

At Sakurajima, magma has been accumulating deep underground in the Aira Caldera (inner Kagoshima Bay) for a long period of time, and the amount of volcanic gas (sulfur dioxide) emitted is also generally high, so it is thought that eruptive activity will continue in the future. Please pay attention to future volcanic information.

The number of volcanic earthquakes and explosions is as follows. Note that the number of volcanic earthquakes is a preliminary figure and may be changed at a later date as a result of further investigation.

 

[bjdeming]

Sakurajima can't be seen clearly, what with night and rainy-season clouds, but it appears to still be erupting at that low intensity level. This is confirmed on the ash forecast page graphic.

Meanwhile, I found this geography case study on the volcano and the region.

This is just layperson speculation, but I think that the change in behavior, especially a change to increased eruptions (even though not to major levels yet), is worrisome in light of the magma source (Aira) being at the same level of inflation that it was at before the 1914 Taisho event.

Taking a more positive view, that 1914 eruption surprised everyone. There was no prior eruption sequence like this before the flank fissures opened up, east and west, and went plinian.

Those resulted from dikes, presumably ones that formed along lines of weakness as internal pressure increased -- that quiet volcano of January 1914 was a ticking bomb.

Now pressure is building but it's also being released via the summit crater Minamidake (Showa, the other crater, has been quiet for months).

Whatever balance there may be in this release might help keep things from escalating, but this layperson doesn't like the way Sakurajima stopped contracting while it was erupting and began expanding again -- while it was erupting.

That doesn't usually happen -- it's typically expand --> erupt --> contract, at explosive volcanoes, too, AFAIK as well as at mellower ones, say, in Hawaii and on the Reykjanes Peninsula in Iceland.

Could a packet of magma larger than what the current Sakurajima conduit can handle be trying to rise?

If so, maybe it would help if Showa opens up, too. It's also worth noting that there are seafloor vents around Sakurajima, too, and once (at least) a small submarine lava platform formed near the island!

Lots of ways this could go. Hopefully, it will just settle back down.

If escalation or a new vent comes, it likely will be preceded by earthquakes, and perhaps not small ones, either. None have been reported yet in this current round (in the past, some small swarms have occurred in the bay -- it's an active tectonic feature, the Kagoshima Graben, as well as a complex of calderas and volcanoes).

And if it opens underwater, there will be surtseyan activity (plus it will temporarily ruin the fishing resources).