Multi-Temporal Analysis of Scarp Expansion in the Kamitokitozawa Landslide: Insights from Tree-Ring, UAV Data, and Google Earth Imagery

The expansion of tension cracks, step-like terrain, and other features associated with landslide reactivation is prominent phenomena within the landslide area, making the investigation of their temporal development essential for understanding landslide dynamics. In this study, we aim to examine the temporal development of an NW-SE trending counter scarp with a height up to approximately 3 m within the Kamitokitozawa landslide in Akita prefecture, Japan, using a combination of multiple approaches. The approaches include dendrogeomorphological analyses, such as analyzing tree-ring eccentricity, the recovery age of stem wounding caused by landslides in 11 disks from Cryptomeria japonica, and the establishment ages of shade-intolerant tree species, along with interpretations of multi-temporal Google Earth imagery and topographic data derived from a laser-equipped UAV. These approaches allow us to reconstruct the multiple stages of scarp development, which may have initially formed on its southeast side, creating a forest gap in 2010, based on Google Earth imagery and subsequent expansions of the scarp. Dendrogeomorphological analyses indicate expansions during 2016–2017 and 2020–2021, based on the recovery age of stem wounding, as well as during 2019–2023, based on the establishment ages of shade-intolerant tree species. Additionally, 13 events spanning from 1995 to 2021 were identified from tree-ring eccentricity, with a notable clustering around 2018–2021. Additionally, expansions of the scarp were captured in 2019, 2021, 2022, and 2023 based on the UAV topographic data.