The evolution of the Wanlixi landslide in Taiwan

The Wanlixi landslide in Taiwan has undergone significant evolution since its initial observation on June 21, 2026, as highlighted by Planet Labs satellite imagery. Initially, on June 20, 2026, the slope was intact, but signs of distress were evident on the eastern side, accompanied by substantial dust accumulation. By April 14, 2026, approximately nine weeks prior to the failure, the landslide exhibited minimal dust, indicating slower deformation.

This period showcased the western side's dramatic fragmentation and downslope movement, contrasting with the relatively stable eastern side.

Following the main failure on June 21, 2026, the landslide showed ongoing dynamics. Recent imagery from July 9, 2026, revealed a clearly visible lake in the northwest corner, with dust on the eastern side indicative of rockfall activity following heavy rainfall. Comparing the July 9 image with the day of failure highlights the landslide's retreat and westward creep, particularly noticeable on the western side. This movement is evident in the intact vegetation rafts, emphasizing the landslide's ongoing shift.

Two key insights emerge from this imagery. First, the Planet Labs imagery could serve as an early warning tool, tracking landslide development and identifying signs of instability such as dust accumulation. Machine learning could potentially enhance this capability across broader areas. Second, the landslide's continued movement, especially on the western side, exerts pressure on the natural spillway, potentially explaining the dam's current structural integrity.

As Taiwan enters typhoon season, the risk of heavy rainfall could further influence the landslide's behavior, making continued monitoring crucial.