Coastline retreat via progressive failure of rocky coastal cliffs

Abstract

. (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

Optimising 4-D surface change detection: an approach for capturing rockfall magnitude–frequency

“…Near-continuous TLS has the potential to generate a considerable number of point clouds (> 10 3 -10 4 ), representing a 2 to 3 order of magnitude increase in data volume over previous terrestrial lidar monitoring campaigns with lower temporal resolution (e.g. Teza et al, 2007;Abellán et al, 2010;Rosser et al, 2013;Royán et al, 2015). Key attributes of the techniques developed to process such datasets therefore relate to computational efficiency, the ability to automate processing, and minimising the accumulation of error between each survey pair.…”

Synthesis Study of an Erosion Hot Spot, Ocean Beach, California

“…Yellow areas have differences less than the overall change detection uncertainty of 60.5 m. Grey areas do not have data in the first of the two differenced point clouds. Difference maps are presented in the direction normal to the SfM-generated surface using the M3C2 methods of Lague, Brodu, and Leroux (2013) these changes (Emery and Kuhn, 1982;Hall et al, 2002;Hapke, Reid, and Richmond, 2009;Rosser et al, 2013;Sunamura, 1992;Trenhaile, 1987;Young et al, 2011). Topographic data are essential because they reveal patterns of cliff failure, talus erosion, and beach change, which can be used, in turn, to better understand the processes responsible for erosion of sea cliffs (e.g., Collins and Sitar, 2008;Hampton, 2002;Vann Jones et al, 2015;Young, 2015;Young et al, 2009).…”

“…Coastal change measurements are also useful as a basis to understand and to predict the response of coastal landforms to storms, climate, and sealevel change that will occur in the future (Cazenave and Cozannet, 2014;Cowell and Kench, 2001;Fitzgerald et al, 2008;Hapke and Plant, 2010;McGranahan, Balk, and Anderson, 2007). Several techniques are used to measure beach and sea-cliff changes, including topographic and bathymetric surveying (Larson and Kraus, 1994;Morton, Paine, and Gibeaut, 1994;Ruggiero et al, 2005), aerial or satellite-based imagery (Fletcher et al, 2003;Hapke and Richmond, 2000;White and El Asmar, 1999), light detection and ranging (LIDAR) from airborne or terrestrial platforms (Rosser et al, 2013;Sallenger et al, 2002;Stockton et al, 2002;Vann Jones et al, 2015;Young et al, 2010), and combinations of these techniques (Adams and Chandler, 2002;Ruggiero et al, 2013;Smith and Zarillo, 1990).…”

Cliff Collapse Hazard From Repeated Multicopter Uav Acquisitions: Return on Experience

“…In the last decade, advances in rock fall hazards has widely benefitted from the topographic measurement capacity of Terrestrial Laser Scanners (Abellán et al, 2010;Dewez and Rohmer, 2013;Rosser et al, 2014). When surveys are repeated at regular time intervals of a few weeks or months on a cliff face, topographic changes reveal the scars of rock falls.…”