Red alert issued as Super Typhoon Ragasa threatens dammed lake overtopping, Taiwan
Around 1 800 homes were evacuated from villages in Taiwan’s Hualien County on September 22, 2025, due to the risk of Matai’an Creek dammed lake overflowing.
A recent photograph of the Matai’an landslide dam in Taiwan. Credit: Forestry and Conservation Department
A red alert was issued for the region at 07:00 local time on September 22, mandating evacuations of around 1 800 homes in the following villages:
Daping Village, Daquan Village, Datong Village, Daan Village, Dama Village, Dahua Village, Dajin Village, Beifu Village, Xifu Village, Dongfu Village and Mingli Village in Wanrong Township, as well as Changqiao Village in Fenglin Township.
This comes as Super Typhoon Ragasa threatens the mountainous region with 500 to 800 mm (20 to 31 inches) of rain, causing fear of flash flooding and landslides for these downstream communities, due to lake overtopping.
The lake in question had formed due to a large rock avalanche in the region earlier this year on July 21. The mass movement blocked the valley floor and impounded a growing barrier lake.
This was the Matai’an Creek dammed lake, with an estimated overtopping volume of 86 million m3 (3 billion feet3).
The landslide deposit consists of coarse rock debris that forms a natural dam. While such dams can be relatively porous, fine-grained material may reduce seepage, increasing the likelihood of overtopping.
While back estimates said that overtopping should occur sometime in mid-October, due to influence of Ragasa the lake could overflow by September 24; thus, prompting the evacuations.
The evacuations are currently ongoing as height differences between the villages have slowed the process.
References:
1 雨量恐致馬太鞍溪堰塞湖溢流 啟動撤離估1800戶 – CNA – September 22, 2025
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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