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[HDS07-P09] Movement characteristics of Gampei landslide in Joetsu City during winter
Keywords:landslide, Neogene layer, snowfall, pore water pressure
Landslides in the Neogene strata of the heavy snowfall regions in Niigata Prefecture have been reported to be active not only during rainfall and snowmelt periods but also during the snowy season (Sato et al., 2004). It is believed that snow load and groundwater level fluctuations due to snowmelt contribute to landslide activity during the snowy season. However, due to the limited number of observation cases, the specific mechanisms remain insufficiently understood. To gain a deeper understanding of landslide characteristics in heavy snowfall regions and apply this knowledge to disaster prevention measures, further accumulation of observational data is necessary.
Inoue et al. (2025) found that the Ganpei landslide has been continuously active since around 2010, with larger displacement during winter than in summer, greater movement in years with less snowfall compared to heavy snowfall years, and no significant increase in displacement during snowmelt or rainfall events. The Ganpei landslide is located in the Higashikubiki Hills of Joetsu City, Niigata Prefecture, within the Neogene strata, and has been managed as a designated landslide area since 1961. This study focused on the III-D block, where no preventive construction has been carried out. The III-D block has a total length of approximately 800 m, a width of about 150 m, a sliding surface depth of around 7 m, and a slope of about 13°. It is situated in a heavy snowfall area, with a snow depth reaching approximately 3 m during the winter of 2020/2021. Movement continues throughout the year, with a tendency for greater displacement during the snowy season, particularly in years with less snowfall.
This study aimed to clarify the factors influencing landslide activity during the snowy season by observing displacement, groundwater level, pore water pressure, soil moisture, ground temperature, and snow accumulation in the Ganpei landslide in Joetsu City, Niigata Prefecture. To investigate the relationship between displacement and groundwater level, a manual drilling machine was used to excavate to a depth of 11 m, and extensometers, pore water pressure gauges, water level meters, soil moisture sensors, and ground temperature sensors were installed. Additionally, a time-lapse camera was set up to observe snow depth, and GNSS surveying was conducted for continuous displacement monitoring. The observation equipment was installed at the central part of the moving mass, where displacement was the greatest. The extensometer observations began in May 2024, while the other instruments started in December 2023. Furthermore, to capture surface changes in the moving mass, UAV-based LiDAR observations were conducted, acquiring point cloud data before snowfall (November) and after snowmelt (May). The acquired data were analyzed using Mierre by Central Japan Aviation Inc.
Observations confirmed that the movement of the Ganpei landslide was significantly subdued in the long term due to the impact of the Noto Peninsula earthquake that occurred on January 1, 2024. Additionally, data from the pore water pressure gauges and water level meters revealed that the groundwater level fluctuates seasonally. In particular, during winter, the groundwater level remained relatively stable and was less affected by rainfall or snowmelt. In contrast, during summer, the groundwater level exhibited greater fluctuations, and in autumn, when rainfall increased, the groundwater level was observed to rise.
Inoue et al. (2025) found that the Ganpei landslide has been continuously active since around 2010, with larger displacement during winter than in summer, greater movement in years with less snowfall compared to heavy snowfall years, and no significant increase in displacement during snowmelt or rainfall events. The Ganpei landslide is located in the Higashikubiki Hills of Joetsu City, Niigata Prefecture, within the Neogene strata, and has been managed as a designated landslide area since 1961. This study focused on the III-D block, where no preventive construction has been carried out. The III-D block has a total length of approximately 800 m, a width of about 150 m, a sliding surface depth of around 7 m, and a slope of about 13°. It is situated in a heavy snowfall area, with a snow depth reaching approximately 3 m during the winter of 2020/2021. Movement continues throughout the year, with a tendency for greater displacement during the snowy season, particularly in years with less snowfall.
This study aimed to clarify the factors influencing landslide activity during the snowy season by observing displacement, groundwater level, pore water pressure, soil moisture, ground temperature, and snow accumulation in the Ganpei landslide in Joetsu City, Niigata Prefecture. To investigate the relationship between displacement and groundwater level, a manual drilling machine was used to excavate to a depth of 11 m, and extensometers, pore water pressure gauges, water level meters, soil moisture sensors, and ground temperature sensors were installed. Additionally, a time-lapse camera was set up to observe snow depth, and GNSS surveying was conducted for continuous displacement monitoring. The observation equipment was installed at the central part of the moving mass, where displacement was the greatest. The extensometer observations began in May 2024, while the other instruments started in December 2023. Furthermore, to capture surface changes in the moving mass, UAV-based LiDAR observations were conducted, acquiring point cloud data before snowfall (November) and after snowmelt (May). The acquired data were analyzed using Mierre by Central Japan Aviation Inc.
Observations confirmed that the movement of the Ganpei landslide was significantly subdued in the long term due to the impact of the Noto Peninsula earthquake that occurred on January 1, 2024. Additionally, data from the pore water pressure gauges and water level meters revealed that the groundwater level fluctuates seasonally. In particular, during winter, the groundwater level remained relatively stable and was less affected by rainfall or snowmelt. In contrast, during summer, the groundwater level exhibited greater fluctuations, and in autumn, when rainfall increased, the groundwater level was observed to rise.