Clast abrasion of a rock shore platform on the Atlantic coast of Ireland

Abstract

AbstractThe abrasion of coastal rock platforms by individual or clusters of clasts during transport has not been quantitatively assessed. We present a study which identifies the types of abrasion and quantifies erosion due to the transport of clasts during three storms in February and March 2016. We explore relationships between platform roughness, determined by the fractal dimension (D) of the topographic profiles, geomorphic controls and the type and frequency of abrasion feature observed. Clast transport experiments were undertaken in conjunction with the measurement of wave energy to assess transport dynamics under summer and winter (non‐storm) conditions.Platform abrasion occurred extensively during the storms. We identify two types of clast abrasion trails: simple and complex. In addition, we find two forms of erosion occur on these trails: Scratch marks and Percussion marks. An estimated 13.6 m2 of the platform surface was eroded by clast abrasion on simple abrasion trails during the three storms. We attribute approximately two thirds of this to scratch‐type abrasion. The total volume of material removed by abrasion was 67 808 cm3. Despite the larger surface area affected by scratch marks, we find that the volume of material removed through percussion impact was almost seven times greater. We also find that the type and frequency of abrasion features is strongly influenced by the effect of platform morphometry on transport mode, with impact‐type abrasion dominating areas of higher platform roughness. Results of the clast transport experiments indicate that abrasion occurs under non‐storm wave energy conditions with observable geomorphological effects. We suggest that abrasion by clasts is an important component of platform erosion on high energy Atlantic coastlines, particularly over longer timescales, and that the morphogenetic link between the cliff and the platform is important in this context as the sediment supplied by the cliff is used to abrade the platform. © 2018 John Wiley & Sons, Ltd.