Aeolian processes and deposits in northwest Ireland

Abstract

Abstract The exposed Atlantic coast of northwest Ireland supports numerous dunefields derived largely from glacigenic deposits in the area of the present continental shelf. The present-day dunes began to form about 5000 to 6000 years bp at, or just after, the mid-Holocene sea-level peak which reached a maximum of + 3 m OD on parts of the County Antrim coast. As the sea-level fell so sediment was transferred onshore accumulating as beach ridges and dunes. Some dunes are perched on gravel ridges of marine origin that were exposed long enough to aeolian processes to allow the formation of ventifacts. Since about 4000 years bp the primary sediment budget has become strongly negative, allowing morphological reworking of many dune systems. The processes of erosion may well have been triggered by climatic changes or human impacts or a mixture of both. Periods of dune instability are marked by the widespread engulfment of former soil surfaces by large-scale mobile bedforms, the transport of sand inland and the formation of extensive sand sheets. At Maghera, County Donegal and Downhill, County Londonderry there are ramp dunes against former sea cliffs, and between Portstewart, County Londonderry and Portrush, County Antrim extensive cliff top dunes formed in the late Holocene which are now isolated from their original sediment source. Non-coastal aeolian sands are of limited extent in northwest Ireland, but some local examples are described.