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. (2013) 'Coastline retreat via progressive failure of rocky coastal clis. ', Geology, 41 (8). pp. 939-942. Further information on publisher's website:http://dx.doi.org/10.1130/G34371.1Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Despite much research on the myriad processes that erode rocky coastal cliffs, accurately 7 predicting the nature, location and timing of coastline retreat remains challenging, confounded 8 by the apparently episodic nature of cliff failure. The dominant drivers of coastal erosion, marine 9 and sub-aerial forcing, are anticipated in future to increase, so understanding their present and 10 combined efficacy is fundamental to improving predictions of coastline retreat. We capture 11 change using repeat laser scanning across 2.7 x 10 4 m 2 of near-vertical rock cliffs on the UK 12 North Sea coast over 7 years to determine the controls on the rates, patterns and mechanisms of 13 erosion. For the first time we document that progressive upward propagation of failure dictates 14 the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline 15 above; notably a failure mechanism not conventionally considered in cliff stability models. 16Propagation of instability and failure operates at these sites at 10 1 year timescales and is 17 moderated by local rock mass strength and the time-dependence of rock fracture. We suggest 18 that once initiated, failure propagation can operate ostensibly independently to external 19 environmental forcing, and so may not be tightly coupled to prevailing subaerial and 20 oceanographic conditions. Our observations apply to coasts of both uniform and complex 21 lithology, where failure geometry is defined by rock mass strength and structure, and not intact 22 rock strength alone, and where retreat occurs via any mode other than full cliff collapse. 23

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract 5 This paper considers the role that microseismic ground displacements may play in fracturing 6 rock via cyclic loading and subcritical crack growth. Using a coastal rock cliff as a case 7 study, we firstly undertake a literature review to define the spatial locations that may be prone 8 to microseismic damage. It is suggested that microseismic weakening of rock can only occur 9 in 'damage accumulation zones' of limited spatial extent. Stress concentrations resulting from 10 cliff height, slope angle and surface morphology may nucleate and propagate a sufficiently 11 dense population of microcracks that can then be exploited by microseismic cyclic loading. 12We subsequently examine a 32-day microseismic dataset obtained from a coastal cliff-top 13 location at Staithes, UK. The dataset demonstrates that microseismic ground displacements 14 display low peak amplitudes that are punctuated by periods of greater displacement during 15 storm conditions. Microseismic displacements generally display limited preferential 16 directivity, though we observe rarely occurring sustained ground motions with a cliff-normal 17 component during storm events. High magnitude displacements and infrequently experienced 18 ground motion directions may be more damaging than the more frequently occurring, 19 reduced magnitude displacements characteristic of periods of relative quiescence. As high 20 magnitude, low frequency events exceed and then increase the damage threshold, these 21 extremes may also render intervening, reduced magnitude microseismic displacements 22 ineffective in terms of damage accumulation as a result of crack tip blunting and the 23 2 generation of residual compressive stresses that close microcracks. We contend that damage 24 resulting from microseismic ground motion may be episodic, rather than being continuous 25 and in (quasi-)proportional and cumulative response to environmental forcing. A conceptual 26 model is proposed that describes when and where microseismic ground motions can operate 27 effectively. We hypothesise that there are significant spatial and temporal limitations on 28 effective microseismic damage accumulation, such that the net efficacy of microseismic 29 ground motions in preparing rock for fracture, and hence in enhancing erosion, may be 30 considerably lower than previously suggested in locations where high magnitude 31 displacements punctuate 'standard' displacement conditions. Determining and measuring the 32 exact effects of microseismic ground disp...

[1] A two-year dataset of coastal cliff microseismic ground motions is used to explore energy transfer to a cliff. The long-term dataset enables us to characterise cliff motion responses to a wide range of environmental processes and examine whether short-term characteristics are representative of the long-term. We examine whether cliff-top motions are reliable proxies for environmental processes to inform future investigations into the drivers of erosion. The study is based at an actively eroding, macrotidal, hard rock cliffed coast where considerable intra-annual variability in wave, tide, and storm conditions permit the examination of a full range of environmental permutations. Three frequency bands of ground motion are identified that represent wind and wave processes that transfer energy to the cliff. Examining mean energy transfer by aggregating the frequency bands by sea water elevation reveals a notable departure from tidal inundation duration alone, of relevance to understanding the timing, duration and intensity of effective processes of erosion. Peak energy transfer to the cliff face occurs during the largest storms where water levels significantly exceed those of tidal inundation rather than at locations most frequently inundated by tides. We anticipate it is therefore these conditions that are likely to be most effective in eroding hard rock coasts, rather than periods which accrue energy transfer associated with still or calm waters, and hence tidally modulated inundation may not relate well to coastal erosion. Promisingly, despite signal overlap and noise, cliff-top motions can be used as proxies for the processes that transfer energy to the coast.