The Weathering Process | Surface Limestone Features | Underground Limestone Features
The Cycle of Erosion | Human Settlement in the Burren
The main example of a limestone (or 'karst') region in Ireland is the Burren region in north Co. Clare. The term 'karst' originated in a region of Slovenia/Croatia, near the Adriatic Sea, and it is used to signify an area of limestone in which the rock is exposed at the surface of the landscape and where there is mainly underground rather than surface drainage. In studying the Burren region you must understand the weathering or denudation process, the surface and underground features, and the cycle of erosion there. This study is completed with an examination of how human settlement has interfered with this unique landscape over the years.
The Weathering/Denudation Process (carbonation)
Weathering or denudation in a limestone region is affected by carbonation, and this process is fundamental to the understanding of the region's physical geography. Limestone, or calcium carbonate (CaCO3), is a sedimentary rock formed by the compressing of the remains of dead sea creatures.
Weathering of the rock is made easy by the fact that limestone contains bedding planes (horizontal cracks) and joints (vertical cracks) allowing water to pass through the rock. The chemical weathering of limestone, or carbonation, occurs when the rock is attacked by rainwater. The chemical equation for this process is CaCO3+ H2CO3 = Ca(HCO3)2, i.e., Limestone + Carbonic acid (rainwater) = Calcium Bicarbonate (soluble limestone).
Surface Limestone Features
The most common surface feature to be found in the Burren is limestone pavement with clints (slabs of rock) and grooves caused by weathering of the surface joints (grikes). Other surface features to be studied include swallow holes (through which surface water disappears underground), dry valleys (created by the loss of surface water), karrens (tiny weathered hollows), uvalas (created by the joining of swallow holes), poljes (when uvalas join), dolines (a closed hollow) and turloughs (seasonal pond). All of these features result from carbonation.
Underground Limestone Features
Underground features are formed from water, for example by streams flowing down through the permeable rock. Constant weathering of the limestone causes the bedding planes to be enlarged sufficiently to form an underground cave. The cave then becomes home to many distinctive features. Evaporation of the water seeping through the cave leaves behind deposits of calcium carbonate, referred to as dripstone. Dripstone hanging from the ceiling creates stalactites, while stumps developing on the cave floor are called stalagmites. When they both join, a column or pillar is formed. A curtain is yet another dripstone feature. When writing about limestone features (surface and underground), specific examples in the Burren should be given and diagrams should be labelled.
The Cycle of Erosion
The cycle of erosion in limestone (karst) regions goes through three stages: youth, maturity, and old age. In the youthful stage, impermeable rock is removed and the limestone is hit by carbonation to form features such as limestone pavements and swallow holes. In maturity, carbonation has progressed to form a dry valley, dolines, turloughs, caves, etc. The Burren, Co. Clare is at this stage presently. During old age, weathering has removed so much of the limestone that only the rock with greater resistance to attack remains. These hills of rock are called hums. Knowledge of the development of all three stages is advised.
Human Settlement in the Burren
To complete an understanding of the uniqueness of the Burren, you must examine how the development of this region has evolved. Tourism has been the main reason for development in this 'rocky place' of approx. 450 square miles. Throughout the 1990s, plans for the building of an interpretative centre in the Burren caused considerable conflict. These plans were finally rejected in March 2000. However, it is still necessary for students to be able to discuss arguments for and against such a development. A natural attraction in the Burren, apart from the limestone features, is the rare Alpine, Mediterranean and Arctic plants growing there. Manmade attractions include megalithic tombs, stone raths, churches and high crosses. Also, the region is steeped in history.
An in-depth account of what a 'Karst landscape' is, plus other articles of interest.
This is the home page of the Burren action group.
Some general information here about the Burren.