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Abstract: A landslide of 2.5 million m3 of sensitive glaciomarine sediments, predominantly silty clays, occurred at Mink Creek near Terrace, British Columbia (54°27′N, 128°37′W) some time between 1 December 1993 and 9 January 1994. We divide the landslide deposit into seven zones, distinguished on the basis of morphological characteristics. We interpret processes of flowing, spreading and sliding, often in succession, as the landslide retrogressed. The landslide is similar to other movements involving sensitive marine sediments, but is unique in that both flowing and spreading occurred, involving multiple rupture surfaces. Thus the landslide may be classified as a composite earth flow–spread. A decade of warm and wet climate preceded the landslide event. Since most global circulation models predict a warmer and wetter future for Terrace, more of these landslides may be expected. [Copyright &y& Elsevier]

Slopes in weakly cemented glaciolacustrine sediments in the Morkill River valley in the Canadian Rocky Mountains stand at up to 70°. Based on field and laboratory observations it appears that a contributing factor to instability is the softening of the soils by frost action and the leaching of calcite cement. Field density profiles demonstrated increased density and carbonate content with an increase in depth. Laboratory tests of carbonate content indicated a positive correlation between calcium carbonate and density in the glaciolacustrine sediments. The relationship was strongest in sands, in which leaching and dissolution were important components of softening. In clays, frost action was the dominant component of softening. Freeze-thaw tests showed a 50% decrease in strength after one cycle of freeze and thaw in the silts and clays.Key words: landslide, cemented, glaciolacustrine sediments, British Columbia.Les pentes dans les sédiments glaciolacustres dans la vallée de la rivière Morkill dans les montagnes Rocheuses canadiennes tiennent jusqu'à des angles de 70°. D'après des observations sur le terrain et en laboratoire, il semble qu'un facteur qui contribue à l'instabilité est le ramollissement des sols par l'action du gel et le lessivage du ciment de calcite. Les profils de densité du terrain ont montré une densité et une teneur en carbonate croissantes avec la profondeur. Des essais de teneur en carbonate en laboratoire ont indiqué une corrélation positive entre le carbonate de calcium et la densité dans les sédiments glaciolacustres. La relation était plus marquée dans les sables dans lesquels le lessivage et la dissolution étaient des composantes importantes du ramollissement. Des essais de gel-dégel ont montré une diminution de 50 % de la résistance après un cycle de gel et dégel dans les silts et les argiles.Mots clés : glissements de terrain, cimenté, sédiments glaciolacustres, Colombie Britannique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]