NAN, Thailand – A mountain slope in Tha Wang Pha district has collapsed further during the rainy season, with the affected area expanding from about 2 metres last year to more than 100 metres and raising concerns over the safety of Ban Doi Tiew School and nearby homes.
Officials from the Nan Provincial Office of Natural Resources and Environment, together with geologists and representatives from local agencies, inspected the site in Ban Doi Tiew, Si Phum subdistrict, after reports of continued ground movement.
The inspection found extensive subsidence and several landslide scars around the school, located at an elevation of about 1,116 metres above sea level. Cracks and fractures were also found in the school buildings, multipurpose building and other structures, indicating movement of the ground beneath the site.
Local residents reported that the area first experienced a landslide between May and July 2025. At that time, the affected section was about 2 metres wide. During this year’s rainy season, the collapse expanded to more than 100 metres, with additional cracks and fissures appearing across the area.
Geologists found that the site is underlain by reddish-brown siltstone and shale. The rock has a relatively high degree of weathering, contributing to a thick layer of clay-rich soil covering the slope.
The geological conditions increase the possibility of further ground movement and landslides, particularly during periods of heavy rainfall. The Department of Mineral Resources had previously classified the area as having a moderate to very high risk of landslides.
Following the inspection, the Office of Mineral Resources Region 1 prepared a report detailing its findings and recommendations and submitted it to the Nan Provincial Office of Natural Resources and Environment for consideration and further action. Officials are continuing to assess the unstable area, with particular attention to the expanding ground collapse and damage to structures at Ban Doi Tiew School.
