BJ Deming

Merapi updates (Dec. 11, 2025, 0046 UTC)

December 10, 2025, 4:46 p.m., Pacific: It has been a long time since my last update, and Merapi has carried on at its usual level — see the Global Volcanism Program (GVP) page for interim details.

Per the last GVP report:

Most Recent Weekly Report: 26 November-2 December 2025

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Merapi continued during 26 November-2 December. The seismic network recorded the descent of pyroclastic flows during 27-28 and 30 November. The SW lava dome produced nine lava avalanches that traveled as far as 1.9 km SW down the Bebeng drainage on 28 November, one that traveled 1.8 km down the Bebeng drainage on 30 November, 19 that traveled as far as 1.7 km SW down the Krasak drainage on 1 December, and six that traveled 2 km W down the Sat/Putih drainage. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit, based on location.

March 3, 2023, 9:48 a.m., Pacific: First, a stocks and bonds point of view.

Next, wow! Check out that coulee!

https://platform.twitter.com/widgets.js

And this, translated via Twitter as:

Survey Results of the Geological Agency Drone Team After the Awanpanas Drop Incident on 11-12 March 2023

On March 11-12 2023, Mount Merapi launched a hot cloud towards Kali Bebeng. Until now, Monday, March 13 2023, there have been 60 incidents of hot clouds falling on Mount Merapi.

https://platform.twitter.com/widgets.js

The volcano’s status is unchanged at the time of writing.

The boffins will have the last word, of course, but this looks to me (a layperson) like one of Merapi’s typical, if rather emphatic, dome-demolition/pyroclastic flow making events; and now, apparently, it’s going to build a new dome in the same spot on the southwest flank.

Meanwhile, there is also an active dome in the summit crater to keep an eye on.

Finally, for now, here is what fallout from the flow clouds did to the nearby city of Magelang. The rainy season is still on, and lahars will be a problem everywhere in the affected area.

https://platform.twitter.com/widgets.js

Initial update:

This is in conjunction with yesterday’s post — so long and involved that it seemed better to put updates here.

And there are updates!

For example, as of around 2:30 p.m., Pacific (2130 UTC) on March 12, 2023, it appears from this image tweeted about three hours ago that there’s a lava coullee on the flank:

https://platform.twitter.com/widgets.js

That is yet to be confirmed, as far as I know.

But this sure looks like sticky lava erupting, presumably at or near the (former?) location of the lava dome high up on the southwestern flank:

https://platform.twitter.com/widgets.js

As for the lightning, WELL!

https://platform.twitter.com/widgets.js

That is meteorological, not volcano generated, AFAIK.

The monsoon rains are still on, I think, but that formation is amazing, rainy season or not.

And this was tweeted about 13 hours ago:

https://platform.twitter.com/widgets.js

If the boffins aren’t sure, I’m not speculating, either. I just note that:

  • Per my reading (Chaussard et al.), Merapi is an open-conduit system and only deforms up near the summit, which is presumably where this western flank deformation is;
  • A lava intrusion could explain the deformation.

More updates (front-loaded) as they become available.

Sources quoted:

Chaussard, E.; Amelung, F.; and Aoki, Y.
2013. Characterization of open and closed volcanic systems in Indonesia and Mexico using InSAR time series. Journal of Geophysical Research: Solid Earth, 118(8): 3957-3969.

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