Modelling the relative dominance of wave erosion and weathering processes in shore platform development in micro‐ to mega‐tidal settings

Abstract

In this paper we use a numerical model to explore the relative dominance of two main processes in shore platform development: wave erosion; weathering due to wetting and drying. The modelling approach differs from previous work in several aspects, including: the way that it accounts for weathering arising from gradual surficial intertidal rock degradation; subtidal profile shape development; and the consideration of a broad erosion parameter space in which, at either end of the erosion spectrum, shore platform profiles are produced by waves or weathering alone. Results show that in micro‐tidal settings, wave erosion dominates the evolution of (i) shore platforms that become largely subtidal and (ii) sub‐horizontal shore platforms that have a receding seaward edge. Weathering processes dominate the evolution of sub‐horizontal shore platforms with a stable seaward edge. In contrast, sloping shore platforms in mega‐tidal settings are produced across the full range of the process‐dominance spectrum depending on the how the erosional efficacy of wave erosion and weathering are parameterized. Morphological feedbacks control the process‐dominance. In small tidal environments wave processes are strongly controlled by the presence/absence of an abrupt seaward edge, but this influence is much smaller in large tidal environments due to larger water depths particularly at high tides. In large tidal environments, similar shore platform profile geometries can be produced by either wave‐dominant or weathering‐dominant process regimes. Equifinality in shore platform development has been noted in other studies, but mainly in the context of smaller‐scale (centimetre to metre) erosion features. Here we draw attention to geomorphic equifinality at the scale of the shore platform itself. Progress requires a greater understanding of the actual mechanics of the process regimes operating on shore platforms. However, this paper makes a substantial contribution to the debate by identifying the physical conditions that allow clear statements about process dominance. © 2018 John Wiley & Sons, Ltd.

Hard-Rock Coastal Modelling: Past Practice and Future Prospects in a Changing World

“…It is ironic, given the importance traditionally accorded to weathering in the rock coast literature, and the availability of much better data on surface downwearing (erosion in the vertical plane) than on wave-generated backwearing (erosion in the horizontal plane), that weathering has generally been neglected by rock coast modelers. Nevertheless, a few models have incorporated weathering and debris removal in a suite of erosional processes [37,[41][42][43][44], and others have treated it in isolation to determine whether it can produce shore platforms when acting alone [45][46][47]. Several semi-quantitative and numerical models have also been developed to consider episodic notch formation and cliff collapse, due to abrasion and weathering, followed by cliff collapse and debris removal [48][49][50][51][52].…”

“…This conclusion for sloping intertidal shore platforms in areas with moderate to high tidal range, supports the hypothesis put forth earlier by Dickson et al [73] for subhorizontal shore platforms in low tidal range environments. It emphasizes the need for weathering to be included in evolutionary models, and implies that erosional thresholds should be represented by time-dependent variables [37,47] rather than by constant values.…”

Biological Zonation and Bedrock Strength on a High Energy Granite Shore Platform

“…Rock surface hardness can help inform on the interactions between these external and intrinsic controls. Several previous studies show how mechanical erosion by waves can remove a weathered rock carapace, exposing harder rocks beneath (Matsumoto et al, 2018), and such removal and transport of large bedrock blocks has been described by Knight and Burningham (2011) on the Falchorrib-Trawenagh shoreline. Increased wave erosion around the position of HAT on flat shore platforms can result in higher Equotip values when compared to other positions higher or lower in the tidal frame (Knight and Burningham, 2019).…”

Erosion of rocky shore platforms by block detachment from layered stratigraphy

“…Focusing of rock decay and erosion at discontinuities play an important role in landscape development across terrestrial and coastal landscapes (Scott and Wohl, 2019). The meso-scale blocky processes documented throughout, now need to be included in numerical models of shore platform evolution (Matsumoto et al, 2018), similar to recent developments in the modelling of hillslope sediment transport (e.g. Glade et al, 2017).…”