Storm-driven coastal boulder transport over two winter storm seasons on Inishmaan, Ireland

This work presents the results of a two-year coastal boulder study in Inishmaan, Ireland, where individual boulder motion was tracked using accelerometers, aerial photography, and on-ground surveys. The study monitored boulder movement across four sites during Winter 2022/23 ( n = 22), expanded in Winter 2023/24 ( n = 36), and prepositioned some boulders to be isolated on the supratidal shore or cliff platform to increase their exposure. Although coastal boulder deposits in Western Ireland have been studied extensively over recent decades and have been hypothesized to be active only in extreme winter storms, we observed multiple storm inundation events transporting boulders each year. Transport was likely for boulders on open platforms than those constrained by other boulders or topographic barriers, and smaller, lower-elevation boulders were more likely to be transported than larger, higher-elevation boulders. Transport directions were complex and net seaward boulder motion was not observed. Our results show that boulders were predominantly transported during storm events coinciding with high tide, highlighting the significant role of the tidal stage in mesotidal locations. These findings demonstrate that some coastal boulder deposits can be active annually, with isolated boulders particularly vulnerable to storm transport. With boulders moving more regularly than previously thought, there are implications for coastal planning, safety, and management. • Storm-driven transport (sliding, rolling, and jumping) logged with 10-min precision • Apple AirTags and UAVs were used to track boulders post-storm transport • Storms coinciding with high tide were necessary for boulder transport • Topography strongly influenced boulder transport initiation and distance