What is karst?


Karst is a term used world-wide to describe the distinctive landforms that develop on rock types that are readily dissolved by water. In Ireland, limestone (composed of calcium carbonate) and to a lesser extent dolomite (calcium and magnesium carbonate) are by far the most widespread rocks that show karst features. There is also a small outcrop of a younger softer rock also made of calcium carbonate – the chalk of Co. Antrim – which shows some of the features characteristic of karstic terrains. In other parts of the world, highly soluble rocks such as gypsum (calcium sulphate) and halite (common salt or sodium chloride) are abundant and they also exhibit karstic landforms

Conical karst hills in the Philippines (Ken Gardner)

The word karst is derived from the Serbo-Croat word krs and the Slovenian word kras meaning stony bare ground. The Kras is a limestone region, now a part of Slovenia and Croatia, in which the distinctive karst landforms are exceptionally well developed.

Karstified limestones cover approximately one tenth of the land surface of the Earth, but some 25% of the world’s population lives in these regions – for example southern China, large areas of central and southern Europe and much of central America. As the map on page x shows, half of the Republic of Ireland is underlain by limestones, many of which are karstified.

Typically, karst regions lack rivers and other surface waters because the rain is swallowed up by fissures and conduits in the rock and then flows as underground streams in caves. Eventually the waters return to the land surface, often as large springs. Karst areas are indicated by a general absence of permanent surface streams and the presence of swallow holes and enclosed depressions. The water is usually all underground in solutionally enlarged channels, some of which are big enough to be termed caves.

Martel Stalactite, Marble Arch Caves (Robert Thomson)

Karst regions have always been important to human societies. In prehistoric times they were used as refuges and are thus very important for archaeological remains – the cave paintings of Lascaux in France and of Altimira in Spain being famous examples. Karst rocks also often contain large quantities of water which are widely used for water supply.

Tourism is one of the most rapidly growing industries world-wide and karst regions, in many cases with spectacular scenery and natural curiosities such as caves, attract large numbers of visitors.

Limestone pavement in the Burren with a turlough in the background (Donal Daly)

Some well known karst areas and features:

• The Greek islands
• Dordogne, Vercors and Tarn areas of France
• Pinnacle karst of the Guilin area, southern China
• Mammoth Caves, Kentucky, USA
• Postojna Caves in Slovenia