![]() ![]() As wind continuously blows over a body of water, it creates disturbances that transfer energy from the wind to the water which then propagates outwards from the point of generation in the form of gravity waves (Conley, 2015). Substantial interannual activation of the CBDs confirms that they constitute an important and still understudied proxy of the morphogenic system of high-energy rocky coasts, whose the dynamic in terms of carrying, transport, and deposition, could significantly increase with rising sea level. However, as was the case during the winter of 2018–2019, it was rather the intensity of two highly morphogenic episodes combining storm waves and especially very high spring tide water levels, that generated the largest boulders displacements. The activation of CBDs –measured from the volumes of displaced boulders–, shows a good correspondence with the frequency and duration of storms. Longshore displacement is favored by the wide tabular morpho-structural setting of the wave-scour cliff-top platforms, which is explained by the structure of pāhoehoe lava flows. ![]() While inland movements represent the main mode of transport of blocks (between 50% to 60%), seaward and longshore movements are also well represented (10% to 20%). Depending on the site and the year, >2% and 17% of the CBDs accumulated above 8 m to 10 m asl at the top of the cliffs are regularly mobilized. Results show that CBDs activation occurs every winter, regardless of the variability of hydrodynamic conditions. ![]() Hydrodynamic conditions were analyzed based on offshore waves and water level. Annual topomorphological surveys of four study sites were conducted and Structure-from-Motion photogrammetry was performed to quantify CBDs displacements. Since 2014, a monitoring of CBDs dynamics has been undertaken on the south-western coast of Iceland (Reykjanes Peninsula) to monitor their long-term activation (quarrying, transport and deposition) as a proxy of the inter-annual winter storminess variations and basaltic cliff erosion processes in a context of rocky coast progradation. We expect this model to have utility in many areas of the coastal sciences and engineering, including developing holistic response models, quantifying erosion potential at other locations, and managing coastal ecosystems.Ĭliff-top boulder deposits (CBDs) are morphological indicators of high-energy conditions. Finally, comparative analyses using wave power as a storm index shows CSII can capture decadal or seasonal scale storminess. Additionally, the CSII model uncovered a trend-not detectable by single storm impact analyses-toward greater storm impacts, which began c. Applying this model to long‐term water‐level data from a Virginia tide gauge showed that the greatest storm impact resulted not from the larger individual storms, such as the Ash Wednesday nor'easter of 1962, the “Perfect Storm” of 1991, or Hurricane Sandy of 2012, but rather from especially stormy winter seasons that occurred during the twenty‐first century. The new model utilizes user‐defined storm data to incorporate both individual storm magnitude and the cumulative effect of successive storms into an index, which is a proxy for beach erosion at a given time. This paper presents a new empirical model, called the cumulative storm impact index (CSII), that quantifies the impact of coastal storms on sandy beaches. ![]()
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