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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
of peat slides. To avoid this, GSNI now routinely advises the Planning Service to ensure that the EnvironmentalImpact Assessments required to accompany applications for such developments consider peat slide risk andinclude information regarding peat depth and slope stability assessments.7.4 Land Use Planning and Development Control in LandslideSusceptible AreasThe system for land use planning in Northern Ireland differs from those currently operating elsewhere in theUnited Kingdom and the Republic of Ireland.In Northern Ireland, planning and development control is a centralised function and is primarily the responsibilityof the Planning Service, an agency of the Department of the Environment. The Planning Service develops andimplements Government planning policies and development plans in Northern Ireland.The Planning Service’s website (http://www.planningni.gov.uk/) summarises the role of the agency as follows:-“The planning system exists to regulate the development and the use of land in the public interest. TheDepartment’s functions, in relation to planning, are set out in the Planning (Northern Ireland) Order 1991. Therole of the Agency is to administer most of these functions. All planning decisions up until 14 October 2002were taken under the authority of the Minister of the Department of Environment. Following the suspension ofthe Northern Ireland Assembly the Parliamentary Under Secretary of State at the Northern Ireland Office hasexercised that authority.”The GSNI acts as one of the Planning Service’s statutory consultees and provides advice on a range ofgeologically related planning matters. Consultation takes place at various stages in the planning process,including planning policy development, regional and area planning, and development control.GSNI maps landslides and areas of ground instability in the course of its systematic geological resurveyprogramme in Northern Ireland, and landslides are represented on the published 1:50,000 scale geologicalmap series. GSNI is therefore uniquely placed to advise the Planning Service and identify potential landslidehazards which are potentially areas of planning constraint.The Planning (Environmental Impact Assessment) Regulations (Northern Ireland) 1999 require applications forcertain categories of development to undergo Environmental Impact Assessment and be accompanied by anEnvironmental Statement. GSNI provides the Planning Service and the developer with generic, (or sometimessite specific) advice on geological factors, including landslide risks that are likely to impact on or be impactedby a particular development.Many of the landslides in Northern Ireland occur in remote areas or are of such minor extent that they pose nosignificant risk to the safety of humans, livestock, or infrastructure. Where landslides or ground instability doconstitute a significant constraint to surface land use they need to be brought to the attention of developers andplanning authorities alike.The biggest threat to the stability of a landslide prone site arises through ignorance of the risks of unregulateddevelopment that may undermine the toe of a landslide, overload unstable ground, or radically alter existingground drainage patterns. Detailed knowledge of the risk associated with landslides coupled with carefulmanagement of drainage, use of retaining walls, slope-grading etc., can often minimise the effects of furthermovement on existing dwellings and infrastructure.“A Planning Strategy for Rural Northern Ireland” (Department of the Environment for Northern Ireland, 1993)outlines a policy for restricting development in unstable areas (PSU10). A more detailed Planning PolicyStatement along the lines of PPG 14 “Development on Unstable Ground”, currently in operation in England andWales, could be a useful resource to support planners and developers in Northern Ireland.7.5 Some Thoughts about the FutureIt is difficult to predict if and how the current levels and types of landslides and slope instability experienced inNorthern Ireland will be affected by predicted changes in global climate. Existing slopes, both natural andartificial, (eg. railway and road embankments/cuttings) may also be vulnerable to future climatic changes.Current predictions for climate change in Northern Ireland include: overall warming with rises in precipitationand potential evapotranspiration. Winter gales are predicted to decrease in frequency but increase in severity.77
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Landslides in IrelandGeological Sur
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LANDSLIDESinIRELANDEditorRonnie Cre
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CONTENTSPreface ...................
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Fig. 4.3 Forces caused by water in
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PREFACEUntil recently Ireland has b
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een very important in populating th
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involves a report on the current st
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Main Objectives• Increase public/
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1. INTRODUCTIONRonnie Creighton1.1
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1.3 The Landslides PublicationThis
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Peat flows are not nearly so well d
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In Ireland the Quaternary or uncons
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Journal - published papersLetter -
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Fig. 3.1 Two images showing the use
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Table 3.1 Landslide Events Per Coun
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Fig. 3.3 Location map of the Pollat
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3.7.4 Quaternary GeologyQuaternary
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3.8 The Derrybrien Landslide - 2003
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• The classification scheme shoul
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The force causing the block to slid
Page 42 and 43: Plate 4.1 Herringbone drainage syst
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Page 46 and 47: It is well known by research at Uni
Page 48 and 49: 5. LANDSLIDE SUSCEPTIBILITY MAPPING
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Page 52 and 53: 5.1.4 Mapping and GISBy definition,
Page 54 and 55: Platform / sensor pixel resolution(
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Page 62 and 63: elationships between developed susc
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Page 66 and 67: 50Fig. 5.12. Landslide susceptibili
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Page 72 and 73: with slope, overall 20-25% of all e
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Page 79 and 80: CHAPTER 5.2 - TABLE APPENDIXBedrock
Page 81 and 82: 6. LANDSLIDES AND PLANNINGAileen Do
Page 83 and 84: 6.2.4 Development ManagementThe phy
Page 85 and 86: 6.5 Current Practice on Landslides
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Page 90 and 91: 2. MudflowsPlate 7.1 Rotational Lan
Page 95 and 96: 8. RESEARCH ON IRISH LANDSLIDESKoen
Page 97 and 98: 8.4 Research. Post-2003 AbstractsTa
Page 99 and 100: Identifying, recognizing, and predi
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Page 103 and 104: Steep slopes in glacial tillMichael
Page 105 and 106: 9. RECOMMENDATIONS FOR FUTURE WORK9
Page 107 and 108: Priority 1 Peat slides and peat str
Page 109 and 110: TEXT REFERENCESAcreman, M., 1991. T
Page 111 and 112: Skipper, J., Follett, B., Menkiti,
Page 113 and 114: APPENDIX 2Glossary of TermsBlanket
Page 115 and 116: APPENDIX 3Nomenclature for Landslid
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Page 123 and 124: Hammond, R. 1979. The Peatlands of
Page 125: APPENDIX 7Useful Web Linkswww.gsi.i
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