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7. LANDSLIDES IN NORTHERN IRELANDTerence JohnstonLandslides occur in a number of different geological settings in Northern Ireland, and, in certain situations,constitute significant geohazards. The principal areas at risk are identified on the 1:50,000 and 1:250,000scale geological maps published by the Geological Survey of Northern Ireland (GSNI).7.1 Antrim Plateau Escarpment Instability (Counties Antrimand Londonderry)Landslips and associated ground instability are common features around the edge of the basalt plateau inCounties Antrim and Londonderry where they contribute in a large part to the landscape character (Fig. 7.1).Fig. 7.1 Principal Areas of Landslides Around the BasaltPlateau (Counties Antrim & Londonderry)72
Three principal categories of slope instability can be recognised:1. Rotational Landslips2. Mudflows and Debris Flows3. Rock Falls1. Rotational LandslipsAt a number of locations (Fig. 7.1) the edge of the Antrim Basalt Plateau consists of large scale, deep-seated,multiple rotational landslip features. The mechanisms behind this instability are directly related to the geologicalsuccession and the geomorphological processes that subsequently sculpted the landscape. The plateau edgeis capped by hard “competent” rocks: basalt lavas (Antrim Lava Group, Tertiary) and chalk (Ulster WhiteLimestone Formation, Cretaceous). These rocks overlie softer, less competent, impermeable mudstone:(Waterloo Mudstone Formation, Jurassic and the Penarth Group & Mercia Mudstone Groups, Triassic) (Fig.7.2 and Plate 7.1).Fig. 7.2 Generalised Landslip Model Co Antrim (Crown Copyright)During the last ice age, ice sheets flowed along the edge of the plateau eroding the soft mudstones rocks at itsbase. This undercut and oversteepened slope became inherently unstable. Along the plateau edge, failurestook place on the vertical and steeply inclined surfaces within the chalk and basalt and along more shallowlyinclined surfaces within the underlying more plastic mudstones (Fig. 7.2).The large, older rotational landslide blocks have, through time, reached a state of equilibrium. These areas dohowever remain susceptible to ground movement and remain at risk of rock falls, shallow slumps and translationalslides. In north and west Belfast an extensive area of palaeo-landslips continues to be a significant constrainton development. Where previous development has taken place on landslipped ground, dwellings and infrastructurefrequently suffer from cracking and disruption of foundations as a result of continuing ground movements.Stephens (1964) linked the large scale slip features at Benevenagh, County Londonderry and at Glenarm, CoAntrim to glacial action. Carney (1974) carried out a study of the landslide complexes along the Antrim coastusing aerial photographs and applied his interpretation of the geomorphological history of the area as follows:“In late Tertiary times the lava plateau was affected by a series of erosion cycles seen as bench levels at 600m,310m and 250m. Formation of the landslip escarpment may have occurred towards the end of this period afterthe junction between the Ulster White Limestone Formation and Waterloo Mudstone Formation had beenexposed to marine erosion”.During the early stages of glaciation in Northern Ireland, ice spread across Antrim from centres in Scotland andIreland. The “Irish” ice spread eastwards across the Antrim Plateau and “Scottish” ice moved southwardsacross parts of Co. Antrim and Co. Down. A combination of the eastwards moving Irish ice and topographyrestricted the spread of the Scottish ice to the northern and eastern coastal fringes of Antrim (Bazley, 2004).Glacial erosion removed much of the pre-glacial landslip debris along the edge of the Antrim escarpment. Bythe time the ice had melted and retreated, the edge of the escarpment had been oversteepened and unconstrainedthus precipitating a new phase of landslipping.73
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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
Page 36 and 37: 3.8 The Derrybrien Landslide - 2003
Page 38 and 39: • The classification scheme shoul
Page 40 and 41: The force causing the block to slid
Page 42 and 43: Plate 4.1 Herringbone drainage syst
Page 44 and 45: 1210Number of events864Raised bogBl
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Page 48 and 49: 5. LANDSLIDE SUSCEPTIBILITY MAPPING
Page 50 and 51: Two simplified hypothetical example
Page 52 and 53: 5.1.4 Mapping and GISBy definition,
Page 54 and 55: Platform / sensor pixel resolution(
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Page 58 and 59: 42Fig. 5.5 Peat and peaty podzols f
Page 60 and 61: for susceptibility mapping purposes
Page 62 and 63: elationships between developed susc
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Page 66 and 67: 50Fig. 5.12. Landslide susceptibili
Page 68 and 69: 52Table 5.6. Landslide classificati
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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
Page 90 and 91: 2. MudflowsPlate 7.1 Rotational Lan
Page 92 and 93: 7.2 Carboniferous Cliff Lines (Co F
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
Page 117 and 118: APPENDIX 4101
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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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