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Inishmore cliffs and karst landscape from Dun Aengus

Inishmore cliffs and karst landscape from Dun Aengus

Inishmore (Inis Mór) is the largest of the Aran Islands in Galway Bay in Ireland and has an area of 31 km2 (12 sq mi). Inishmore has a population of about 840,...
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Inishmore (Inis Mór) is the largest of the Aran Islands in Galway Bay in Ireland and has an area of 31 km2 (12 sq mi). Inishmore has a population of about 840, making it the largest of the Aran Islands in terms of population and largest island off the Irish coast with no bridge or causeway to the mainland. The island is famous for its strong Irish culture, loyalty to the Irish language, and a wealth of Pre-Christian and Christian ancient sites including Dún Aengus, described as "the most magnificent barbaric monument in Europe" by George Petrie.

The island is an extension of the Burren. The terrain of the island is composed of limestone pavements with crisscrossing cracks known as "grikes", leaving isolated rocks called "clints". The limestones date from the Visean period (Lower Carboniferous), formed as sediments in a tropical sea approximately 350 million years ago, and compressed into horizontal strata with fossil corals, crinoids, sea urchins and ammonites. Glaciation following the Namurian phase facilitated greater denudation. The result is that Inishmore and the other islands are among 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 island overrun by ice during this glaciation. The impact of earlier Karstification (solutional erosion) has been eliminated by the last glacial period. So any Karstification now seen dates from approximately 10,000 years ago and the island Karst is thus recent.

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 sub-terrainean drainage.

Dún Aonghasa (anglicized Dun Aengus) is the most famous of several prehistoric hill forts on the Aran Islands. It lies on Inishmore, at the edge of a 100 metre high cliff.
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