The Burren

Many people wonder what’s so special about The Burren, and there’s no single answer to this question.  It really depends on what you’re interested in.  Here are some brief answers to many of the questions that visitors frequently ask us about this fascinating place.

Burren FAQ

What is it?

The Burren is an area of karst covering approx. 36,000 hectares (140 sq. miles) in north Co. Clare and a small part of south Co. Galway in Ireland.  Karst is defined as "rough limestone country with underground drainage" (Chambers), and practically everything you need to know about The Burren can be described in terms of these two elements - stone and water. From its original formation, to how it appears and is used today, the interaction of stone and water has been the defining feature of The Burren.

How was it formed?

Around 650 million years ago, that part of the Earth's crust now occupied by Ireland was located near the Equator at the bottom of a shallow sea.  The marine life (much of it microscopic) included organisms with hard shells composed of calcite. When they died, the shells settled on the floor of the sea.  Over millions of years, these shells compressed and cemented to form the limestone rock that we see today all over The Burren.  This is a simplified description - in fact there are many layers of different types of limestone reaching in places to a depth of almost 800 meters.  Some of the layers are separated by thin sheets of clay known as palaeosol. The limestone was finally covered (about 318 million years ago) by the second type of rock associated with this area, known as Clare shale.  Shale is formed in slow-moving water when very fine mud that has been washed down by rivers settles.  The Clare shales are about 2,500 meters deep in places and once covered all the limestone in The Burren.  The final phase in the formation of The Burren happened during the various Ice Ages when the glaciers advanced generally southward and stripped away the covering of shale to expose the underlying limestone.  The end of the last Ice Age in Ireland is dated to 12,000-10,000 BC.

Why are there limestone terraces in The Burren?  

Climatic changes during the formation of the Burren limestone led to rising and falling sea levels.  When the seas retreated for long enough, thin layers of fertile soil formed.  These in turn became submerged as the seas advanced again, and the process of limestone formation continued above the clay layers.  It is these thin layers of palaeosol that today separate the limestone layers, and that are responsible for the characteristic terraces of The Burren.  There are 9 palaeosol layers visible in The Burren today.  Palaeosol is softer and weathers at a much faster rate than limestone.  As it weathers at exposed faces, the overlying layers of limestone are undermined, fracture and break off under their own weight and also through erosion by glaciers.  The higher limestone layers, having been exposed for longer, show the greatest extent of breakage, leading to the "stepped" appearance of the terraces.

Why is The Burren only in the northern part of Co. Clare?

Due to movements in the Earth’s crust, the layers of limestone and shale slope downwards from northwest to southeast at an angle of about 2 degrees.  Because the glaciers moved generally horizontally, they stripped the shale away in the north, but at some point on their journey southwards, they began to slip over the shale rather than strip it away.  The line where the limestone slips under the shale marks the southern extent of The Burren.  This line extends from Doolin on the coast, around Slieve Elva, through Kilfenora and south of Corofin and Crusheen.  That explains why there’s such a spectacular change of scenery as you go along the coast road north of Doolin towards Fanore, for example, or from Kilfenora and Corofin towards Ballyvaughan.

What else is interesting about the geology of The Burren?

Imagine the glaciers as a very thick liquid flowing southward.  As they move, they fill all the low-lying areas and flow around the hills, stripping away and eroding the layers of rock in their path. (That’s why the limestone hills appear rounded, especially their north faces, which bore the brunt of the erosion.)  As the glaciers move, they fill the valleys under an ever-increasing depth of ice.  As it happens, before they had covered the highest points in the landscape, the climate changed.  It began to get warmer, and the glaciers stopped advancing.  At that point, if you looked down from a height directly over The Burren, you’d see a sea of ice with a few islands dotted here and there representing the highest points of the Burren landscape.  The Eskimos have a name for similar features that can be seen today.  They’re called “nunataks”.  These “islands” were the shale covered peaks of the hills that we can see today in the western part of The Burren, e.g. Slieve Elva and Poulacapple.  The landscape on Slieve Elva is completely different to that of the surrounding area.  It consists of poorly drained soil (shale is impervious to water) and an entirely different flora to the rest of The Burren.

What about the water?

Another interesting thing about the geology of The Burren is the effect that water has had since the limestone was exposed during the Ice Ages.  The glaciers didn’t advance and retreat at a uniform pace – there were stops and starts in the sequence.  When the climate started to warm and the advance of the glaciers was halted, meltwater flowed off and went to ground.  Where the water fell on shale, it flowed horizontally in a standard drainage pattern. Where it fell on limestone, however, it reacted chemically with the limestone and the process of erosion started.  Chemical erosion is the primary agent responsible for the characteristic grooves and channels that can be seen in the limestone today.  Collectively, these grooves and channels are known by a German word – karren.  Where the leading edge of the glaciers was stationary for a sufficiently long time, and natural faults in the limestone allowed, the water opened vertical fissures in the limestone.  These continued to widen and erode downwards (forming what are now known as sinkholes) until the water reached the chert and palaeosol layers separating the layers of limestone.  Chert doesn’t erode chemically in water, so the only way for the water to go was horizontally between the chert and limestone layers.  More erosion of the limestone just above the chert and along other natural faults in the rock led to the formation of tunnels carrying underground streams.  Today, it is estimated that there are hundreds of kilometers of underground streams and caves in the limestone beneath The Burren.  In many places, if you tap the limestone pavement, you’ll hear a hollow sound!

What are Clints and Grykes?

