Sakurajima eruption

[bjdeming]

Alert level: 3

• Latest official status update (autotranslated)
• Tokyo VAAC
• Japan Meteorological Agency (JMA) Sakurajima portal
• Kagoshima City home page (Japanese)

Per my note in the volcano thread, this appears (to this layperson) to be a possibly significant change in behavior towards more eruptions (still apparently low level).

Before the volcano began to deform (noted by JMA on the 22nd), it had an impressive but relatively tiny eruption on the 19th (and more on the three previous days that I didn't post in the volcano thread, though you can watch them at the Zaiho YouTube feed).

Before that, Sakurajima steamed away for months -- quite impressive and very reassuring because it meant that the vent was open and pressure likely would not build up.

Volcanoes are changeful places, though, and it seems to this layperson that something has changed.

If this were out in the boonies somewhere -- say, Klyuchevskoy in Kamatchka, which is really going to town this week -- I'd be tempted to do amateur speculation but absolutely not with Sakurajima.

Too much and too many lives are at stake in such a setting for amateurs to muddy things up. Local volcanologists and local officials will always be the ones to listen to in any volcano emergency.

And, hopefully, S. will just clear out a backlog of some sort at these same very low levels and then go back to "full steam ahead" mode.

As of right now, the most recent JMA update is the October 24th one, excerpted in the volcano thread.

 

[bjdeming]

Dawn is coming on, and yeah, looks like more of the same of the activity last evening.

People are active, too -- not something I've noticed at 5 a.m. before; boats are lit up, there are searchlights on a few and these keep shifting, and the lower lefthand part of the island is much more brightly lit than I recall seeing it before. No signs of mass movement over there, though (no lines of headlights).

Technically, it's been a peninsula since a 1914 lava flow connected the island to land, and I think there is a road over the causeway.

Something is going on across the bay on this side, though.

Lighter sky, can see the plume better; low, and not enough pressure to overcome winds. Good, but it keeps erupting...

 

[bjdeming]

Well, maybe some (from the blog):

<LAYPERSON SPECULATION>It's not surprising that there is so much water vapor from this volcano sitting out in Kagoshima Bay.

The question is, what is heating so much water right now? Obviously, magma is down there -- and lots of it, per JMA a year or more ago -- but are we seeing these emissions now because the magma is rising? Remember, the edifice inflation stopped and was totally compensated for by that lightning-show eruption the other night, per JMA.



Or is the plumbing system just readjusting after a major pressure release? And if so, will it set off the sort of self-feeding process of rapid magma rise that can (but doesn't always) trigger a magmatic eruption?

One of the biggest unknowns in volcanology, I understand, is what moves a volcano's plumbing past the point where eruption becomes inevitable.

Sakurajima doesn't seem to have reached that point yet (things tend to happen quickly once it's passed).

Technology and experience can show volcanologists a lot, but maybe we're all just waiting on the volcano right now.

As usual.

</LAYPERSON SPECULATION>

 

[bjdeming]

Today has gone well; most of the day thus far has just involved production of low-level ash punctuated by a big blast a few hours ago that rampaged a while. Now the white condensation clouds are back, but none of that instability seen yesterday.

That ashing/boom pattern today reminds me of Popocatepetl's routine; haven't seen it at Sakurajima before, but if the parallel is accurate, it could mean good news:

• Lava is erupting steadily, at low energy, through an open conduit (like Popo's). This would be good, if true.
• Construction of a lava dome. I haven't ever seen one mentioned by JMA, but don't see offhand why S. couldn't grow one (layperson opinion). There was a brief shower of bombs and spectacular impacts in the crater rim ash during this afternoon's explosion (C cam) that made me think of it; also this is what Popocatepetl does when it's ashing (and then the domes explode).

Well, if JMA does a new update, it will be out in about an hour. We'll see what they say.

Meanwhile, for any geonerds, I found this online version of the Sakurajima chapter of the Japanese Quaternary volcanoes series (it's in English).

 

[bjdeming]

JMA reports that the volcano is inflating again. The current update has almost the exact same wording as last time.

