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5. LANDSLIDE SUSCEPTIBILITY MAPPING INIRELAND5.1 Landslide Susceptibility MappingRéamonn Fealy5.1.1 IntroductionOne of the first reactions that people may have to the notion of undertaking landslide risk assessment orhazard mapping Ireland might well be “Why?”. In Ireland we are not used to dealing with natural hazards orconsidering ourselves to be at risk from such hazards. In the main we are fortunate relative to other regions ofthe world in this regard. We see events like the South East Asian Tsunami of December 2004 or the devastationwrought by Hurricane Katrina in New Orleans and Hurricane Stan in South America in 2005 as being farremoved from us. Reports of the loss of life resulting from landslide activity in South America due to HurricaneStan reach us and our reactions, while sympathetic, are generally grounded in a sense of it could never happento us.It has been estimated in the literature that landslides are thought to result in the deaths of 600 people annuallyaround the globe (Aleotti and Chowdhury, 1999). Most people in Ireland will feel lucky that this hazard isgeographically removed from us. Most however will not be aware that 21 people died in such an event in 1708near Cappamore in Co. Limerick or that 8 people died in an event at Knocknageesha in Co. Kerry. The event atPollatomish in September 2003 was remarkable in that no injuries or loss of life resulted. The dramaticdescriptions of the experiences of those people who were fortunate enough to escape the torrent of water, peat,rock and soil that flowed down the mountain that night should be sufficient to cause most people to stop andthink more carefully about the potential danger posed by landslides in Ireland.While generally not considered to be frequently occurring events it should be borne in mind that our knowledgeof landslides in Ireland is limited. The database established by the Irish Landslides Working Group (ILWG) is inthe main formed only from the recent historical record. The earliest record in the database extends back onlyas far as 1488. Given such a short record, relative to geological timescales, the extent and frequency ofoccurrence that can be inferred is limited.The perception that landslides are too rare to cause concern is misguided and the apparent infrequency shouldnot be relied on as an excuse not to take the potential dangers posed by landslides very seriously. Societywould generally agree that one life lost would be too high a price to pay. As the death of a woman in a Welshseaside car park in Nefyn in 2001 shows, we as a society would be very unwise to underestimate the dangersposed by landslide events. Like many natural hazards, although the frequency may be low, the potential to doextreme damage and to result in human injury or death must always be considered.5.1.2 Hazard and risk assessmentOne of the most important actions in seeking to mitigate the potential damage caused by natural events is toidentify as precisely as possible the areas that are most likely to be affected by such events. Given thecomplexity of the factors involved in landslides this task is best dealt with in a multidisciplinary framework. Theemerging work in this area, which is well developed in those regions of the world most prone to landslidehazard, has generally proceeded within the framework of risk assessment.Risk assessment, although once the primary area of interest for the financial sector and high risk industries,has greatly expanded into the area of natural sciences. The methods and terminology employed in riskassessment provide a convenient structure to study and assess the potential of natural events to impact onsociety. However there are limitations to the application of the methodology not least of which is the fact thatit is a human constructed framework for assessment and response. Nature has proved countless times in thepast and will continue to do so in the future that we must not become over-reliant on human systems ofunderstanding. Events in nature are often extremely complex and it is vitally important that we seek to understandthe limitations in our approaches. By doing so we will ultimately benefit from improved responses to thehazards posed, resulting in improved protection from loss of property and life.32