Threshold height of coastal cliffs for collapse due to tsunami: Theoretical analysis of the coral limestone cliffs of the Ryukyu Islands, Japan

Modeling boulder transport by coastal waves on cliff topography: Case study at Hachijo Island, Japan

“…This is because the rocks with several meters of notch depth had likely been already detached from the cliff due to wave erosion and deposited as boulders. The process by which a boulder is detached from the cliff is not included in our simulation; in order to calculate this process, the empirical equation proposed by Kogure and Matsukura () or the beam equation proposed by Herterich et al () should be used.…”

“…This is because the rocks with several meters of notch depth had likely been already detached from the cliff due to wave erosion and deposited as boulders. The process by which a boulder is detached from the cliff is not included in our simulation; in order to calculate this process, the empirical equation proposed by Kogure and Matsukura (2012) Our calculation predicted that the boulders would be distributed in a wide range in the case of tsunami forcing (Figure 12b). In fact, both large and small boulders are deposited in a narrow range (0~90 m inland from the shoreline) in our study site.…”

“…Although cliff‐top boulder research has been mainly conducted based on field surveys, the hydraulic force necessary to transport boulder onto a cliff‐top can be examined with theoretical or numerical modelling, and by conducting laboratory experiments (e.g., Noormets et al, ; Hansom et al, ; Kogure and Matsuoka, ; Rovere et al, ; Herterich et al, ). For the calculation of cliff‐top deposition from either the cliff edge or the cliff base, the vertical boulder transport motion must be solved because the vertical acceleration (leading to vertical wave force) becomes significant in these locations (Noormets et al, ).…”