After that last series of eruptions, as noted, Sakurajima seemed to go through what I would call a dome-building/destruction phase if it were Popocatépetl. Then it had that explosion, followed by a return to the condensation-cloud phase.

It was so quiet now that this layperson figured the superficial plumbing system had stabilized and we were good to go, so to speak, for a while.

I haven't been watching it constantly lately and so can't describe changes step by step, but this morning on the cam in early light it looks like S. has that hydrothermal "fuming" look again.

Looks like we might see a repeat of the last episode.

And to this layperson, it does look more and more as though Sakurajima is building up to another 1914-style event. This is not at all the typical pattern I've seen over the last few years.

It might not come this round, or the next, or the one after that, and so on, but it's coming.

Japanese volcanologists make no bones about it.

And an impending "big one" is good to talk about (before it gets here) in the lay world, too, because volcanoes are so complex and we laypeople just see them in terms of disaster (the opening to Dante's Peak pretty much sums it up).

Anyone living near or likely to travel near an active volcano on alert needs to see more than that. We need to know how uncertain everything is, constantly, around these Earth-style pressure cookers in a shaky tectonic zone (usually), with the burner on High.

It's not at all a case of "let the observatory tell us what to do." It involves having individual, family, and neighborhood awareness and a plan, as well as knowing that authorities -- at best -- can only advise: in an emergency, you're on your own. Prepare accordingly (while continuing to normally and sociably lead the life you intend to protect).

Actually, that's good for any kind of hazard prep, of course (and not at all new to anyone in Dixie Alley!).

The Japanese, from the little I've read, are quite good at this. They will weather a major volcanic crisis as well as anyone could expect.

Those of us outside can only wish them well, and watch, and learn.

And look into whether any local volcanoes need watching, as we plan our next vacation or business trip.

Sigh. Sakurajima used to be just fun. The first part of this video -- if you overlook all the immature cussing and F-bombs -- shows that (and, more importantly, it shows us a better view of the volcano's human surroundings: "Sakurajima" means "Cherry Blossom Island.")

 

[bjdeming]

Japanese public broadcasting (NHK) doesn't like embedding, but here is their look at Kagoshima.

 

[bjdeming]

Per JMA update today:

Status of volcanic activity​

　At Sakurajima, crustal movements indicating the expansion of the mountain body were observed from around 00:00 yesterday (26th) using inclinometers and extensometers installed on the island. However, due to the intermittent occurrence of very small eruptions, it began to contract slowly from around 2:00 pm yesterday, and it appears that the expansion has now largely stopped.

Unspoken: "for now." Still, yay!

 

[bjdeming]

Didn't have a chance to read the whole October 27 update until now because I'd fallen behind a bit on an ongoing writing project.

There's a lot of other information in it besides that initial good news, and it also hints at the extensive monitoring work that goes on there right now:

Status of volcanic activity​

　At Sakurajima, crustal movements indicating the expansion of the mountain body were observed from around 00:00 yesterday (26th) using inclinometers and extensometers installed on the island. However, due to the intermittent occurrence of very small eruptions, it began to contract slowly from around 2:00 pm yesterday, and it appears that the expansion has now largely stopped.
　
　Active eruption activity continues at Sakurajima.
　Three eruptions occurred at the Minamidake summit crater. During the eruption at 3:46 on the 24th, volcanic smoke rose to 3,400 meters above the crater rim. The large volcanic blocks scattering in a trajectory reached as far as the 6th station (approximately 1200m from the Minamidake summit crater). In addition, fire reflections were observed at the same crater at night using a highly sensitive surveillance camera throughout the period.
　
　No eruption or fire eruption has been observed at the Showa crater.
　
　The number of volcanic earthquakes has remained low. Volcanic tremors mainly occurred in conjunction with eruptions.
　
　A field survey conducted on Sakurajima Island on the 24th confirmed a large amount of ash falling in Kurokami Town, which is believed to have been caused by the eruption that continued from 3:46 to 4:30 on the 24th.
　
　A field survey conducted on the 25th revealed that the amount of volcanic gas (sulfur dioxide) released was as high as 2,200 tons per day (previously on the 16th, it was 4,200 tons).
　
　An aerial observation conducted on the 25th with the cooperation of the Japan Air Self-Defense Force Air Rescue Team Kasuga Helicopter Airlift Team revealed that the crater on the north side of the Showa Crater had expanded slightly compared to the previous observation (March 8, 2023). I confirmed that it is. At the Minamidake summit crater, a high-temperature geothermal area was confirmed at the crater floor. Additionally, no particular changes were observed in the conditions around both craters.
　
　Continuous GNSS observations have shown that some baselines within Sakurajima Island have been slightly elongated since around January 2023, likely due to the expansion of the mountain, but this has been stagnant since around April. Additionally, along the baseline that spans the Aira Caldera (inner part of Kagoshima Bay), gradual elongation has been observed over a long period of time, indicating expansion of the deep underground of the Aira Caldera.
　
　At Sakurajima, magma has accumulated deep underground in the Aira caldera (inner part of Kagoshima Bay) for a long time, and the amount of volcanic gas (sulfur dioxide) released is generally large, so the Minamidake summit crater and the Showa crater Eruptive activity is expected to continue in the future. Please pay attention to future volcano information.

