Rocky coast erosion (i.e., cliff retreat) is caused by a complex interaction of various forcings that can be marine, subaerial or due to rock mass properties. From Sunamura's seminal work in 1992, it is known that cliff retreat rates are highly variable over at least four orders of magnitude, from 1 to 10 mm yr⁻¹. While numerous local studies exist and explain erosion processes at specific sites, there is a lack of knowledge at the global scale. In order to quantify and rank the various parameters influencing erosion rates, we compiled existing local studies into a global database called GlobR2C2 (which stands for Global Recession Rates of Coastal Cliffs). This database reports erosion rates from publications, cliff setting and measurement specifications; it is compiled from peer-reviewed articles and national databases. In order to be homogeneous, marine and climatic forcings were recorded from global models and reanalyses. Currently, GlobR2C2 contains 58 publications that represent 1530 studied cliffs and more than 1680 estimated erosion rate. A statistical analysis was conducted on this database to explore the links between erosion rates and forcings at a global scale. Rock resistance, inferred using the criterion of Hoek and Brown (1997), is the strongest signal explaining variation in erosion rate. Median erosion rates are 2.9 cm yr⁻¹ for hard rocks, 10 cm yr⁻¹ for medium rocks and 23 cm yr⁻¹ for weak rocks. Concerning climate, only the number of frost days (number of day per year below 0 °C) for weak rocks shows a significant, positive, trend with erosion rate. The other climatic and marine forcings do not show any clear or significant relationship with cliff retreat rate. In this first version, GlobR2C2, with its current encompassing vision, has broad implications. Critical knowledge gaps have come to light and prompt a new coastal rocky shore research agenda. Further study of these questions is paramount if we one day hope to answer questions such as what the coastal rocky shore response to sea-level rise or increased storminess may be.

Dewez, T.J.B., Rohmer, J., Regard, V., and Cnudde, C., 2013, Probabilistic coastal cliff collapse hazard from repeated terrestrial laser surveys: case study from Mesnil Val (Normandy, northern France) Along cliff edges, coastal managers dealing with life-safety matters often wonder “how much time have I got left before I need to expropriate this house?” Here, we present a case study where repeated terrestrial laser scanner surveys (TLS) were performed to monitor a chalk cliff section in Normandy. The Mesnil Val cliff, cut in Upper Cretaceous chalk known as the Upper Lewes Nodular Chalk, is a ca. 750-m-long, 20–80m-high cliff section. It was surveyed 6 times between December 2005 and March 2008 at a 1 –point-per-5cm resolution. Successive Digital Surface Models (DSM) of the cliff surface were subtracted to reveal the location and shape of erosion scars. Scars detection relies on a robust indicator of observed noise distribution. The resulting scar inventory contains more than 8500 objects with vol...

Underground cavities are ubiquitous across northern Europe's cities and countryside due to a long history of mining and building‐stone extraction. Management of cavity‐collapse risks requires detailed knowledge of a cavity's geometry, depth and rock‐mass characterisation. Current mapping practices are neither sufficiently accurate, detailed nor cost‐effective in underground settings. Here, a GeoSLAM Zeb‐Revo handheld mobile laser scanner was tested. Its point clouds reproduced planes faithfully (RMS < 10 mm) over typical gallery dimensions (<10 m) and any survey horizontality defect was not measurable. In well‐structured corridor networks, reference distance inaccuracy arising after a 115 m loop and 5·25 minutes of instrumental drift did not exceed 3 mm over 30 m (1:10 000) and the difference from the reference length was insignificant. Applied to mapping 11 ha of a disused underground stone quarry in the Paris Basin, Zeb‐Revo surveys produced accurate (<1 m) base maps adequate for regulatory cavity hazard maps at 1/5000 scale. Geometric knowledge of accessible cavities is therefore no longer a challenge for collapse hazard mapping.

Rohmer, J., Dewez, T., 2013. On the deviation of extreme sea-cliff instabilities from the power-law frequency-volume distribution: practical implications for coastal management. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1698–1703, ISSN 0749-0208.--> Predicting very large sea cliff instabilities (extremes) are of primary importance for coastal risk management. Numerous works have addressed this problem based on the same paradigm: if events exhibit the same statistical properties across a broad range of sizes, the probability of very large extreme events can be evaluated by extrapolating the frequency-size distribution (traditionally represented by a power law model). We address this issue with an inventory of >8,500 sea cliff failures collated from repeated terrestrial laser scanning (TLS) surveys along a coastal chalk cliff in Normandy (France)...

Regard, V., Dewez, T., Cnudde, C. and Hourizadeh, N., 2013. Coastal chalk platform erosion modulated by step erosion and debris shielding: example from Normandy and Picardy (northern France) Coastal platforms and cliffs compose an inter-dependant dynamic system. To understand how cliffed coast evolve, it is therefore crucial to quantify the magnitude and dependence of their processes. Here we question the role of erosion by waves at platform steps, often linked to lithological discontinuities. Along the French chalky coast of the English Channel, we determine, by comparison of aerial photographs at 23 yr interval that the mesoscale steps are retreating at a rate of ~2 cm/yr, ca. 10% cliff retreat rate. This corresponds to an average erosion rate of 0.32 ± 0.08 mm/a, quite uniform across the study area, suggesting that the geology has more of a control on erosion processes than the position in the tidal frame. In reality, erosion occurs only where platform surface is not shielded by debris fallen ...