# Assessment of Internal and External Factors Causing Slow-Moving Landslides
## 4 Conclusions  
The phenomenon of slow-moving landslides is one of the most frequent landslide hazards caused by a combination of various factors. Slow-moving landslides can occasionally accelerate rapidly and collapse catastrophically [17]. As opposed to landslides, slow-moving landslides have not been actively studied until recently, and we need to conduct various studies on their triggering factors. This should lead to the development of early warning systems at the national level to minimize the damage to infrastructure and local communities caused by slow-moving landslides. In this study, the landslide hazard map and the slow-moving landslide area were overlapped for analysis to investigate the difference in the occurrence of landslides and slow-moving landslides using GIS. Consequently, it was inferred that slow-moving landslides occur mainly in areas with low risk ratings on the landslide hazard map, particularly in excluded areas (non-hazardous areas). Until recently, the phenomenon of slow-moving landslides has been treated as a type of landslide in South Korea. However, unlike landslides, which are a type of surface failure type of mountain erosion, slow-moving landslides can cause large-scale damage to human life, property, and social infrastructure because the soil layer moves slowly for a long time. Predicting and responding to the risk of slow-moving landslides is impossible with a landslide hazard map. Hence, slow-moving landslides should be regarded as a distinctly different phenomenon from landslides. The establishment of a national SMLHIS (slow-moving landslide hazard map) is urgently needed. Slow-moving landslides were found to occur most frequently in the Gyeongsang supergroup, which corresponds to sedimentary rocks. Slow-moving landslides also occurred in igneous, metamorphic, and sedimentary rocks, but slow-moving landslides were more likely to occur when the grain of the rock was the same as the slope degree direction. Soil textures were found most frequently in sandy loam. The results of this study are expected to help to understand the causes of slow-moving landslides related to soil factors and to prepare measures to prevent slow-moving landslides. However, slow-moving landslides were relatively more likely to occur due to intensive rainfall, particularly when the continuous rainfall was more than 100 mm and the 15-day antecedent rainfall was more than 200 mm. Furthermore, slow-moving landslides are caused by the influence of intensive rainfall in addition to internal factors such as strata or topography that are vulnerable to slow-moving landslides. The width and length of the slow-moving landslide area were significantly and positively correlated with continuous rainfall days before the slow-moving landslide occurred. The depth of the slow-moving landslide area was significantly and positively correlated with rainfall on the date of slow-moving landslide; maximum hourly rainfall; and three-, five-, and 7 seven-day antecedent rainfall. The width and length of the slow-moving landslide area were significantly and positively correlated with rainfall intensity during the slow-moving landslide. These results suggest that slow-moving landslides are triggered by both the amount and intensity of rainfall. In particular, the longer the number of continuous rainfall days before the slow-moving landslide occurred; the greater the rainfall on the date of slow-moving landslide;the maximum hourly rainfall; the three, five, and seven-day antecedent rainfall; and the greater the rainfall intensity at the time of slow-moving landslide occurrence, the greater the magnitude of slow-moving landslide. Slow-moving landslides, which are not easy to detect, can cause forest disasters such as large-scale forest collapse and sediment runoff. Therefore, to prevent slow-moving landslides, it will be necessary to protect forests in preparation for intensive rainfall and to identify slow-moving landslide-vulnerable areas through the establishment of an SMLHIS to undertake appropriate preventive measures.