In the mountainous areas of northern Vietnam, many landslides occur every year during the rainy season and typhoons. Landslide damage has affected many villages and mountain slopes, such as road slopes and terraced rice paddies, in relation to recent climate change and rapid development in Vietnam. Therefore, there is an urgent need to establish an early warning evacuation system for landslides. However, the construction of a highly accurate landslide warning system remains difficult because of insufficient data on the factors affecting landslide occurrence, such as rainfall, geology, and groundwater. The objective of this study is to clarify the relationship between landslide occurrence and geology, geological structures, and rainfall in northern Vietnam, based on detailed data reported from the State-Funded Landslide Project, a Vietnam-funded landslide project started in 2012. Research has revealed that the scales, types of movement, and distribution of these landslides are strongly affected by the geology, geological structure, and weathering of rocks. An outline of the relationship between precipitation and landslides was also obtained. These results are useful indicators for determining future landslide hazard areas and thresholds for warning and evacuation systems.

  On March 14, 2022, a landslide occurred in Yanaizu Town, Fukushima Prefecture, Japan. This landslide is notable in that it occurred during the snowmelt season in the distribution area of Tertiary tuff, so-called “Green tuff”. Field survey and measurements were carried out for this landslide. In this paper, it is described those results and the examination of the process based on them. The results are as follows ;

  The excavation works were carried out on this slope until July 2021 and the slope was stabilized. This slope was composed of tuffaceous coarse-grained sandstone, “Green tuff”. A tuffaceous siltstone beds were distributed in this sandstone layer with a dip structure. This layer deteriorated due to slaking with stress relaxation associated with construction work. In addition, topography and groundwater infiltration conditions had changed. The rise up the groundwater level during the snowmelt season acted on this situation, triggering the slide. These processes are confirmed by slope stability calculations.

”Green tuff”, which is widely distributed mainly in eastern Japan, is known to contain smectite clay minerals such as chlorite. The “Green tuff” layer looks rocky, and its slopes seem mechanically stable. However, it is necessary to pay attention to its deterioration, when the tuffaceous siltstone beds are distributed into the slope.