Some morphological, morphometrical and sedimentological characteristics have been determined for relict periglacial boulder sheets and lobes on the upper slopes (>700 m OD) of Slieve Donard, Mountains of Mourne. The features occur principally on slopes of northerly and easterly aspect, include 'stone-banked', 'turf-banked' and 'unvegetated' varieties, and are developed on gradients of 10-27°. In terms of their dimensions, riser and tread gradients, and boulder characteristics (dimensions, sorting, form and fabric) the sheets and lobes are not of uniform size and form and in those respects compare favourably with examples described from Great Britain and elsewhere in the world. The process(es) of downslope movement is/are not easy to explain unless a finegrained, frost-susceptible material capable of undergoing gelifluction underlies the boulders. The likelihood of such material being present and its possible origin are discussed.
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.
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