The past two million years have largely been characterised by Ice Ages and interglacial periods (when the ice retreated). The average duration of interglacials was as long as 100,000 years so it is possible that we are now living in an interglacial and that the ice sheets will return!
Approximately 20,000 years ago, ice sheets, thousands of feet thick stretched from the North Pole to Europe covering much of Ireland (except for some southern areas). This created an Ice Age or glacial period in Ireland. A glacier is a river of ice, rocks and soil that is formed when snow is flattened by more snow forming grains of ice called névé. These are then pressed together forming sheets of ice. Glaciers are usually formed on high ground and then move downhill creating a valley in the landscape picking up rocks and soil as they move. This Ice Age was caused when the temperatures in the summer were not warm enough to melt the snow and ice that built up over the winter gaining in mass over the years. Canada, most of the United States and northern Europe were all covered in ice. Some parts of the world such as Greenland and Antarctica are still going through an Ice Age. The sea level around the world dropped so much that Ireland was joined to Britain and the rest of Europe when some of the sea between them disappeared exposing the seabed.
Ireland had very little if any animals or plants at that time. But around 15,000 years ago the ice gradually began to disappear, Ulster was the last area in Ireland to be covered in ice and once the ice began to melt animals crossed over from Britain across land bridges that had been left behind after the drop in sea level. A freshwater lake was formed between the ice sheets up in the north in Ulster and the land bridge down south. Many grasses and trees were the first bit of life to take hold and then Giant Deer and other animals arrived over the land bridge in the south. Humans also crossed this bridge into Ireland about 9,000 years ago.
Gradually the sea level rose due to the melting ice and the sea floor that had been exposed before was covered over again, as was the land bridge. The landscape was totally changed as the glaciers formed new mountains and lakes. The weight of the glacier over Ireland caused it to be squashed a little and pushed down but this has been rising again by about 2mm every year. Then, around 14,000 years ago, Ice in Ireland had eventually melted.
Doon Lough, Conor Pass, Dingle, County Kerry.
Rock pavement at lip of Doon Lough, Conor Pass, Dingle. The scratches visible on the rocks are evidence that the corrie basin was scooped out during glaciation. Rocks at the base of an ice sheet flowing outwards left distinct scrathes on the hard sandstone. Such features are vulnerable to damage and the Irish Geological Heritage Programme is defining the most important geological sites across the country for protection as NHAs or as county geological sites.
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