Wednesday, June 15, 2016


Ireland was once at the bottom of the ocean. Yes, that's right, Neptune, mermaids, singing crabs, and all that (well maybe not so much singing). Because of our shelled friends, this resulted in an accumulation of calcite or calcium carbonate (CaCO3) in the material that fell to the ocean floor. Limestone is a sedimentary rock, which is a rock that is formed from deposition of sediment that is ultimately compressed and cemented together from pressure. In the case of limestone the pressure exerted comes from the ocean water. The deeper the water the greater the pressure. Limestone in Ireland formed during the Carboniferous period (360 to 300 million years ago). The climate was  tropical in Ireland at this time (think Bahamas!). In addition to calcite, other minerals were present in the sediment giving the rocks that formed a grayish color as shown in the pictures below. As Ireland is obviously no longer under water these rocks are now at the surface and predominate the countryside. They can be seen in both their original position (hillside) as well as used for rock walls that act as confines of pastures for grazing animals.

Limestone hills and walls on the road south of Kinvarra, Co. Galway, Ireland.

A feature that goes hand in hand with the presence of limestone are "karsts." These form as a result of dissolution (minerals dissolving from the presence of water). This process creates "karst landscapes" where the rocks that have spaces in between where the less soluble (more stable) rocks remain. This is demonstrated in the picture below.

Poulnabrone Dolmen in Co. Clare, Ireland.

However, one of the most exciting features of karst landscapes are the caves! Limestone caves in Ireland have many interesting features. Where the calcium carbonate dissolves, it forms different morphological features that you may be familiar with from grade school geology,  namely stalactites and stalagmites. Before these formations reach their identifiable stages, there must be accumulation of calcite, which can look a bit messy initially.

Calcite (calcium carbonate) deposits from limestone in Aillwee Cave.

More calcite deposits on the Aillwee Cave wall.

...And given the right conditions these deposits can form some amazing features inside the cave!

Doolin Cave Co. Clare, Ireland

This impressive 24 foot calcite stalactite is the longest in the Northern Hemisphere. It was not discovered until 1952, when two brave (and slightly nutty) members of a caving club decided to crawl through a small opening and tunnel in complete darkness (to save their torch fuel). Their efforts were rewarded though as you can see in the picture above.

Directly below this feature should be an equally impressive stalagmite. However, due to geological shifting the mass did not accumulate vertically. Instead some sliding occurred and what you see below is the result of thousands of years of calcite accumulation. This feature is only about a foot tall. The sloughing off to the right is the mass that should have formed the stalagmite.

Doolin Cave Co. Clare, Ireland

Knowing a bit about the scientific processes behind the geology just adds to the wonder of this country. The limestone in western Ireland creates an austere yet beautiful landscape both above and below ground. It was impressive to find plants growing in these formations, but as always, nature finds a way! Tune in next week for another look at geology in Ireland...The Cliffs of Moher!