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7.2 Carboniferous Cliff Lines (Co Fermanagh)Landslides occur along the cliff lines at Magho [H075 580], Belmore Mountain [H154 415], and CuilcaghMountain [H110 293]. In most cases these cliffs are capped by hard limestone strata (Dartry LimestoneFormation, Carboniferous) and interbedded limestones/mudstones (Glencar Limestone Formation), which overlieless competent mudstone-dominant formations (Benbulben Mudstone Formation and Bundoran Shale Formation).Glacial erosion caused oversteepening of the Fermanagh cliff resulting in rotational landsliding and theaccumulation of block screes. The major rotational landslips are now mainly dormant although smaller scalesecondary slips still occur. At Magho, for example, large rotational slips and secondary slumps continue tocause instability problems and affect the Enniskillen to Belleek road (A46) close to the southern shore of LowerLough Erne. At Cuilcagh Mountain, on the Co. Fermanagh/Co. Leitrim border, where massive blocky sandstone(Lackagh Sandstone Formation & Briscloonagh Sandstone Formation) overlies a mudstone-dominated succession(Dergvone Shale Formation), erosion and oversteepening of the cliff-face has resulted in landslips and topplingleading to an accumulation of a large block scree.7.3 Peat Failure (Bog Bursts and Peat Slides)Peat slides and bog bursts are characteristically rapid mass movements that occur in areas of upland peat andare triggered by heavy and/or prolonged rain.Bog bursts usually involve rupture or tearing of the peat layer with liquefied peat often being expelled along themargin of the peat mass or through tears on the peat surface (Warburton et al., 2004).Peat slides by contrast occur as slab-like shallow translational failures that involve shearing at or just abovethe interface between the peat and an underlying low permeability mineral substrate.In Northern Ireland, bog failures have been documented in several areas:Co. Antrim: Slieve-an-Orra Hills (Tomlinson et al., 1982).Glendun (Colhoun et al., 1965).Sherry Hill (Wilson et al., 1993).Co. Fermanagh: Cuilcagh Area (Dykes and Kirk, 2001).Carrowmaculla (Tomlinson, 1981).On Cuilcagh Mountain, where relatively thin peat rests on modest slope angles, bog bursts appear to havebeen triggered by a combination of man-made alterations to the drainage regime induced by peat cutting andheavy rainfall.Peat Failure MechanismsThe mechanisms that lead to mass movement of peat are not yet fully understood, however a series of commonfactors have been identified (Tomlinson et al., 1982):1. The peat overlies a low permeability or impervious clay-rich mineral substrate.2. There is a convex slope or a slope with a break of slope at its head.3. Proximity to local drainage (seeps, groundwater flow, pipes, streams)4. Connectivity between surface drainage and the peat/impervious layer interface.Much of the upland peat cover in Northern Ireland has been drained and removed either completely or partiallyfor use as fuel, horticultural growing medium, or as part of general land improvements and reclamation. Theremaining intact areas of peat are increasingly valued as habitats worthy of conservation and, in some cases,have been designated by the Environment & Heritage Service of Northern Ireland as Areas of Special ScientificInterest (ASSI) eg. Cuilcagh Mountain, Co Fermanagh (ASSI 069).Reported bog burst and peat slide events in Northern Ireland have, to date, generally been of modest proportionsand have occurred in relatively remote locations away from human habitation. The recent catastrophic bogslide events at Derrybrien (Co. Galway) and Pollatomish (Co. Mayo) have however heightened awareness ofthe potential for bog failure in Northern Ireland.Coincidentally Northern Ireland has also recently experienced a growth in development of upland wind farms(with several more in the pipeline). In most cases these developments have been located in areas where full orpartial peat cover, moderate to steep slopes, and high average annual rainfall can potentially increase the risk76