Glenmalure is the longest U-shaped glacial valley in Ireland or Britain, stretching 20 kilometres from the northwest to the southeast. U-shaped valleys were formed by glaciers, wearing away rocks and soils as they moved through existing V-shaped river valleys. The U-shape was formed as they widened the valley floor and made the sides steeper.
If we could travel back 25,000 years, we would see breathtaking 750-metres-tall glaciers. Everything would be covered by ice and only the highest peaks would be visible above the glaciers. The weight of this ice combined with the scratching of the rocks it carried against the base and sides of the valleys it travelled through, carved and polished the landscape creating the smooth surfaces and U-shape Glenmalure has today. The groups of broken rocks on the slopes, called scree cones, and the lakes evidence this area’s glacial past. Glaciers began to melt about 22,000 years ago, and from 10,000 years ago the plants and animals we see today started to grow and arrive. Soils were formed as the rocks and sediments left behind by melting glaciers were further broken down and plant materials were gradually added as plants arrived in the valley.
Glenmalure’s important mining heritage can be seen in the building ruins and spoil heaps. The mines in Glendalough, Glendasan, and Glenmalure were Ireland’s most important producers of lead in the 1800s. Many beautifully coloured minerals were found within the lead and copper ores extracted from these mines.