Rockfalls are a constant problem along transportation routes through rocky terrain across Canada and have also impacted on buildings located below bedrock slopes. Debris avalanches and channelised debris flows form a group of landslides that are characterised by the rapid flow of saturated materials in steepland terrain. Typically, debris avalanches and debris flows consist of boulder and gravel size clasts that are transported in a finer grained slurry. A debris avalanche occurs when a saturated mass fails on an open slope and does not become channelised. It is differentiated from a channelised debris flow which occurs when a saturated mass of debris moves downslope confined in a steep stream channel.
Debris avalanches are common in forested steeplands.
Landslide volumes generally range from 20,000 to 60,000 m3. Debris flows are frequently generated by the channelisation of an initial debris avalanche triggered in the steep upper slopes of a watershed. They may also be triggered by the impact loading of stream bed materials by rockfalls or falls of glacier ice. Debris flows and debris avalanches occur widely in the Cordillera of western Canada. They also occur in the Appalachian and Laurentian Mountains of eastern Canada where their occurrence is invariably linked to heavy rains.