Geological history of the Copper Coast

The Copper Coast Geopark, Co. Waterford, Ireland: 460 million years of Earth history

During Ordovician time, about 460 million years ago, North West of Ireland was located on a continent called Laurentia. South East of Ireland and the Copper Coast were located near the South Pole, on the continental margin of the micro-continent called Avalonia. Between lay the Iapetus Ocean. The first rocks to form on the Copper Coast were mudstones and shales created by the erosion of the continent and deposited on the ocean floor.



Andesitic eruption at Mt Vesuivuis, Italy

Gradually, the two continents were getting closer while the Iapetus Ocean was closing. Subduction was taking place, generating volcanism both on the south east and north western part of Ireland. Molten magma was slowly moving up from the deep within the earth towards the ocean floor, puncturing into water saturated sediments. Lava spewed out across the ocean floor forming sheets of andesite.

About 455 million years ago, volcanism eased for a while allowing larvae and various types of shellfish to colonise the shallow seas around the area. Generations of shellfish lived and then died. Shells were broken and pulverized, slowly building limestone layer upon layer.

Around 450 million years ago, subduction was then reactivated and the volcanism became more acidic, thus more explosive. Huge volumes of sticky, pale grey rhyolite lava, ash and debris were generated and spread over hundreds of square kilometres of the ocean floor. Sea water and the volcanic fluids flew through the existing porous layers and “stew”. Slowly the rocks changed colour and texture and their composition changed from original grey they become variegated shades of white, orange, green, and purple.

The Copper Coast started out at the South Pole and whilst all the above was going on locally; the landmass carrying the Copper Coast had been slowly drifting north towards the Equator and the other continent Laurentia. Eventually they collided, about 400 million years ago. Under the pressure, all the sedimentary and volcanic rocks previously formed under water were slowly crumpled into folds, some shattered and broken along faults; blocks were jumbled up, displaced and brought to the surface.

During Devonian time, about 360 million years ago, the coast became a dry land virtually on the Equator. Rivers snaked their way to the sea from the distant mountains to the north. Storms gathered and broke on the mountains. Huge flash floods raced down, carrying boulders, coarse gravels, and dropped their load on the way. As the rush of water eased, thin layers of finer material (sand, silt and mud) were dropped. The water flew away into the sea and the land was baked by the sun: the desert was laid. This cycle of searing heat and flash floods built sheet upon sheet of red-brown sandstone and conglomerate.

 

 

 

 Over the next 358,000,000 years, many events happened but little was recorded in the rocks along the Copper Coast other than the buckling and tilting and upending of the desert rocks and perhaps the origin of the copper which has given its name to the coast.

Then the Ice Age arrived, about 2 million years ago. Glaciers, most born in the midlands, grinded their way out gouging out paths, crushing and pulverizing the rocks into boulders, sand and mud. Global warming occurred and the glaciers started to melt, dumping their loads of boulders, sand and mud across the land. The ice sheets and glaciers started to advance again and retreated, the cycle of pulverizing and dumping continued, thus depositing several layers of glacial till-boulder clay. Finally the ice retreated.

Today, the sea recycles most of the rocks along the coast.