Storm-induced erosion and shoreline retreat of barrier islands are assumed to be primarily controlled by the intensity of the hydrodynamic forcing and barrier morphology. However, less studied non-dynamic variables such as the underlying bedrock topography can mediate the morphological response in geologically controlled barrier systems. This work investigates the role of geological control on barrier island morphodynamics during an extreme storm event. Exposed to highly energetic wave conditions in the West of Scotland, a unique barrier island system developed over a gentle sloping bedrock surface along the Outer Hebrides. Morphological changes driven by an extreme storm in February 2022 were monitored along sections of the Hebridean barriers, revealing muted morphological storm response, but with alongshore variable storm impacts. These ranged from minor dune erosion to overwash of low-lying composite barriers and are linked to variation in barrier morphology and the slope of the bedrock-controlled shoreface and intertidal terrace, which strongly influence nearshore wave transformation. Results suggest that severe storm impacts in the Outer Hebrides barrier islands are only observed when there is an exceptional combination of hydrodynamic forcing (extreme storm waves with high tides and storm surges) and will be enhanced in areas with lower dune morphology and narrower geologically controlled intertidal terraces. Nearshore hydrodynamic processes such as surf beat and wave setup are likely to be important to understand morphological changes in such underreported geologically controlled barrier systems.