Enormous geological forces have acted on the limestone layers of the Burren during and since their formation.  They’ve been buried in turn under millions of tons of ice and water, and lifted and folded by the actions of vast continental plates.  The Variscan Belt of mountains running across mid-northern latitudes was formed about 300 million years ago when the two continental plates known as Laurentia and Gondwana collided to form the super-continent Pangaea.  It was this collision that caused the folds in the Burren limestone that are visible today, especially in the area of Mullaghmore. 

The enormous pressures associated with this activity caused the limestone to fracture in a generally North-South direction.  Subsequent depressurization between 300 m. and 60 m. years ago led to the development of additional, curved, fractures.  The action of rainwater since then has enlarged the fractures by erosion, and these are now to be seen as the characteristic “grykes” in the limestone pavement for which the Burren is famous.  Clints are simply the slabs of limestone between the grykes.

Are there caves in The Burren?

There are three types of caves in the Burren.  We’ve already discussed the sinkholes that formed where meltwater flowed off the face of the glaciers.  Where the water flowed into these sinkholes over a long time, they became big enough to form caves.  Some of the finest examples can be found near Slieve Elva and Poulacapple where water still flows off the edges of the shale caps on these mountains. Tunnel exits, where underground streams re-emerge, are known as risings.  In some places in The Burren where the water level has dropped or where water no longer flows through the tunnels, the risings are now dry and form caves.  Aillwee Cave is the most spectacular example of this type of cave in The Burren, and is well worth a visit. The third type of cave should properly be called a cavern, the defining characteristics being that it is big and has a vault-like roof.  Caverns are formed when water percolates down from the surface, eroding the roof of a cave to make it larger than the associated tunnel.  Another characteristic feature of caverns is often the formation of stalagmites and stalactites, although these can also be found in much smaller caves.  Spectacular stalagmites and stalactites can be seen in caverns in Doolin Cave, and also in Aillwee Cave.

What are Turloughs (pronounced “thurlocks”)?

Turloughs are disappearing lakes!  They can be formed in different ways, but essentially, they’re depressions in the landscape that fill with water (sometimes very quickly) following heavy rain, and drain through sinkholes or “swallow-holes” into underground streams.  There are many examples in The Burren. The biggest one is Carran Turlough, but there are others around Mullaghmore and in the eastern part of The Burren, known as the Gort Lowlands.  The word turlough is believed to derive from two Irish words - tuar loch - meaning “dry lake”.  There’s a distinctive flora associated with turloughs.  Cinclidotus fontinaloides is a black moss that grows on rocks, stone walls and trees at the maximum extent of the floodwater.  During the summer, the presence of this black moss is a sure indicator of a turlough.

What are Erratics?

As the ice retreated northwards, large boulders that had been carried south by the glaciers were occasionally deposited on the underlying limestone pavement.  Many of these have remained in place and can be seen to this day, for example on the coastal strip between Doolin and Fanore.  Most are limestone, but there are examples of granite boulders to be found in The Burren.  Granite is a much older rock than limestone (about 400 million years old) and therefore was deposited deeper than the deepest limestone layers.  So how did it come to be in The Burren?  To answer this question, we need to look north across Galway Bay.  Remembering that the rock layers slope downwards at about 2 degrees from northwest to southeast, it follows that at some point north of The Burren, the underlying granite layer will be exposed.  And so it happens!  The southern part of Co. Galway, the coastal strip along the north shore of Galway Bay, consists of pink Galway granite.  Boulders of this granite were transported by the advancing glaciers, and deposited in The Burren as they retreated.  And there they remain, sometimes on pedestals formed by eroding rainwater that has fallen in the 14,000 years since they were deposited.

Are the Cliffs of Moher in The Burren?

The short answer is “No”!  The Cliffs of Moher consist of Clare shale and other later types of mudstone that were deposited on top of the limestone that forms The Burren.  Shale doesn’t erode like limestone – it is brittle and breaks to a sharp edge, and it is the action of the sea pounding against the shale that is responsible for the formation of the Cliffs of Moher.  The limestone of The Burren slips under the Clare shales just north of Doolin and this marks the southern boundary of The Burren.

Why is there so much Archaeology in The Burren?

No evidence has yet been discovered to indicate that there were humans in Ireland before the last Ice Age.  After the end of the last Ice Age (about 12,000-10,000 BC) the climate began to improve.  By about 7,500 BC, there was sufficient vegetation and animal life to support small groups of humans, and the earliest evidence of human activity in Ireland dates to about this time – known as the Mesolithic.  It appears that people may first have come to the north-eastern part of Ireland while there was still a land bridge between there and Scotland.  No clearly identifiable Mesolithic objects or remains have been discovered in The Burren, but it is highly likely that people visited the area at that time.  It is clear that people had moved as far south as Co. Kerry by the Late Mesolithic with the earliest evidence from this area dating to about 5,000 BC.  The Neolithic period (4,000-2,400 BC) is when things really began to happen in The Burren, and today, this area has one of the densest concentrations of Neolithic remains in the country.  Many of these monuments are well preserved and clearly visible, and indeed the Neolithic portal tomb at Poulnabrone is one of the most-photographed and iconic images of The Burren.  Many other monuments and objects have been found from the Bronze Age (2,400-600 BC), Iron Age (600 BC – 400 AD), Early Christian Period (400-1169AD) and the Medieval Period from 1169AD.  A stunningly beautiful gold neck ornament dating to the Bronze Age (The Gleninsheen Gorget, now in the National Museum in Dublin) was found in a crack in the limestone pavement by a local farmer in 1932, for example.  There are also burial tombs, stone ringforts (known as cashels), very early churches and monasteries and castles from the Medieval period.