The rock coast of Japan
The Japanese islands, situated in a tectonically unstable region with a highly variable geology, are exposed to high wave energy and microtidal environments in most locations. Rocky coasts are common, most having a steep cliff with coastal recession being primarily driven by wave erosion. A fundamental relationship between recession and wave force is obtained through reanalysis of previous laboratory data. On the basis of this relation a model is constructed for the development of type B platforms, that is, horizontal or subhorizontal platforms that have a steep scarp at the seaward edge. The process of wave attenuation on this type of platform and weathering-induced strength reduction of rocks are incorporated into the model. The model is applied to the southwestern coast of the Kii Peninsula and a platform at Ebisu-jima of the Izu Peninsula. Long-term development rates of platforms in the former area are examined: the model indicates that the rate of erosion when platforms were initiated at 6000 years BP is two orders of magnitude greater than present. At the Ebisu-jima platform, wave-induced erosion processes are explored on a daily basis: the model provides a description of temporal variations in platform growth, although the result is not fully satisfactory.
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Figures & Tables
Rocky landforms dominate large portions of the world's coast. Cliffs and shore platforms form spectacular landscapes, yet when compared to other landforms they are relatively unstudied with many contemporary controversies dating back to the mid-nineteenth century. The past decade has seen a reinvigoration of research driven by advances in technology that now enable precise measurements of erosion to the micron scale and quantification of wave energy onto and through cliff edifices to be made, as well as being able to directly date rock surfaces. In order to integrate this diverse range of research this volume's regional approach first integrates the latest data with longstanding theory and then analyses this research through the boundary conditions that exist in each area. The volume brings together the research leaders in the field; includes chapters on nearly all the major rock coasts of the world and identifies future research needs.