Burger Landmarks

The Burren is a limestone area in the North of County Clare and East of County Galway on West Ireland. The area is approximately 500 square kilometres in size. The word “Burren” comes from an Irish word “Boíreann” meaning a rocky place.
The karst proces created a geomorphological feature limestone pavement which which can be seen along the Atlantic Way road. The Burren area is designated as UNESCO Global Geopark. The Burren National Park is in the South-eastern corner of the Burren and is approximately 15 square kilometres in size. The Burren National Park covers a small part of the Burren and is the smallest of the six National Parks in Ireland, while the adjacent territory, including the Cliffs of Moher, is included in the Burren and Cliffs of Moher Geopark.

The area is formed from a thick succession of sedimentary rocks, largely limestones but also including sandstones, mudstones and siltstones. All of the solid rocks exposed at the surface are of Carboniferous age though they are underlain at depth by Old Red Sandstone of Devonian age which in turn overlies rocks of Lower Palaeozoic age. None of the pre-Carboniferous rocks is seen at the surface in the area. The limestones, which date from the Visean stage of the early Carboniferous, formed as sediments in a tropical sea approximately 325 million years ago. The strata contain fossil corals, crinoids, sea urchins and ammonites. This bed of limestone is up to 800 metres thick. In the north and west it lies on a shelf of Galway granite which supported the upper layers, preventing shifts like those that created the "twisted" hills Knockanes and Mullaghmore. The limestone also extends below Galway Bay out to the Aran Islands and to the east into the Gort plain.

Later in the Carboniferous (about ~318 million years ago), the limestone was covered by darker sand and mud that later turned into shale (the lower "Clare Shales") and sandstone (the upper "Millstone Grit"). These layers reached a thickness of up to 330 metres in north Clare. These top layers protected the underlying limestone from erosion for millions of years before being largely stripped away by glaciers, except in the south west, where they still extend from Doolin to Slieve Elva, Lisdoonvarna, Kilfenora and to the western shore of Lake Inchiquin. One "island" of shale is the hill Poulacapple, southwest of Ballyvaughan, where an upland moor has formed on top of the impermeable shale layers.

Glaciation during the late Quaternary period, beginning about one million years ago, facilitated greater denudation. Glaciers expanded and retreated over the region several times. Of the last two periods the first was the more pronounced, covering the whole of the Burren. The last advance of the ice cover was more limited, affecting only the eastern Burren.

The result is that The Burren is one of the finest examples of glacio-karst landscape in the world. The effects of the last glacial period (the Midlandian) are most in evidence, with The Burren overrun by ice during this glaciation. The impact of earlier karstification (solutional erosion) has been eliminated by the last glacial period. So any surface karstification now seen dates from approximately 10,000 years ago and The Burren karst is thus very recent in geological terms.

Solutional processes have widened and deepened the grikes of the limestone pavement. Pre-existing lines of weakness in the rock (vertical joints) contribute to the formation of extensive fissures separated by clints (flat pavement like slabs). The rock karstification facilitates the formation of subterranean drainage. This has formed numerous cave systems of which more than 50 kilometres have been mapped.

Due to the processes mentioned, there are very few permanent surface rivers in the region. The Caher, flowing into the sea at Fanore, is one of the most stable. Some of the large valleys, mostly running south to north, that are still visible today are in fact the remains of pre-glacial river valleys. The rivers disappeared from the surface when the upper layers of stone had been stripped away.

Another characteristic features of The Burren are closed roughly circular depressions - poljes, with no surface outlets for water. Around 100 of these exist, mostly present in the eastern Burren. The most notable are the valleys of Kilcorney, Poulawilan, Caherconnel and Carran, generally stretching from northeast to southwest. The largest is the Carran polje, more than 3 kilometres long, up to a l1.5 kilometer wide and over 60 meters deep. This is where the pre-glacial rivers of the area first eroded away the upper layers and started to dissolve the exposed limestone. Some of the smaller ones were created when caves underneath collapsed.

Glaciers also deposited numerous granite and limestone erratics on the pavements. The former were carried south across Galway Bay by the second-to-last glaciation. Granite boulders can be found mostly in the north of the Burren. The final ice cover came from the northeast and mostly deposited limestone erratics. On Slieve Elva these are visible today at elevations of up to 300 metres above sea level. The characteristic terracing of the hills occurred when vertical joints weathered and large blocks of limestone fell off and were further eroded away.

Towards the very end of the Ice Age the glaciers ended for a time at Fanore. At that time, Slieve Elva and Knockauns hill alone rose above the surrounding ice fields. The valleys facing Galway Bay had been widened considerably by glacial action, first when the ice moved south from Connemara and then when meltwater sought a runoff. When the ice finally retreated it also left moraines in valley bottoms and the characteristic drumlins (most of them on top of the shale and sandstone to the south). The Caher Valley was almost choked up by deposited sand and rocks and these also piled up against the western slopes of Slieve Elva. It was this protective layer of sediment that has made surface streams locally possible once more. Today, the uplands' highest point is on the hill Slieve Elva, whose shale cover rises up to 345 metres above sea level.

Literature and sources:

Burren National Park - Geology, URL: https://www.burrennationalpark.ie/geology/ (quoted, 18. November 2022) ;
Clements, Paul: Burren Country: Travels Through an Irish Limestone Landscape, Cork: Collins Press, 2011 ;
Hennessy, R., McNamara, M., & Hoctor, Z., 2010 Stone, Water & Ice: A Geology Trip Through the Burren. Burren Connect Project, pp. 64. ;
Feehan, J., Korff, A. & O'Connell, J.W., The Book of the Burren, Irish Books and Media, 1991 .