Legacy of Water - Deposits of Lakes and Rivers
As the glaciers melted away during the end of the last very cold period, the deposits they left behind were readily eroded by rivers. Gravel and sand were carried by streams and redeposited as fans where the streams entered larger glens; particularly good examples can be seen on the east side of Glen Roy at Brunachan and the Allt Reinich. Where the rivers entered lakes, deltas were formed as their sediment loads were dropped suddenly in the standing water. At Fersit, a delta was built out across buried ice which later melted, causing collapse of the sediments and the formation of large depressions called kettle holes (see photo p26). When the Parallel Road lakes were in existence, mud carried into them settled out as layers of silt and clay on the floor of Glen Roy, Glen Gloy and Glen Spean. Such laminated silt and clay can be seen today in road cuttings, for instance along the public road in Glen Roy. As their discharges and sediment supply varied, the rivers at different times built up thick deposits of sand and gravels on the floors of the glens, or incised down into these deposits forming extensive suites of river terraces, for example between Roy Bridge and Spean Bridge in Glen Spean.