Landslide longitudinal shape: a new concept for complementing landslide aspect ratio

Aspect ratio is an elementary parameter widely adopted to characterize landslide geometry. Nevertheless, it in essence reflects an overall elongation of landslide only, and cannot reflect the variation of width along the central line of movement. This paper proposes the new concept landslide longitudinal shape for complementing the landslide aspect ratio, and develops the methodology for interpreting it based on generation and analysis of the landslide profile. Relative width change and relative width fluctuation are defined as parameters quantitatively describing landslide longitudinal shape, and five different types of shape (rectangle, widening, narrowing, spindle, and hourglass) are predefined for qualitatively classifying it. A case study showed that landslide longitudinal shape can provide additional information and therefore is a complement to the aspect ratio. Landslides with larger aspect ratios (more elongated) are more possibly characterized by a narrowing overall varying trend and a stronger fluctuation of width. Landslides with similar longitudinal shapes of headscarp zones were found to have transition-deposition zones with diverse longitudinal shapes, which is caused by diverse topographic confinements and forces governing motion. For an unconfined and laterally confined landslide in the study area, its transition-deposition zone is most likely to have a regular and narrowing longitudinal shape, respectively. Longitudinal shape is not just a geometric parameter, but can somehow help to understand motion constraints of landslides. It must be emphasized that the new longitudinal shape concept is not applicable to landslides that show a complex geometry that prevents a clear definition of a longitudinal profile.

Automated summary

Aspect ratio is insufficient in characterizing the geometry of landslides. This paper introduces the concept of landslide longitudinal shape as a complement to the aspect ratio. The longitudinal shape is determined by the relative width change and fluctuation, and can provide additional information about landslides.