Ancient Dunes and Storm Beach
Besides its scenic beauty and the picturesque Min Aird Castle, which watches over the bay, Cill Mhuire Bay is of great geological interest for two main reasons. Here 380 million year old fossilised sand dunes can be seen in the cliffs and it contains one of the finest storm beaches in Ireland.
In the Devonian period rivers flowed south across a large desert and carried sands and coarse sediments. Crescent-shaped sand dunes were formed out of it. Subsequently consolidation and cementation built the pale yellow Kilmurry Sandstone. This sandstone is a unit of the Old Red Sandstone that forms much of the Slieve Mish mountains and those seen on the Iveragh Peninsula. The rocks were deposited as sand-dunes as large as those in the Sahara Desert today, because they contain alternating layers of sediments in a pattern called ‘herring-bone cross-stratification’. This layering is to see in the rocks in the cliffs.
A storm beach is created by particularly fierce waves. The resultant landform is often a very steep beach (up to 45°) composed of rounded cobbles, shingle and occasionally sand. The stones usually have an obvious grading of pebbles, from large to small, with the larger diameter stones typically arrayed at the highest beach elevations.
At this location large blocks of Kilmurry Sandstone have become rounded by the action of the waves and from knocking against each other. They now resemble large eggs. This process lasted over many hundreds and possibly thousands of years. It seems incredible given their size that the force of storm waves could move them, but they have been thrown to the back of the beach where they form a ridge called a storm beach.
List of sources:
Onsite Infoboard: The Roadside Geology of West Kerry
Your tasks to log this earthcache:
1. Describe the disposal of sediments (pebbels, sand, "eggs", shingle), as they appear at the location seen from the shore.
2. Describe the large boulders in size, color and texture. There is one special thing.
3. Min Aird Castle is build of which kind of rocks (see infoboard).
4. Optional: try to add a photo or drawing to your log from the herring-bone cross-stratification in the cliffs.
5. Optional: Please add a photo of your stay to your log. (this is no obligation, but it would give us a pleasure. Be creativ ;-)
You can log your visit as a found directly after sending your answers. You will get a response in any case ;-)
Have fun! Viel Spaß!