Abstract Landslides are known as widespread natural hazards. The formation of landslide dams, or landslide deposits, functions as a part of cascading geohazards. Recent studies have revealed the effects of landslide deposits on aquatic geochemistry and ecosystems. However, the role of landslide deposits in shaping subsurface redox conditions, closely linked to biogeochemical element cycles, remains unexplored. Herein, we applied electrical resistivity tomography (ERT) and self-potential (SP) surveys to investigate the subsurface structure, groundwater flow patterns, and redox conditions of a landslide deposit formed by shallow landslides that occurred during the 2018 Hokkaido Eastern Iburi earthquake in Japan (M w 6.6). The ERT results revealed the soil–bedrock interface as a zone of 20–40 Ω·m with an abrupt spatial change. The soil zone had a maximum thickness of ~ 8 m and a groundwater table at ~ 2 m below ground. The measured SP values ranged from − 28.4 to 15.4 mV. The SP trend surface, which represents the linear trend in the spatial distribution of SP values, showed that SP values increase with decreasing elevation and in the downstream direction, suggesting a gaining-stream condition. Positive SP anomalies were primarily attributed to streaming potential driven by the hydraulic gradients, whereas negative SP anomalies were associated with redox gradients induced by a biogeobattery system with reducing soil zones. These results suggest that landslide deposits host spatially heterogeneous redox environments. Such environments facilitate the mobilization of redox-sensitive metals such as Mn and Fe, thereby posing risks to downstream hydrochemistry and aquatic ecosystems. To our knowledge, this is the first application of geophysical methods to estimate the spatial patterns of redox conditions within a landslide deposit, providing insights into freshwater resource management and ecosystem functioning in landslide-prone catchments. Integrating geophysical, hydrochemical, and microbiological approaches will enable us to reveal the underexplored environmental impacts of landslide deposits.
Yoshihara et al. (2026) studied this question.