Preprints
https://doi.org/10.5194/esurf-2021-41
https://doi.org/10.5194/esurf-2021-41

  26 May 2021

26 May 2021

Review status: this preprint is currently under review for the journal ESurf.

Temporal changes in the debris flow threshold under the effects of ground freezing and sediment storage on Mt. Fuji

Fumitoshi Imaizumi1, Atsushi Ikeda2, Kazuki Yamamoto3, and Okihiro Osaka4 Fumitoshi Imaizumi et al.
  • 1Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8429, Japan
  • 2Faculty of Life and Environmental Sciences, University of Tsukuba, 305-8572, Japan
  • 3Bureau of Economic Affairs, Shizuoka city office, Shizuoka, 422-8429, Japan
  • 4Shizuoka Professional University of Agriculture, Japan, 424-8701

Abstract. Debris flows are one of the most destructive sediment transport processes in mountainous areas because of their large volume, high velocity, and kinematic energy. Debris flow activity varies over time and is affected by changes in hydrogeomorphic processes in the initiation zone. To clarify temporal changes of debris flow activities in cold regions, the rainfall threshold for the debris flow occurrence was evaluated in Osawa failure at a high elevation on Mt. Fuji, Japan. We conducted field monitoring of the ground temperature near a debris flow initiation zone to estimate the presence or absence of seasonally frozen ground during historical rainfall events. The effects of ground freezing and the accumulation of channel deposits on the rainfall threshold for debris flow occurrence were analyzed using rainfall records and annual changes in the volume of channel deposits since 1969. Statistical analyses showed that the intensity-duration threshold during frozen periods was clearly lower than that during unfrozen periods. A comparison of maximum hourly rainfall intensity and total rainfall also showed that debris flows during frozen periods were triggered by a smaller magnitude of rainfall than during unfrozen periods. Decreases in the infiltration rate due to the formation of frozen ground likely facilitated the generation of overland flow, triggering debris flows. During unfrozen periods, the rainfall threshold was higher when the volume of channel deposits was larger. Increases in the water content in channel deposits caused by the infiltration of rainfall is likely important for the debris flow occurrence during unfrozen periods. The results suggest that the occurrence of frozen ground and the sediment storage volume need to be monitored and estimated for better debris flow disaster mitigation in cold regions.

Fumitoshi Imaizumi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2021-41', Anonymous Referee #1, 22 Jun 2021
    • AC1: 'Reply on RC1', Fumitoshi Imaizumi, 01 Jul 2021
  • RC2: 'Comment on esurf-2021-41', Francis Rengers, 30 Jul 2021

Fumitoshi Imaizumi et al.

Fumitoshi Imaizumi et al.

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Short summary
The rainfall threshold for the debris flow occurrence was evaluated on Mt. Fuji, Japan. Debris flows during frozen periods were triggered by a smaller magnitude of rainfall than during unfrozen periods. During unfrozen periods, the rainfall threshold was higher when the volume of channel deposits was larger. The results suggest that the occurrence of frozen ground need to be monitored for better debris flow disaster mitigation in cold regions.