Slope Failure Hazard in the Atlantic Provinces: A Review

Abstract

Slope failures present a common hazard throughout the world and have considerable impact on transportation, forestry, coastal and urban development, and other human activities. Although little recognized in much of Atlantic Canada, mass movements have resulted in as many as 71 fatalities in Newfoundland. Due to the high relief of Newfoundland, rockfalls have caused several fatalities and damage to property is frequent. In the Ferryland disaster of ca. 1823, 42 fishermen were reportedly killed when a cave roof collapsed onto them. Debris torrents and flows are widespread particularly in areas of higher relief in Newfoundland and Cape Breton Island, and tend to be most hazardous for highway engineering and community development. Typically, a thin cover of till or colluvium overlies a steeply sloping and polished bedrock substrate. Failure is generally triggered by rainfall events. Rotational slumps of glaciomarine clays are particularly evident along the major river valleys of Labrador and are an important consideration for hydroelectric development such as along the lower Churchill River. Numerous sackungs have been identified, notably in the ultramafic rocks of western Newfoundland. In other areas of Atlantic Canada, earthflows frequently affect transportation routes and commonly involve movement of saturated sediment during spring thaw. Along the Gulf of St. Lawrence and Northumberland Strait and the Bay of Fundy coastlines, the combination of friable Carboniferous and Permian sediments, glaciotectonic activity, frost wedging, and coastal erosion has resulted in numerous small failures, along with incremental retreat of coastal cliffs. Ongoing climate change will have an impact on slope failure activity. The pattern of increasing summer frequency and intensity of thunderstorms and hurricane events, increased winter precipitation in some locations, and more erratic freeze-thaw events during late winter and spring, will result in an increase in debris torrents triggered by precipitation, and rockfalls triggered by freeze-thaw. Human utilization of coastal areas for recreation and residential construction is also increasing both the frequency and hazard of slope failures across Atlantic Canada.