We will, we will.

 

[bjdeming]

JMA today (rest of update text is the same gist as in previous ones during edifice inflation times):

Status of volcanic activity​

　On Sakurajima, crustal movements indicating expansion of the mountain body have been observed since around 01:00 today (28th) using inclinometers and extensometers installed on the island.

 

[bjdeming]

Also, for geonerds, I found out that Sakurajima is quite different from Popocatépetl.

This abstract (jargon alert) of a well-cited paper offers one suggestion of how Sakurajima's 20th-century eruptions might have worked (including the 1914 eruption that S. is probably is building towards a repeat of in the future at some point):

Don't let the mention of Aira Caldera worry you overmuch; it's sort of like Campi Flegrei in that it's farther down, and if trouble was brewing of the sort that Aira has wreaked in the past, precursors would presumably be correspondingly huge.

That said, there is another smaller caldera just northeast of Sakurajima, under the bay, that is considered active (but is unmentioned in updates by the boffins who are most certainly monitoring it).

Also, some eruptions at Sakurajima have been submarine, but that is rare AFAIK.

Volcanic uncertainty: sigh.

 

[bjdeming]

It had a pop to 7,000 feet about four hours ago, per Tokyo VAAC -- small -- and the plume looks quite nice currently in moonlight, but that was vulcanian, this layperson suspects -- like it has been doing since the 1950s but on steroids.

Yesterday (the 29th in Japan), JMA reported that the inflation had dropped a little but the edifice was still expanded.

The main thing is that this is summit activity -- that conduit is still open. <Layperson speculation> This is good, so long as it's open enough to relieve pressure that otherwise might open up dikes that could reach the flank surface; wide enough opening seems to be the case, but the constant emissions must result in some plugging with degassed magma. The conduit into Minamidake is about 200 m wide, per the paper; Showa, which opened in 1939, is much smaller, but M. seems to be the important vent, at least historically.

I suppose pressure release might also depend on how much new magma might rise, and at how fast a rate, as well as how gassy the new stuff might be. </layperson speculation>

Anyway, Tokyo VAAC doesn't seem likely to issue new advisories yet, so we shall see.

 

[bjdeming]

Sakurajima is putting on a nice show. Tokyo VAAC lists the plume at only 9,000 feet.

 

[bjdeming]

There is more ashfall apparent in this one, but the plume looks to be mostly water vapor (white).

I lucked into being at the C cam when the initial ash blasts started and they were quite impressive, though I didn't see bombs this time. Also I thought I saw a little bluish fume (SO2) way off the right and downslope a bit, but it was only two brief impressions out of the corner of my eye and might not be valid.

Given that the plume is now lower (A cam), this layperson thinks that it is probably a series of vulcanian explosions -- thus far. Will keep an eye on it.

Layperson guess: in the last half-hour or so, it went from #3 to #4 or #5 on Dr. Iguchi's (PDF download) Figure 14:

(Dr. I. is actually describing something broader in long-term behavior, but I like the diagram for showing the closed conduit (3) to open (4 and 5).)​

This is still routine for Sakurajima in the sense of it being vulcanian (layperson opinion), and low level, but the behavior is still intensified compared to the good old background-to-a-soccer-game days, and probably progressing some, if that ashfall visible on the cams is significant.

