Cliff-top boulder morphodynamics on the high–energy volcanic rocky coast of the Reykjanes Peninsula (SW Iceland)

Cliff-top boulder deposits (CBDs) are morphological indicators of high-energy conditions. Since 2014, a monitoring CBDs dynamics has been undertaken on the south-western coast Iceland (Reykjanes Peninsula) to monitor their long-term activation (quarrying, transport and deposition) as proxy inter-annual winter storminess variations basaltic cliff erosion processes in context rocky progradation. Annual topomorphological surveys four study sites were conducted Structure-from-Motion photogrammetry was performed quantify displacements. Hydrodynamic conditions analyzed based offshore waves water level. Results show that occurs every winter, regardless variability hydrodynamic Depending site year, >2% 17% accumulated above 8 m 10 asl at top cliffs regularly mobilized. While inland movements represent main mode blocks (between 50% 60%), seaward longshore also well represented (10% 20%). Longshore displacement is favored by wide tabular morpho-structural setting wave-scour cliff-top platforms, which explained structure pāhoehoe lava flows. The –measured from volumes displaced boulders–, shows good correspondence with frequency duration storms. However, case during 2018–2019, it rather intensity two highly morphogenic episodes combining storm especially very high spring tide levels, generated largest boulders Substantial interannual confirms they constitute an important still understudied system coasts, whose dynamic terms carrying, transport, deposition, could significantly increase rising sea