Sea-cliff retreat and shore platform widening: steady-state equilibrium?

We challenge the notion of steady-state equilibrium in the context of progressive cliff retreat on micro-tidal coasts. Ocean waves break at or close to the abrupt seaward edge of near-horizontal shore platforms and then rapidly lose height due to turbulence and friction. Conceptual models assume that wave height decays exponentially with distance from the platform edge, and that the platform edge does not erode under stable sea-level. These assumptions combine to a steady-state view of Holocene cliff retreat. We argue that this model is not generally applicable. Recent data show that: (1) exponential decay in wave height is not the most appropriate conceptual model of wave decay; (2) by solely considering wave energy at gravity wave frequencies the steady-state model neglects a possible formative role for infragravity waves. Here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances (and longer timescales) than imaginable under the established conceptual model. Copyright (c) 2013 John Wiley & Sons, Ltd.