We report a series of short-term (diurnal) rock surface monitoring studies on inter-and supra-tidal shore platforms using a traversing micro-erosion meter at two sites, Kaikoura Peninsula, New Zealand, and Apollo Bay, Victoria, Australia. Statistically significant day-to-day changes were measured. Surface rise and lowering occurred at rates above instrument error, with a maximum range of 3·378 mm between 1·697 mm (lowering) and −1·681 mm (rise). Individual measurements showed rises greater than 2 mm. These daily variations reveal that surface lowering and rise occur at a much shorter time scale than previously reported from other studies. The patterns observed suggest wetting and drying is the most likely process causing surface changes at these temporal scales. We argue that traversing micro-erosion meter studies operating at a short-term time scale of day-to-day provide meaningful results that open new opportunities for studying rock weathering and erosion in a coastal environment.

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.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.

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