Multi‐annual variability of storm events and morphological response in the SW Iceland: The Valahnúkamöl boulder barrier

While many studies have highlighted the high mobility of gravel/pebble beaches due to storm waves, further research is needed to improve understanding of the morphodynamic of coastal boulder accumulations. This paper provides original data about storm‐induced morphogenetic processes for the Valahnúkamöl boulder barrier located in the Reykjanes Peninsula (SW Iceland). The study is based on annual topo‐morphological surveys conducted from 2015 to 2023 and a shoreline change analysis for the period 1978–2023 using a series of aerial photos. In addition, hydrodynamic conditions (wave and water levels) were analysed using field records and model results. Results show a good correspondence of the morphological changes of the barrier to the frequency/energy of morphogenetic events. Interannual surveys (2015–2023) indicate a high mobility of boulders across the beachface regardless of the variability of hydrodynamic conditions. In contrast, boulders located on the crest and the back‐barrier moved more episodically by overtopping and overwashing processes during extreme events combining storm waves and high spring tide levels. A massive landward transfer of boulders resulting in the most significant barrier retreat, −6.1 m, was recorded during the winter 2022. Between 1978 and 2023, the mesoscale shoreline changes of the barrier retreated landward by rollover. The pluri‐decadal variability in shoreline retreat rates seemed to be strongly controlled by extreme hydrodynamic conditions. However, this cross‐shore dynamic responses to episodic overwash depended on specific geological constraints. This survey provides a first quantitative assessment of the morphological impact of significant morphogenetic events within the highly energetic hydrodynamic context of SW Iceland. These data complement surveys undergone through a wide range of coastal morphologies elsewhere along the Western coasts of the North Atlantic basin. Such assessments may prove useful in anticipating the potential intensification of hydrodynamic conditions at mid‐latitudes due to climate change.