An Unstable Landscape
Glacial erosion produced steep-sided glens, some of which are unstable. In some cases the result is slow, deep downhill creep of the rocks. In others, the instability results in landslips. When the Parallel Road lakes drained, a great weight of water was removed very quickly from the glen sides, causing them to be particularly unstable and prone to landslipping. Landslips formed in this way are well displayed in Glen Roy, for example near Braeroy. Catastrophic emptying of modern reservoirs is known to be accompanied by small earthquakes, and it is probable that there were quakes as the Parallel Road lakes were drained.
Although the hill slopes are now mostly stable, the public road in Glen Roy needs to be repaired from time to time in response to local slips, washouts and debris flows. Modern river erosion is also locally active in undercutting older river terraces.
The sheets of muddy debris, sand and gravel left behind as the ice melted away continue to be eroded, as is clear from the spectacular river cliffs that dissect a large outwash fan near Braeroy, and by the ever shifting course of the river nearby.