Landslides and geotechnical properties of volcanic tuff on Mount Cayley, British Columbia

major rock slide and debris flow occurred on Mount Cayley, in June, 1984. 3.2 million cubic metres of volcanics travelled 2.0 km down Avalanche Creek at velocities up to 35 m/s to dam the confluence of Avalanche and Turbid Creeks. The breaking of the landslide dam caused an extremely fast debris flow. The velocity of the debris flow and associated wind gusts, up to 64 m/s, caused superelevations, hurled rocks and wood through the air, uprooted trees and spattered mud 16 m up trees.;Volcanic tuff constitutes the basal rupture zones of the 1963 and the 1984 rock slides. The tuff has a low dry density, 13.6 KN/m;Two major modes, Tuff type and Dacite type, of slope movement are recognized. Tuff type landslides involve Units 4 and 5 of the volcanic rocks, they transport deposits with a special grain size distribution with D50 value less than 5 mm. Dacite Type landslides involve Units 2 and 3 of the volcanic rocks, they transport deposits with D50 value larger than 10 mm.;The Turbid Creek fan has been built by eight prehistoric episodes of slope movement from Mount Cayley. A new episode of slope movement started in 1963 and is going on at present. Three unstable slopes are recognized on Mount Cayley. Their sizes, movement paths, velocities and impacts on the environment are discussed.;The 1963 rock slide began at the head of Dusty Creek, and terminated at the new confluence of Dusty and Turbid Creeks. About 5...