The temporal and spatial scales of rocky coast geomorphology: a commentary

Rocky shores are complex landforms that result from marine erosion and subaerial weathering. They are time-integrated features where their present day form is the result of instantaneous erosion, often on the millimetre to sub-metre scale, occurring for centuries to millennia. As a result, research on rocky coasts focuses on a range of temporal and spatial scales from granular-scale swelling of a rock surface and instantaneous wave impact to modelling millennial-scale sea level drivers. The challenge for rocky coast researchers is either to upscale or to downscale their results to the human-timescales of greatest interest to managers. The research presented in Earth Surface Processes and Landforms over the past 3 years highlights the range of spatial and temporal approaches to the study of coastal cliffs and shore platforms. We identify a key temporal and spatial gap in current research. Seasonal–annual timeframes over hundreds of metres to kilometre scale studies appear to be lacking and are likely critical in understanding the future evolution of rocky coasts, especially their response to climate change

Weathering rates of sandstone in a semi-arid environment (Hunter Valley, Australia)

The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years. This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region. Of the four processes examined, only the freeze-thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region