Examples of recent rockfalls from basalt cliffs in Northern Ireland

Abstract

Two examples of recent rockfalls from basalt cliffs in Northern Ireland are described and some trigger mechanisms suggested. The Downhill rockfall of June 2002 resulted in derailment of the Londonderry-Belfast train and occurred following two months of above average rainfall. The Trostan rockfall(s) has (have) resulted in basalt boulders accumulating on the track bed of a late nineteenth century mineral railway, the track having been removed by 1900. Rockfall timing(s) and cause(s) are not known with certainty but the possibility of distant seismic activity acting as a trigger mechanism is introduced. Both examples exceed in magnitude rockfall events recorded elsewhere on the Ulster basalts, and demonstrate the unstable nature of basalt cliffs and the hazards posed to transport routes engineered along their base.