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.

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.

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