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The percentage of events occurring on each of these six conditioning factors was computed. This percentagewas subsequently applied to measure the weight of each conditioning factor for the susceptibility map production(e.g. 27% of Bedrock Slides occur on Shale. A weight of 27 was given to areas underlain by Shale bedrock).The same principle was applied to each landslide type combined with each conditioning factor.BedrockThe bedrock geology of the Bréifne area is rather complex. Numerous bedrock formations are present in thearea and bedrock type is a very important factor in susceptibility to landsliding. The percentage of eventsoccurring on each formation was calculated. A simplified bedrock geology map, containing nine bedrock typeswas selected for the analysis. The reasons for using a simplified map of nine bedrock types are listed below:• The bedrock formations are regionally distributed and would give higher weights in areas where eventsare concentrated.• A smaller number of bedrock types in the analysis will give a better distribution of weights.• Simplified bedrock geology types have similar structural, petrological and lithological characteristics.The percentages calculated for each landslide type are shown in Fig. 5.13. It should be noted that Limestone,Sandstone and Shale comprise the highest percentages of events.Fig. 5.13 Percentage of Landslides by Bedrock type.Soil parent material (Subsoil)Not all of the study area is covered by this thematic dataset. The Co. Leitrim dataset was not available for thisstudy. A total of 399 events are within the areas covered by Co. Sligo and Co. Cavan. These were categorizedas follows.• 66 Bedrock slides• 128 Peat slides• 55 Flow• 144 FallsOnly five soil parent material types were involved in the slide events in the area. Final calculations (Fig. 5.14)show bedrock slides and falls occurring mostly on areas where rock is at or close to the surface. Peat slidestake place in peat-covered areas, but, according to the IFS parent material map, some occurrences arehappening in non-peat covered areas. This may be explained by the fact that only those areas with peat of 1m+in depth are mapped as peat covered, and slides may occur in areas of thin peat. Flows chiefly occur on rockat or near surface. This is attributable to the fact that 60% of the flows occur in areas dominated by shale, orlimestone and shale, and these are bedrock types susceptible to flowing when water saturated.54
Soil Parent Material%10 09080706050403020100% Events% Bedrock slides% Peatslides% Flo ws% FallsRock At orNear Surf aceTill Cutover Peat Peat CollluviumSoil Parent Material typeLandcover MapFig. 5.14 Percentage of Landslides by Soil parent material type.The landcover map covers the whole area within the Republic of Ireland. The map has 15 different landcovertypes. Landslide events occur in 10 of these classes. All events mapped have been used to compute statistics.Final results are shown in Fig. 5.15.Most of the land and peat slides occur on Bog and Heath. Peat cover was one of the factors used to decidewhere to focus the survey and this may have influenced the distribution of the data. It also has to be noted thatvery few events are occurring on bare rock or rocky complex. This is due to the small area (0.2% of the total)covered by these two landcover types. A similar situation is shown in bog, this landcover type covers only 0.8%of the map.%90807060504030Landcover% Events% Bedrock slides% Peatslides% Flows% Falls20100Bare RockBog&HeathBogCut&Eroding BogDry GrasslandForest(U) & ScrubMature ForestRocky ComplexUnclassifiedWet GrasslandLandcover typeFig. 5.15 Percentage of Landslides by land cover type.SlopeThe slope map was generated from the DEM for Bréifne, using Spatial Analyst Extension in ArcGIS 8.3 software.Slope is considered a major conditioning factor for landslide occurrence, although while landslide type variedSlope7060%50403020100Less than 10 10 to 20 20 to 30 30 to 40 M ore than 40% Events% Bedrock slides% Peatslides% Flo ws% FallsSlope gradient in degreesFig. 5.16 Percentage of Landslides by slope gradient55
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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
Page 19: 1.3 The Landslides PublicationThis
Page 22 and 23: Peat flows are not nearly so well d
Page 24 and 25: In Ireland the Quaternary or uncons
Page 26 and 27: Journal - published papersLetter -
Page 28 and 29: Fig. 3.1 Two images showing the use
Page 30 and 31: Table 3.1 Landslide Events Per Coun
Page 32 and 33: Fig. 3.3 Location map of the Pollat
Page 34 and 35: 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
Page 46 and 47: It is well known by research at Uni
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(
Page 56 and 57: For this initial run, the criteria
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
Page 64 and 65: The methodology used to derive the
Page 66 and 67: 50Fig. 5.12. Landslide susceptibili
Page 68 and 69: 52Table 5.6. Landslide classificati
Page 72 and 73: with slope, overall 20-25% of all e
Page 74 and 75: As the dataset was not available at
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 88 and 89: 7. LANDSLIDES IN NORTHERN IRELANDTe
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
Page 101 and 102: In the case of vulnerability mappin
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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105
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Hammond, R. 1979. The Peatlands of
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APPENDIX 7Useful Web Linkswww.gsi.i
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