Following the passage Typhoon Podul, the lake created by this massive landslide has now grown considerably. Overtopping is expected in October, although could occur sooner if further heavy rainfall occurs.
The landslide-dammed lake behind the the enormous 21 July 2025 rock avalanche in the Matia’an valley, in Wanrong township in eastern Taiwan continues to fill. Meanwhile, the landslide itself is evolving with time. This is a Planet Labs image of the site soon after the main rock avalanche occurred:-
Planet Labs image showing the site of the 21 July 2025 landslide in the Matia’an valley in Wanrong township, Taiwan. Satellite image copyright
Planet Labs , used with permission. Image dated 25 July 2025.
Whilst this is the most recent satellite image (note that the right hand side is the older image):-
Recent
Planet Labs image showing the site of the 21 July 2025 landslide in the Matia’an valley in Wanrong township, Taiwan. Satellite image copyright
Planet Labs, used with permission. Image dated 18 August 2025.
And here is a slider so that you can compare the two images:-
Image copyright Planet Labs.
This area received very heavy rainfall as a result of the passage of Typhoon Podul. This has driven a number of changes. Perhaps most obviously, the lake is now very considerably larger. This will continue to grow over the coming weeks until overtopping occurs.
Second, as I noted in my original post, the landslide generated a large volume of dust which had settled around the deposit, especially to the south. This has now been washed away.
Thirdly, there have been more failures from the rear scarp of the landslide, so the landslide deposit has evolved.
And finally, the heavy rainfall has driven some erosion of the finer-grained portions of the landslide deposit.
It is also worth noting that a few other, smaller, lakes have now formed on the landslide. The largest of these is about 250 x 200 metres, so not insignificant.
On 14 August 2025, etaiwan.news posted an article in Mandarin about the landslide. It noted that the Taiwan Government has authorised funding to “develop disaster mitigation, monitoring, evacuation, and engineering plans”. This includes the development of an evacuation plan, but also “evaluation and planning, excavation of spillways, construction of embankments, bed consolidation, etc., to reduce the risk of dam collapse and protect downstream areas”.
The Hualien Branch of the Forestry and Conservation Department has released these two images of the lake at the site of the in the Matia’an valley:-
The deposit of the 21 July 2025 landslide in the Matai’an valley in Wanrong township, Taiwan. Image by provided by Hualien Branch of the Forestry and Conservation Department/Wang Zhiwei Hualien Fax.
The deposit of the landslide is well-captured, with the lake in the background. This is the same site from the lake looking towards the toe:-
The lake formed by the 21 July 2025 landslide in the Matai’an valley in Wanrong township, Taiwan. Image by provided by Hualien Branch of the Forestry and Conservation Department/Wang Zhiwei Hualien Fax.
Immediately after the typhoon, the lake had reached 43% of its storage capacity with a freeboard of 55 metres. Assuming that no further typhoons affect this area, and in the absence of the construction of a spillway, overtopping is likely to occur in October.
Reference
Planet Team 2025. Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/
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