Summary of site:
The beach at Ballycastle consists predominantly of coarse sandy gravel and is generally much coarser than the beaches further west along this coast. The reason for this is the origin of the sand, which is derived from a series of substantial deltaic accumulations in the Carey River valley inland to the south east. These date from the melting of the regional ice sheet at the end of the last glaciation, when melt waters stripped the glacial debris from the area forming marine deltas (at a series of declining sea levels) or possibly lake deltas in ice-dammed melt water. Exceptionally high modern rainfall dislodges large volumes of these sands and gravels which wash down the river, entering the sea at the west end of Ballycastle Bay. Here they settle to the sea bed and are distributed by waves with differing characteristics from the Irish Sea and the North Atlantic. Near the river mouth at the west end of the bay the sediments form into crescent shaped bars, up to 300m long, and are circulated by waves and currents in a series of interacting cells along the shore. The general movement of the sand along the beach is east to west, which means that the east end must be replenished in the process.
Behind the beach, and built on to it, is a series of dunes (banks of wind-blown sand). The most recent dunes form a belt 600m long and 150m deep. They are backed towards the Carey River by an older series. Although the dunes are stable at present, two buried roads confirm that there has been significant wind drifting since the eighteenth century.
Interpretation of the beach and dune complex is difficult due to extensive and disruptive human intervention. Activities as diverse as coal mining, glass making, harbour and golf course construction have all modified the dynamics of the beach - but how, and with what degree of impact, awaits future research.