Our rock'n'roll past is a key to Ireland's geological heritage

ANOTHER LIFE:AT THE WINDWARD coast of the Aran Islands, the lip of the high limestone cliffs is buckled and torn, its rock slabs lifting from their horizontal bedding like the pages of a much-thumbed book. Over time, thousands of the slabs have been thrown back several metres from the edge, as if to clear a wide promenade for human walkers. Whole or broken, they are piled into a vast ridge of "storm beach", five kilometres long in places and several metres high. Some of the bigger slabs weigh tens of tonnes, beyond any human shifting.

Comparatively few of the millions of visitors to Aran get as far as these wilder reaches of the islands; the mass of little high-walled fields, with its maze of narrow paths and secret stiles, does not encourage it. And so, while the ritual tour of the fort of Dun Aengus is awesome enough reward, tourists usually miss out on a phenomenon that surpasses even the Giant’s Causeway in potential for human awe.

The Aran storm beaches mount to 50m above the sea – the highest anywhere in the world. And the piling of their huge slabs, or “megaclasts” as geologists call them, has demanded a credible cause.

On due reflection, most people would accept that, however huge the storms assailing the islands, they are hardly capable of tossing rocks up over the cliff from the bottom of the sea. Tim Robinson admits to giving the idea room in some of his early writing, but by the time he came to his magisterial Stones of Aran (1986), he could set out the true, and hardly less gobsmacking, explanation.

Ireland’s earth scientists are now fairly content with the basic mechanics. Massive waves in exceptional storms, slamming against the cliffs, have lifted loosened slabs from their sockets at the edge and tumbled and swept them back on to the storm beach. As Robinson summed it up: “These mighty works have been done partly by gale-by-gale, winter-by-winter processes. . . and partly no doubt by more drastic events like the ‘Night of the Big Wind’ in 1839.”

Outside Ireland, however, an alternative theory has been on offer, recently among Australian scientists stirred to international study by the impact of the great Indian Ocean tsunami of Christmas 2004. A team led by Prof Anja Scheffers of Southern Cross University in New South Wales looked around the world for high-level boulder deposits that could have been caused by tsunamis.

The storm-beach megaclasts of Aran and Shetland came under close scrutiny. The team’s conclusion, published in 2009, was that “no evidence . . . exists for storm wave dislocation of . . . boulders found at altitudes of [up to] 20m a.s.l..”

Indeed, “no calculations of possible storm wave heights, storm wave physics, or ages of the deposits and no descriptions of extaordinary storms are sufficient to explain these displacements”, and “alternative explanations, such as tsunamis, should be considered”.

This brought a swift rebuttal from Scottish and Irish earth scientists. Among them, Dr D Michael Williams, professor of earth and ocean sciences at NUI Galway, has given particular study to the exact mechanics of the wave action.

In a 2010 paper for the Irish Journal of Earth Sciences, replete with diagrams, equations and photographs, he showed how waves overtopping the Aran cliffs produce a collapsing water mass and a high-velocity landward bore well able to carry slabs weighing tens of tonnes inwards to the slope of the storm beach.

His account did not, however, satisfy everybody. The Australians had radiocarbon-dated organic material from beneath the Aran megaclasts. In citing this last year, a British geographer, Dr Jasper Knight of Loughborough University, said it showed that the slabs were placed “episodically throughout the last 3,000 years, and, although there may be correspondence with periods of high storminess, a tsunamigenic origin cannot be rejected.”

Whatever the mechanism – and my money’s still on Dr Williams – such a spectacular phenomenon surely deserves a top place in the current promotion of Ireland’s geological heritage.

“Geodiversity” is the new word for the importance of rocks and earth processes in shaping the natural world. “Geoparks” and “geotourists” come swiftly in its wake. Ireland has a remarkable mix of scenery, with many special sites to speak for contortions of ancient bedrock, opening and closing of oceans, and grand sculpture of the glaciers, along with early human ventures in mining and quarrying. County after county has been waking to its new resource.

The enthusiasm among Ireland’s geologists for sharing with all landscape-lovers has inspired The Secrets of Stone, a seminar today in the National Museum of Ireland’s Palatine Room, at Collins Barracks in Dublin. Mary Mulvihill, Rosaleen Dwyer, Nigel Monaghan and Matthew Parkes are among the speakers.

Massive waves in exceptional storms have lifted loosened slabs from their sockets and tumbled and swept them back on to the storm beach

Eye on nature

My son Shane and I saw our first great spotted woodpecker in the woods near the Ordnance Survey Centre in the Phoenix Park. He had a red patch on his head and rump, black and white dots along the wing and a strong pecking beak.

Michael Quinn, Maynooth, Co Kildare

When chiselling a hole the woodpecker does not tap as quickly as when the male performs his drumming.

I spent a very enjoyable afternoon watching a red squirrel playing in the oak tree in my garden.

Muriel Williams, Enniskerry, Co Wicklow

On a regular jaunt on my paddle board around Killiney Bay, I saw a family of otters swimming before they got out and disappeared among the rocks. They were about a foot long and chocolate- brown, and their tails appeared to have a triangular cross section. I also saw what appeared to be a duck standing on a rock. It was a bright-red ginger colour and had a black beak with white around it and black-tipped wings.

Jules Charlton, Dún Laoghaire, Co Dublin.

Otters are two or three feet in body length, but they might have been mink, which are much smaller. The bird could have been a ruddy duck except its beak is grey or blue.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address