The source of the River Slaney is Lugnaquilla peak in the Wicklow Mountains. Its long journey to Wexford town takes it through many villages, landscapes, and across different bedrock types. You can divide the River Slaney into sections according to the bedrock it flows over. For example, it cuts through metamorphic rocks, including slate, schists and phyllite, in Bunclody, and igneous rocks like granite in Baltinglass.
The shapes of rivers are influenced by many factors including slope, bedrock type and strength, and the size of the sediments the river carries. Like most rivers in Ireland, the Slaney’s development is linked to the last ice age. As the ice melted, a large flow of meltwater cut and carved the bedrock of the ancient river channel, changing the slope and shape of the rivers. Today, the Slaney can only move small items, from silts to cobbles, but when the ice was melting, the amount of water flowing through the Slaney would have been ten times greater – enough to move boulder-sized materials.
Evidence of the last ice age can be found along the course of the river. Different landforms of glacial origin can be seen, such as meltwater channels, mounds made up of unsorted glacial sediments of different sizes, called hummocks, old river floodplains made up of a mixture of sediments, called terraces, and other glacial sediments that were flattened and cut by the river.