Subsurface Movement on Solifluction Slopes in the Ruby Range, Yukon Territory, Canada: A 20-Year Study

Abstract

A 20-yr investigation of soil movement rates on four slopes in the Ruby Range, Yukon Territory, has revealed greater differential movement at depth than at the surface under certain conditions. This type of movement, found primarily on a southeast-facing slope with welldeveloped solifluction lobes and complete vegetation cover, typically produces profiles that are convex-concave downslope rather than simply concave downslope as commonly reported in the literature. The movement profiles comprise three sections: (1) top 20 cm where greatest total movement occurs but there is little differential movement; (2) depth of 20 to 50 cm where greatest differential movement occurs; and (3) depths below 50 cm where little movement takes place. Rates of surface movement over the 20-yr period range from 0.53 to 2.05 cm yr-~ and total volumetric displacements range from 18.9 to 67.3 cm3 yr-'. Movement occurs in early summer by soil flowing between the turf mat and frozen ground as well as possibly by en masse movement of the entire surface through discrete shearing at a depth of 30 to 50 cm.