| The 1990 Eureka River landslide was an enlarged earth slide, in preglacial lacustrine sediment, with a volume of approximately 40 Mm 3, and a friction angle of 13.1 to 22.2°. The riverbed was thrust upwards by 20 to 23 m, forming a reservoir 8 km long. The 1995 Spirit River landslide was a reactivated and retrogressive earth slide, in till, with a volume of approximately 20 Mm3, and a friction angle of 7.9 to 15.9°. A 9 m pressure ridge formed a reservoir 2 km long. Valley gradients increase and channel gradients decrease upstream of both landslides. Precipitation was the likely trigger of the landslides. Increased streamflow due to land clearing was not apparent. Both landslides occurred within preglacial valley sediment; glaciolacustrine sediments overlie and underlie till. Each deposit is prone to slide. Landslides in or below the till form dams. Both landslides broke the streambed armour thus the streambeds are susceptible to erosion. |
