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Destructive landslides are common in west central British Columbia. Landslides include debris flows and slides, earth flows and flowslides, rock falls, slides, and avalanches, and complex landslides involving both rock and soil. Pipelines, hydrotransmission lines, roads, and railways have all been impacted by these landslides, disrupting service to communities. We provide examples of the destructive landslides, their impacts, and the climatic conditions associated with the failures. We also consider future landsliding potential for west central British Columbia under climate change scenarios.

A reanalysis of the varve chronology from hydraulic piston sediment cores was carried out to establish better uncertainty estimates on ages of prehistoric debris-flow deposits (DFDs) in the last 4000 yr. Saanich Inlet is an anoxic fiord located in southeast Vancouver Island near the city of Victoria, British Columbia. It contains annually laminated (varved) marine mud deposited in anoxic conditions. Interlayered with these Holocene varves are massive layers of coarser sediments deposited by submarine debris flows. It has been previously interpreted that these flows were induced by earthquake shaking. Two of the DFDs correspond to known earthquakes: A.D. 1946 Vancouver Island (M 7.3) and the A.D. 1700 Cascadia plate-boundary subduction earthquake (M 9). Based on varve counts

Eight piston cores of sediment spanning the last 1500 years were collected from Saanich Inlet, an anoxic fiord on southern Vancouver Island, to obtain information on sedimentation and prehistoric earthquake activity. The cores consist mainly of fine-grained varved sediments, but include massive layers deposited by subaqueous debris flows. The debris flows may have been triggered by earthquakes or by the buildup of fine sediment on the walls of the inlet. Cesium-137 and 210Pb data, 14C ages, and varve counts were used to date and correlate massive layers in the eight cores. The uppermost massive layer in two cores may record a magnitude 7.2 earthquake that occurred in 1946 near Comox, British Columbia, 200 km north-northwest of Saanich Inlet. Seven older layers are found in two or more cores and are about 200, 440, 550, 800–850, 1050–1100, 1100–1150, and 1450–1500 years old. Two of these older layers may correlate with previously documented earthquakes in the region. There is an average of one massive layer per 116 varves in the core with the greatest number of such layers, which is broadly consistent with the expected periodicity of moderate to large earthquakes in the region, on average, one earthquake producing local Modified Mercalli Intensity VII or VIII per century. Saanich Inlet may contain a proxy record of all moderate and large earthquakes that have affected southwestern British Columbia during Holocene time, but some of the massive layers do not appear to correlate from core to core and undoubtedly are nonseismically generated deposits.

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