Shore platform erosion and cliff retreat in the Eastern Korea: A quantified assessment using 10Be concentrations and numerical modeling

Shore platforms, essential for coastal analysis and management, are poorly understood in terms of their long-term evolution, particularly regarding coastal cliff retreat rates and trends, despite their common presence in rocky coastlines. Rock coasts constitute fully erosional environments, yet long-term rates and trends of coastal cliff retreat remain poorly understood. This study adds to the limited number of studies that use cosmogenic isotopes to reconstruct millennial-scale cliff erosion. Cosmogenic ¹⁰Be concentrations were measured in 16 rock samples collected across an active 31 m wide granitic Jangsa shore platform in eastern Korea. A geometry-based inverse numerical model was used to simulate ¹⁰Be concentrations for various cliff retreat modes, relative sea level curves, and platform downwearing models. The model results were combined with measured concentrations to find the most likely scenario for coastal evolution. Our findings reveal that the shore platform has widened through time and is entirely formed during the Holocene, unlike the previous cosmogenic study in western Korea that attributed the formation of shore platforms to former interglacial periods. The results suggest acceleration in cliff retreat rate from 1.4 mm yr⁻¹ at 7.4 kyr BP to 7.0 mm yr⁻¹ at present. Accelerating cliff erosion may pose a threat to coastal communities, particularly in the context of observed and predicted anthropogenic sea level rise.