Coastal boulder deposits in Galway Bay and the Aran Islands, western Ireland

Along European shorelines exposed to the open Atlantic, the central west coast of Ireland shows extraordinary imprints of wave events, along kilometres of coastline, among them dislocated boulders up to 50 m above sea level and weighing more than 100 t. This paper documents the geomorphology and sedimentology of these littoral deposits and the processes involved in their dislocation, based on field studies and a number of absolute age dates. It also discusses formerly published hypotheses on the genesis and ages of these rare features and the possibility of their tsunamigenic origin. Arguments to question the modern storm deposition interpretation include archaeological remains dating back 2,000 years at the cliff top, preservation of older landward ridges never reworked by subsequent wave events, numerical ages of cliff top ridges and boulder deposits yielding ages of 3,000 years BP, and in particular the existence of similar coarse deposits along the leeward side of the Aran islands as well as in the protected Galway Bay, where no large storm waves occur.