Maps highlight landslide risk areas

The third wet summer in succession - rainfall for July alone was more than three times above normal in parts of Munster and Leinster - again sparks fears of landslides.

We've had several examples in recent years of unexpected slippages which are sometimes described as ‘Ireland's greatest natural hazards', given that we don't have even more devastating phenomena such as earthquakes and volcanoes.

Landslides are on the increase due mainly to climate change and man's activities, including wind farm construction. Most occur in elevated, bog-covered districts which are subject to very heavy rainfall. Well over 400 landslides have been recorded and damage caused has been well documented - houses, roads, bridges and even people have been swept away.

But, some action is being taken in a bid to prevent, or at least anticipate the danger of such happenings. The Geological Survey of Ireland (GSI) is drawing up maps which will highlight areas at risk. Importantly, such maps will become part of the planning process. The idea is to give warnings to people who might be thinking of carrying out developments in areas susceptible to landslides.

Work on the project started last year and is expected to take five years to complete. The initial focus is on the Dublin and Cork areas and it will eventually include the entire country, north and south.

Experts are predicting wetter winters, especially in the west, and drier summers, in the east. There will also be more intense downpours of rain and rising sea levels, leading to bigger waves crashing into soft coastlines, resulting in erosion and cliff collapses.

However, it's not just coastal and bogland areas that are vulnerable, as Dr Ronnie Creighton, GSI landslides project manager, pointed out in the July issue of Science Spin magazine.

"A lot of emphasis is on peat because that is where the slides are happening with heavy rain and so on. We (also) want to look at landslide hazard to commercial buildings and settlements," he said.

The vast amount of construction that took place during the economic boom has created more risks. Houses, other buildings and windfarms were erected in boggy areas, sometimes making land unstable and more prone to slippage when heavy rains came.

One of the most notable landslides to occur in recent times was at Pollatomish, Co Mayo, in 2003. It caused a lot of damage to property and wrecked several houses.

Pollatomish is, according to Dr Creighton, a good example of the type of terrain where landslides are likely to occur. Blanket bog lay on top of a steep slope, with bog also down the sides. When torrential rains came in September, water got into the cracks and saturated the peat.

Dr Creighton said the peat then became ‘buoyed up' and gravity brought it down the slope. He compared the terrifying movement of a huge mass of liquid peat to a hovercraft skimming over water.

Last September, peat became unstable in the Kielduff area, near Tralee, Co Kerry, damaging a bridge and a road and pouring tonnes of floating bog into a river. Local people blamed wind farm developments in the area for destabilising the bogland.

There are numerous examples of cliff collapses around the coast, often undermining public roads, with recent examples at Rossbeigh, Dunquin and Inch, all on the west Kerry coast.

The GSI mapping project is the first to be done on a large scale in Ireland and Britain. The maps are intended for general use and will be freely available. They are also intended to be easy to read, with three colours to mark high, medium and low risk areas.

People are urged to be extremely careful about areas with peat deposits where there has been a dry summer followed by periods of heavy rain. People are also advised to be aware of factors that can trigger a landslide, such as heavy rainfall over a short spell, or intense construction work that undercuts a peaty slope.

By the time the project is completed in 2013, Dr Creighton hopes to have useful maps, scientifically compiled, that will not alone identify high risk areas but will also heighten public awareness of landslides, what they are, why they happen and how dangerous they can be.

Some landslides have had heartrending human consequences, including one at Knocknageeha, near the Cork/Kerry border, in December 1896. During what was reported to be an extremely wet winter, the bog gave way and submerged a cottage that lay in its path. Quarry worker Con Donnelly, his wife, Johanna, and six of their children were asleep and all lost their lives. Local people reported hearing noise like thunder on that fateful night.

The tragedy is still spoken of in the area and a monument marks the spot where the Donnelly home was located.