Every year, especially in the rainy season, landslides occur quite often in Lao Cai – a northern mountainous province of Vietnam. Specifically, in the year 2019, several landslides were observed to occur near the Sapa Ancient Rock Field in Hau Thao commune, Sapa town, Lao Cai province. In December 2019, a landslide investigation was conducted to examine the mechanism and possible causes of the landslides. Besides that, as the landslide distribution in this area is still unclear, this study will also aim to show the landslide denseness in a 700 m × 700 m square map as well as survey results in 2019 of two main landslides in such map. According to the survey, the landslide is the main phenomenon of geomorphological development in this area, being a combination of multiple different landslides with varying sizes and dissimilar triggers. The first survey landslide is about 50 m wide and 350 m long and has still been going on in recent years, with annual horizontal displacement being around 0.8 m. Meanwhile, the second one is a typical flash-landslide caused by rainfall. Despite being quite small in scale, about 15 m × 40 m, its characteristics indicate a dangerous implication in the future. This information will be the basis for further ongoing studies.

1. [1] D. T. Bui, T. A. Tuan, N.-D. Hoang, N. Q. Thanh, D. B. Nguyen, N. V. Liem, and B. Pradhan, “Spatial prediction of rainfall-induced landslides for Lao Cai area (Vietnam) using a hybrid intelligent approach of least support vector machines inference model and artificial bee colony optimization,” Landslides, Vol.14, No.2, pp. 447-458, 2017.
2. [2] T. V. Tran, V. H. Hoang, H. D. Pham, and G. Sato, “Use of Scoops3D and GIS for the Assessment of Slope Stability in Three-Dimensional: A Case Study in Sapa, Vietnam,” Proc. of the Int. Conf. on Innovations for Sustainable and Responsible Mining, Lecture Notes in Civil Engineering, Vol.108, pp. 210-229, 2020.
3. [3] T. V. Tran, M. T. Trinh, G. Lee, S. Oh, and T. H. V. Nguyen, “Effect of Extreme Rainfall on Cut Slope Stability: Case Study in Yen Bai City, Viet Nam,” J. of the Korean Geo-Environmental Society, Vol.16, No.4, pp. 23-32, 2015.
4. [4] T. V. Tran, D. Alkemab, and R. Hack, “Weathering and deterioration of geotechnical properties in time of groundmasses in a tropical climate,” Engineering Geology, Vol.260, Article 105221, 2019.
5. [5] N. B. Duan, D. T. Hai, D. V. Minh, and L. T. T. Hien, “Studying to determine causes of landslide in the area of the Mong Sen bridge, Lao Cai province,” Vietnam J. of Earth Sciences, Vol.33, pp. 164-174, 2011 (in Vietnamese).
6. [6] C. V. Ngoi and N. T. T. Ha, “Assessment of landslide hazards along the national road 4D focusing on the relationship between geologic structures and topology,” Vietnam J. of Earth Sciences, Vol.305, pp. 1-8, 2008 (in Vietnamese).
7. [7] D. M. Nguyen and Q. H. Tran, “Features of large-scale landslide at Hau Thao area, Sa Pa town, Lao Cai province,” Geotechnics for Sustainable Infrastructure Development, pp. 917-922, 2019.
8. [8] P. H. Giao and B. X. Hanh, “Analysis of post-landslide electric imaging data at a site in Sapa, Vietnam,” Conf. Proc., EAGE-GSM 2nd Asia Pacific Meeting on Near Surface Geoscience and Engineering, Kuala Lumpur, pp. 1-5, 2019.
9. [9] B. P. My and N. V. Hoanh (Eds.), “Geological and Mineral Resources Map of Viet Nam on 1:200.000, Kim Binh – Lao Cai zone (F-48-VIII&F-48-XIV),” Department of Geology and Minerals of Viet Nam, Ha Noi, 2005.
10. [10] M. Kottek et al., “World Maps of Köppen-Geiger Climate Classification; Version March 2017,” http://koeppen-geiger.vu-wien.ac.at/present.htm [accessed October 12, 2020]
11. [11] Climate-Data.Org, “Sa Pa Climate (Vietnam),” https://en.climate-data.org/asia/vietnam/lao-cai-province/sa-pa-36229/ [accessed October 12, 2020]
12. [12] “Rain gauges in Laocao, Vietnam,” https://vrain.vn/ (in Vietnamese) [accessed November 1, 2020]
13. [13] “Landslide in Sapa: One person was buried dead,” https://tuoitre.vn/sat-lo-dat-o-sa-pa-mot-nguoi-bi-vui-lap-chet-2019080515083918.htm/ [accessed September 15, 2020]
14. [14] T. Danjo and T. Ishizawa, “Quantitative Evaluation of the Relationship Between Slope Gradient and Infiltration Capacity Based on a Rainfall Experiment Using Pit Sand,” J. Disaster Res., Vol.15, No.6, pp. 745-753, 2020.