Topography and geology effects on travel distances of natural terrain landslides: Evidence from a large multi-temporal landslide inventory in Hong Kong

Landslides pose threats to the safety and property of people living in mountainous areas like Hong Kong. Dependence of landslide travel distance on initial conditions and travel routes has broad implications for assessing the landslide risks. In this study, the controlling topographic and geologic factors for travel distances of open hillslope landslides and channelized debris flows are examined based on the Enhanced Natural Terrain Landslide Inventory (ENTLI) in Hong Kong with 11,622 records during the period of 1984–2013. The mean values of the horizontal travel distances of open hillslope landslides and channelized debris flows are 24.1 and 86.3 m, respectively. Correlations combining horizontal travel distances, volumes and fall heights of open hillslope landslides have been derived. The horizontal travel distances (L) and fall heights (H) are closely related for both types of landslides. The use of the L/H ratio alone as a representation of natural terrain landslide mobility is not suggested. Because of the entrainment of loose materials, the travel distances of channelized debris flows are enlarged significantly on colluvium lands (with mean value of 142.6 m), compared with those on weathered mantles (with mean value of 74.2 m).