Failure of the landslide debris from the Matai’an rock avalanche allowed another barrier lake to form. This breached on 21 October 2025, generating another damaging debris flow.
Newspapers in Taiwan are reporting that a new landslide barrier lake formed and then failed at the site of the giant Matai’an rock avalanche. The breach event apparently occurred at baout 9 pm local time on 21 October 2025. The risk had been identified in advance and the downstream population had been evacuated successfully this time, so there are no reports of fatalities.
The Taipei Times has an image of the barrier lake that was released by the Hualien branch of the Forestry and Nature Conservation Agency:-
There is also a video on Youtube from Focus Taiwan (CNA English News) that includes helicopter footage of the site, also provided by the Forestry and Nature Conservation Agency:-
This includes the following still:-
It appears to me that the barrier lake has formed because of a large landslide in the debris from the original rock avalanche note the dark coloured landslide scar on the left side of the image.
Loyal readers will remember that I highlighted that this could be an issue in my post on 3 October:-
“So, a very interesting question will now pertain to the stability of these slopes. How will they perform in conditions of intense rainfall and/or earthquake shaking? Is there the potential for a substantial slope failure on either side, allowing a new (enlarged) lake to form.”
“This will need active monitoring (InSAR may well be ideal). The potential problems associated with the Matai’an landslide are most certainly not over yet.”
There is a high probability that this will be a recurring issue in periods of heavy rainfall.
Meanwhile, keep a close eye on Tropical Storm Melissa, which is tracking slowly northwards in the Caribbean. This could bring exceptionally high levels of rainfall to Haiti and Jamaica as it is moving very slowly. This one looks like a disaster in waiting at the moment.
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