The series of blasts right now is worth watching, too.

 

[bjdeming]

There certainly still seems to be an ash source right center on Cam C, but explosions don't propel it nearly as high as at first, let alone possess the oomph to sustain a 9,000-foot column.

This layperson's guess is that a lava dome blew and now more lava is extruding onto the crater floor, mostly degassed already.

Perhaps as it domes up enough to block the water vapor leak -- which is quite a big one and was even earlier today -- there's an explosion and Little Mr. Lava has to start all over again?

 

[bjdeming]

JMA hasn't updated their bulletin today, after reporting in the last one that the inflation recovered after a series of small blasts.

Sakurajima thus far has had one more blast since yesterday's, up to 10,000 feet per Tokyo VAAC. Judging from its current strong fuming, it will probably have another one today.

That lightning-show eruption was extraordinary, but <layperson opinion> summit activity at the level we saw yesterday is probably going to continue off and on. If and when S. is ready to go plinian it will happen out of fissures that open up in a symmetric fashion (two sets, one on each side of the volcano).

My guess is that this happens when either the conduit gets plugged or too much magma rises at once for the conduit to handle. That latter possibility is the most likely one for a major eruption during this unrest, because Aira caldera is inflating and they say it's already at the level it was before the 1914 eruption (Japan coincidentally had done leveling surveys before that and they repeated them afterwards, finding that southern Kyushu's ground level had dropped, particularly around Kagoshima Bay).

Thus far, Sakurajima has been able to blow off the inflationary pressure. And at the moment, JMA does not report inflation, so good news. For now.</layperson opinion>

 

[bjdeming]

JMA update today (per Google Translate) mentions the frequent blasts but overall is the same.

I added a link.

Status of volcanic activity​

　Active eruption activity continues at Sakurajima.
　
　Ten eruptions occurred at the Minamidake summit crater. The volcanic smoke reached a maximum height of 1,800 meters above the crater rim. Also, at the same crater, fire reflections were observed at night using a highly sensitive surveillance camera.
　
　No eruption or fire eruption has been observed at the Showa crater.
　
　The number of volcanic earthquakes has remained low. Volcanic tremors occurred due to the eruption.
　
　According to a field survey conducted yesterday (2nd), the amount of volcanic gas (sulfur dioxide) released was slightly higher at 1,300 tons per day (previously on October 25, it was 2,200 tons).
　
　Continuous GNSS observations have shown that some baselines within Sakurajima Island have been slightly elongated since around January 2023, likely due to the expansion of the mountain, but this has been stagnant since around April. Additionally, along the baseline that spans the Aira Caldera (inner part of Kagoshima Bay), gradual elongation has been observed over a long period of time, indicating expansion of the deep underground of the Aira Caldera.
　
　At Sakurajima, magma has accumulated for a long time deep underground in the Aira Caldera (inner part of Kagoshima Bay), and the amount of volcanic gas (sulfur dioxide) released is generally large, so the Minamidake summit crater and the Showa crater Eruptive activity is expected to continue in the future. Please pay attention to future volcano information.
　

It seems counterintuitive to say, oh, yeah, it's erupting but there's no immediate risk of it erupting, but there we are -- open conduit (good!).

The SO2 is fairly low; the volcanic edifice is not inflating at the moment; and magma keeps flowing into the deeper reservoir (Aira Caldera).

 

[bjdeming]

Sakurajima took a feeble but impressive-looking swipe at the sky on December 12th, with interesting plume dynamics --



-- but it is still at that mildly elevated level, higher than the soccer-game-background days but nowhere near the intensity of that recent lightning-charged blast.

JMA says it is not inflating again. Yet. Aira Caldera's inflation continues as it has been doing for a while now.

 

[bjdeming]

Sakurajima had a strong but mostly harmless blast today, with the plume reaching 5 km for the first time since 2020.



JMA released a statement (autotranslated), but they don't mention deformation and they kept the alert at Level 3, so it remains to be seen whether this is a one-off event or the start of an activity intensification.