The Geological Survey of Ireland says an extreme weather event caused last month's landslides in north Mayo, and has warned that further slides could occur in upland areas with similar geological and weather conditions.
A preliminary report for Mayo County Council by the GSI has ruled out underlying geology on Dooncarton mountain as the cause of over 20 landslides between Pollathomas and Glengad on the evening of September 19th.
The geologists who wrote the report also rule out the construction of the radar station on Dooncarton Hill, and do not find any link with overgrazing, or with Enterprise Energy Ireland's gas terminal preparations in the Glengad area.
Had the west coast experienced the sort of rainfall that was recorded on the east coast this week, there could have been "serious problems" at both Pollathomas and at Derrybrien, south Galway, where a similar landslide occurred a week ago, according to the GSI.
Other upland areas with similar configurations of peat and impermeable rock could also have been affected, and are still at risk, said Mr Koen Verbruggen, senior geologist at the GSI.
A Geographical Information Systems (GIS) survey of digital data shows that Dooncarton's bedrock is schist and sandstone, of low permeability and thus not absorbing rainfall to the extent limestone areas can.
While geological faults occur in the area, it is tectonically stable, the GSI report says, and the faults have no history of recent movement.
The report states that the exceptionally heavy rainfall in the area on September 19th caused the peat bog to slide on the steep mountain slopes, and the situation was further exacerbated by the relatively dry state of the peat after a long dry summer.
Cracks had appeared in the thin peat bog cover, and the rain saturated the peat and then found easy passage to the base.
Mr Verbruggen says that overgrazing was not a factor, nor would it have been in south Galway where most of the Derrybrien area is under afforestation.
"There was plenty of grass on the hills when we inspected it, although this is not to say that it may not have been overgrazed previous to this," he says.
The GSI argument for Pollathomas underpins the thesis put forward by Prof Mike Williams, geologist at NUI, Galway, following last week's landslide at Derrybrien.
As Prof Williams told The Irish Times last week, the long dry summer would have caused the peat to perish and its roots to shrink and shrivel, leaving no firm hold on the underlying bedrock.
Prof Williams has charted previous landslides - four in the Co Galway area from 1740 to 1890 alone. He discounts overgrazing as being a possible cause.
"Overgrazing is a major problem in the west of Ireland, but this is only over the last 20 years, and REPS schemes [Rural Environment Protection\] have been introduced to tackle this by Teagasc.
"The experience of areas in Africa and South America shows us that the more animals are on the hills, the more unstable the soil can become. However, we have no evidence of this having such a dramatic effect here."
In the Derrybrien case, there was no rainfall, but over 60 contractors attached to Ascon and to Coillte were preparing the area for a 60 megawatt wind farm - planned by the ESB subsidiary, Hibernian Wind Energy - when one kilometre of mountainside, some 100 metres wide, rolled over and spilled into a gorge attached to the Lough Cutra river system.
Significantly, a Bord Pleanála inspector's report into one phase of the Derrybrien project - covered by three sets of planning permission - said that the local authority noted information on the reinstatement of the site, visual impact and soil erosion were "poorly addressed" in the environmental impact statement (EIS) prepared by the owners.
This begs the question about the use of the geologists to assess planning applications.
Guidelines prepared last year by the Institute of Geologists of Ireland had recommended that the geology chapter of an EIS should be signed off by a professional geologist. It has called for professional geologists to be employed by county councils, and says that there should be an increase in staffing and funding for the GSI.
With or without the resources, the GSI intends to prepare an indicative study which identifies areas at most risk of such landslides occurring - such as the combination of peat and impermeable bedrock on Dooncarton mountain. The variable will be the sort of freak weather conditions experienced in Ireland this year.
An Irish Farmers' Association analysis of farm losses in the area showed that a total of €620,000 had been lost and farmers in the area could reclaim land damaged and replace livestock, farm machinery and farm buildings.
It showed 62 farmers were affected and repair to land damaged by the the landslide accounted for approximately €280,000, with fencing accounting for €132,000, livestock losses (approximately 550 sheep) accounting for €32,000, machinery and farm buildings accounting for €165,00, and fodder losses amounting to €10,000.
