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[MZZ52-04] The geological influence for landslides by artificial terrain change of medieval mountain castle ruins
Keywords:Survey sketch of ruin, Ratio of collapse area, Soil analysis
More than 40% of the medieval castle ruins had many landslides in them lower slope when the torrential rain in July 2018 in Higashihiroshima City.
The author indicated with the results of field work that the dry moat of medieval mountain castle ruins caused some landslides (Inomata, 2021, under review).
The purpose of this study was to investigate whether the risk of medieval mountain castle ruins is a region-specific risk. Therefore, that focused on the geology and analyzed the following three items.
1. Confirmation of past landslides on survey sketch of ruins
2. The ratio of collapse area by rainfall (Influence by medieval mountain castle ruins)
3. The analysis with cumulative grain size curve of medieval castle ruins dry moat soil
This study compared the two geology of Hiroshima granites (granite) and Takada rhyolite (rhyolite). These were accounted for 96.7% of landslides in the analysis area when the torrential rain in July 2018.
As shown in the geological distribution with Fig.1and Fig2, Analysis area (Higashi-Hiroshima City) and Kure City and Takehara City have a lot of granite area and medieval castle ruins on granite, and Akitakata City has a lot of those on rhyolite. As a result of Confirmation, only Akitakata City had few past landslides on survey sketch of ruins, in spite of there were many medieval castle ruins located in high places which has influence for landslide (Fig.3).
Comparing the collapse area ratio within the analysis area, it was found that granite area was more affected by artificial terrain change of the medieval mountain castle ruins than rhyolite area (Fig.4).
As the result of analysis by cumulative grain size curve for soil of the dry moat at the medieval mountain castle ruins, it was found from that the granite area was sandy and therefore high water-permeability than the silty rhyolite area (Fig.5).
In conclusion, the medieval mountain castle ruin in granite area was found to be at high risk of sediment disasters such as debris flow and landslides than that in rhyolite area.
The author indicated with the results of field work that the dry moat of medieval mountain castle ruins caused some landslides (Inomata, 2021, under review).
The purpose of this study was to investigate whether the risk of medieval mountain castle ruins is a region-specific risk. Therefore, that focused on the geology and analyzed the following three items.
1. Confirmation of past landslides on survey sketch of ruins
2. The ratio of collapse area by rainfall (Influence by medieval mountain castle ruins)
3. The analysis with cumulative grain size curve of medieval castle ruins dry moat soil
This study compared the two geology of Hiroshima granites (granite) and Takada rhyolite (rhyolite). These were accounted for 96.7% of landslides in the analysis area when the torrential rain in July 2018.
As shown in the geological distribution with Fig.1and Fig2, Analysis area (Higashi-Hiroshima City) and Kure City and Takehara City have a lot of granite area and medieval castle ruins on granite, and Akitakata City has a lot of those on rhyolite. As a result of Confirmation, only Akitakata City had few past landslides on survey sketch of ruins, in spite of there were many medieval castle ruins located in high places which has influence for landslide (Fig.3).
Comparing the collapse area ratio within the analysis area, it was found that granite area was more affected by artificial terrain change of the medieval mountain castle ruins than rhyolite area (Fig.4).
As the result of analysis by cumulative grain size curve for soil of the dry moat at the medieval mountain castle ruins, it was found from that the granite area was sandy and therefore high water-permeability than the silty rhyolite area (Fig.5).
In conclusion, the medieval mountain castle ruin in granite area was found to be at high risk of sediment disasters such as debris flow and landslides than that in rhyolite area.