@article{fdi:010082736, title = {{C}onceptual model of fracture-limited sea cliff erosion : erosion of the seaward tilted flyschs of {S}ocoa, {B}asque {C}ountry, {F}rance}, author = {{P}remaillon, {M}. and {D}ewez, {T}. {J}. {B}. and {R}egard, {V}. and {R}osser, {N}. {J}. and {C}arretier, {S}{\'e}bastien and {G}uillen, {L}.}, editor = {}, language = {{ENG}}, abstract = {{S}ea cliff morphology and erosion rates are modulated by several factors, including rock control that reflects both lithology and rock structure. {E}rosion is anticipated to preferentially exploit 'fractures', broadly meant as any discontinuity in an otherwise continuous medium, where the rock mass is weakest. {U}npicking the direct control of such fractures on the spatial and temporal pattern of erosion remains, however, challenging. {T}o analyse how such fractures control erosion, we monitored the evolution of a 400 m-long stretch of highly structured sedimentary cliffs in {S}ocoa, {B}asque {C}ountry, {F}rance. {T}he rock is known as the {S}ocoa flysch formation. {T}his formation combines decimetre-thick turbidites composed of repeat triplets of medium to strong calcareous sandstone, laminated siltstones and argillaceous marls. {T}he sequence plunges at 45 degrees into the sea with a shore-parallel strike. {T}he cliffs are cross-cut by two normal and reverse fault families, with 10-100 m alongshore spacing, with primary and secondary strata-bound fractures perpendicular to the bedding, which combined delimit the cliff rock mass into discrete blocks that are exploited by the erosion process. {E}rosion, and sometimes plucking, of such beds and blocks on the cliff face was monitored using ground-based structure-from-motion ({S}f{M}) photogrammetry, over the course of 5.7 years between 2011 and 2017. {T}o compare with longer time change, cliff-top retreat rate was assessed using {S}f{M}-orthorectified archive aerial photographs spanning 1954-2008. {W}e show that the 13,250 m(2) cliff face released 4500 blocks exceeding 1.45 x 10(-3) m(3), removing a total volume of 170 m(3). {T}his equates to an average cliff erosion rate of 3.4 mm/year, which is slightly slower than the 54-year-long local cliff-top retreat (10.8 +/- 1.8 mm/year). {T}he vertical distribution of erosion reflects the height of sea water inundation, where the maximum erosion intensity occurs ca. 2 m above high spring-tide water level. {A}longshore, the distribution of rockfall scars is concentrated along bed edges bounding cross-cutting faults; the extent of block detachment is controlled by secondary tectonic joints, which may extend through several beds locally sharing similar mechanical strength; and rockfall depth is always a multiple of bed thickness. {O}ver the longer term, we explain block detachment and resultant cliff collapse as a cycle. {E}rosion nucleates on readily exploitable fractures but elsewhere, the sea only meets defect-free medium-strong to strong rock slabs offering few morphological features for exploitation. {S}tructurally delimited blocks are quarried, and with sufficient time, carve semi-elliptic scars reaching progressively deeper strata to be eroded. {L}ateral propagation of erosion is directed along mechanical weaknesses in the bedding, and large episodic collapses affect the overhanging slabs via sliding on the weak marl beds. {C}ollapse geometry is confined to one or several triplets of turbidite beds, but never reaches deeper into the cliff than the eroded depth at the foot. {W}e contend that this fracture-limited model of sea-cliff erosion, inferred from the {S}ocoa site dynamics and its peculiar sets of fractures, applies more broadly to other fractured cliff contexts, albeit with site-specific geometries. {T}he initiation of erosion, the propagation of incremental block release and the ultimate full failure of the cliff, have each been shown to be fundamentally directly controlled by structure, which remains a vital control in understanding how cliffed coasts have changed in the past and will change in the future.}, keywords = {{B}asque {C}ountry ; discontinuities ; erosion ; flysch ; photogrammetry ; plucking ; sea cliff ; {S}f{M} ; {FRANCE} ; {PAYS} {BASQUE} ; {SOCOA}}, booktitle = {}, journal = {{E}arth {S}urface {P}rocesses and {L}andforms}, volume = {46}, numero = {13}, pages = {2690--2709}, ISSN = {0197-9337}, year = {2021}, DOI = {10.1002/esp.5201}, URL = {https://www.documentation.ird.fr/hor/fdi:010082736}, }