. 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.

/pdf/globr2c2-global-recession-rates-of-coastal-cliffs-a-global-5bo3rul5kb.pdf

GlobR2C2 (Global Recession Rates of Coastal Cliffs): a global relational database to investigate coastal rocky cliff erosion rate variations

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 ...

https://bioone.org/journals/journal-of-coastal-research/volume-65/issue-sp2/SI65-286.1/Coastal-chalk-platform-erosion-modulated-by-step-erosion-and-debris/10.2112/SI65-286.1.pdf

Coastal chalk platform erosion modulated by step erosion and debris shielding: example from Normandy and Picardy (northern France)

https://hal-insu.archives-ouvertes.fr/insu-01366304/document

Pleistocene uplift, climate and morphological segmentation of the Northern Chile coasts (24°S–32°S): Insights from cosmogenic 10Be dating of paleoshorelines

Most of the Earth coasts recedes and 80 % are rocky. Prediction of sea-cliff recession is essential to anticipate future risks for coastal development. However, it is difficult to understand this recession because many parameters control it. In addition, both the space and time scales are too big for the different mechanisms of cliff erosion to be fully analysed. Experiments in a small-scale wave flume were conducted in which a massif made of wet sand is submitted to wave attack. The aim is to understand how cliff erosion is wave-controlled. The technique of shadow graph measurements was used to detect the time evolution of sand and water surfaces. We have analyzed the influence of wave forcing (F , ξ) (where F is the incident offshore wave energy flux and ξ is the surf similarity parameter) on the cliff recession rate and on collapse event size. The cliff recession rate increases linearly with the wave energy flux F . The eroded cliff materials change the bottom morphology ; the types of bottom morphology strongly depend on the surf similarity parameter at the breaker point, or the Dean parameter Ω. Bottom profiles characterized by unsteady self-sustained sandbar oscillation were observed. In addition, we studied how sand granulometry change the system evolution. Finer the sand is, more cohesive is the cliff and bigger are cliff collapses. Contrary to what was expected, cliff recession is more important for a finer sand : this could be due to a more dissipative bottom morphology built by fine sands. The sand volume within the system changes following cliff collapses and a sandbar removal during particular experiments. The cliff recession rate is constant when the sandbar is removed and decreases with cliff height. It seems that the unsteadiness of the bottom profile is activated when the volume of eroded sand exceeds a threshold value.

Présentée et soutenue par

Elevations of the shoreline angles of marine terraces have long been used to infer Pleistocene sea levels and/or uplift rates. We attempt to use morphologic properties of sequences of marine terraces-terrace width and slope-in order to track if these constitute a pattern showing similar alternations at different sites and if this alternation is comparable to the signal from the sea level highstand succession –duration and sea level-for Middle-Late Pleistocene. To do so, we focus on sequences of marine terrace including more than 10 successive strandlines from San Clemente Island and Santa Cruz (both in California, USA). We generated and analyzed 30 topographic profiles in order to confirm the occurrence or lack of each terrace, and to characterize their width and slope. To complement the observation of tenuous trends, we used additional data from previous works at Point Reyes (California, USA), Altos de Talinay (central Chile), San Juan de Marcona (central Peru) and South Taranaki (Northern Island, New Zealand). These additional data strengthen the observations made at San Clemente and Santa Cruz and prove that the most prominent terrace observed is usually carved during the Marine Isotopic Stage 5 (MIS5). Moreover, some terraces appear better expressed than the others: those formed during MIS7, MIS9 plus one of those formed during MIS15, MIS17 or MIS19 highstands. The terraces formed during MIS11 are not preeminent, contrary to what expected from its long highstand duration.

/pdf/geometrical-trends-within-sequences-of-pleistocene-marine-3qoivqimhv.pdf

Geometrical trends within sequences of Pleistocene marine terraces : selected examples from California, Peru, Chile and New-Zealand

Cliff retreat and sea bed morphology under monochromatic wave forcing: Experimental study

Laboratory experiments have been performed in a wave flume to investigate the coastal cliff recession under regular waves forcing. The different processes of the cliff erosion cycle are described and we focus on bottom evolution, which seem mostly depend on the surf similarity parameter ξ. We observed steep planar (ξ > 0.7), gentle planar (0.5 < ξ < 0.7) and bared (ξ < 0.5) profiles. We noticed different sandbar dynamics including either steady or unsteady self-sustained oscillating states. Then we estimate the role of the self-organized material on the cliff recession rate. We show that the cliff erosion increases with the wave energy flux and is stronger for a gentle planar profile than for a bared profile of bottom morphology. However, the cliff recession rate as a function of the cliff height is not monotonic due to a different dynamics of bottom morphologies.

