Relict periglacial boulder sheets and lobes on Slieve Donard, mountains of Mourne, Northern Ireland

Abstract

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.

Key index words:

• Boulder sheets and lobes
• periglacial
• gelifluction
• Mourne Mountains