/pdf/experimental-analysis-of-erosive-cohesive-coastline-1vsvo6nmyg.pdf

Experimental analysis of erosive cohesive coastline morphology

<0.7) and bared ( <0.5) proﬁles are observed. We different bar dynamics, including steady and unsteady self-sustained oscillatingstates. Then we analyzethe role of theerodedmaterial onthe cliffrecession rate. We showthat thecliffrecessionrateincreaseswiththewaveenergyﬂux.Moreover,foragivenwave ﬂux, itislarger foragentleplanarproﬁlethan baredproﬁle.However similarboth abaredproﬁleand steepplanarproﬁle.Thecliffrecessionrateisnot monotonicfunction ofthecliffheightasthetypeofbottomproﬁleinﬂuencesthewaveenergyatthecliff. 2011 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.

https://oatao.univ-toulouse.fr/10167/1/Caplain_10167.pdf

Cliff retreat and sea bed morphology under monochromatic wave forcing: Experimental study Recul de falaise et morphologie du fond sableux sous un forcage de houle monochromatique : etude experimentale

Laboratory experiments were carried out in a monochromatic wave flume. Natural coarse sands are used t o represent cliff erosion and bottom morphodynamics with a reasonable time scale. A bottom typology is established as a function of wave forcing, through the wave energy flux F and the surf similarity parameter ξ. The bottom types strongly depend on the surf similarity parameter at the breaker poi nt ξb. Steep terraces ( ξb > 0.48), one-bar profiles (0.42 < ξb < 0.48), gentle terraces (0.38 < ξb < 0.43) and double-bars profiles ( ξb < 0.38) were observed. Sediment grain diameter change /

Cliff erosion and bottom morphodynamics in a wave flume

. Laboratory experiments on cliﬀ erosion were carried out in a monochromaticwave ﬂume. Natural coarse sands are used to represent cliﬀ erosion and bottom mor-phodynamics with a reasonable time scale. A bottom typology is established as a func-tion of wave forcing, through the wave energy ﬂux F and the surf similarity parameterξ. The bottom types strongly depends on the surf similarity parameter at the breakerpoint ξ b . Steep terraces (ξ b > 0.48), one-bar proﬁles (0.42 < ξ b < 0.48), gentle ter-races (0.38 < ξ b < 0.43) and double-bars proﬁles (ξ b < 0.38) were observed. It can betranslated into a Dean parameter Ω vs. Shields number Θ b space to take into accountsediment granulometry. Sediment grain diameter change has no noticeable inﬂuence onbottom typology. The bottom types depends more on the Dean parameter Ω than onthe Shields number Θ b . Finally, we explored cliﬀ height eﬀect: it does not modify thebottom typology established. 1. Introduction Predicting the coastline evolution depends on the geo-logical nature of the coastline. Natural coastal areas maybe composed of sand, silt, mangroves or rocks, as cliﬀs.Rocky shores occupy about 80% of the coastline of the Earth[Emery and Kuhn, 1980]. This contribution aims at bringn-ing new informations on how such kind of coasts behave.Rocky shores, also known as cliﬀed coasts are usuallycomposed of a platform (’wave cut platform’) backed by acliﬀ [e.g., Sunamura, 1992]. Cliﬀ erosion is mainly con-trolled by wave impact but depends likewise on numerousfactors [Sunamura, 1992], such as weathering by wettingand drying cycles during tidal cycles [Kanyaya and Tren-haile, 2005], rainfall [Duperret et al., 2002; Costa et al., 2004;Young et al., 2009], bioerosion [e.g., Nesteroﬀ and M´eli`eres,1967; Andrews and Williams, 2000], material stratiﬁcationor fractures [Duperret et al., 2004]. Moreover, the character-istic scales of cliﬀ erosion are very large, encompassing thesingle wave scale or a kilometers-long retreat on geologicaltimes (thousands to millions of years). Here we take theadvantage of using a physical model to simplify the analysisof rocky shore retreat, in order to analyze accurately eachmechanism.If the wave height and the cliﬀ height are the same or-der, waves can reach and erode the cliﬀ top ([Hansom et al.,2008]). We limited our study to the inﬂuence of wave forc-ing on the cliﬀ erosion by undermining, i.e., when the waveheight is less than the cliﬀ height. Cliﬀ erosion by undermin-ing is the result of a series of cycles, each one correspondingto 3 successive phases:• Phase 1: cliﬀ toe erosionThe mechanical action of impacting waves cut the cliﬀ toecreating a notch, as the forces resulting from the impact can

Bastien Caplain

Papers

Cliff retreat and sea bed morphology under monochromatic wave forcing: Experimental study

Experimental analysis of erosive cohesive coastline morphology

Cliff retreat and sea bed morphology under monochromatic wave forcing: Experimental study Recul de falaise et morphologie du fond sableux sous un forcage de houle monochromatique : etude experimentale

Cliff erosion and bottom morphodynamics in a wave flume

eroded by monochromatic waves