The Collapse of Solifluction Lobes as a Factor in Vegetating Blockfields

ABSTRA(3T: The development of soil and vegetation in blockfields through normal processes is very slow. It is surprising, therefore, to find in the Ruby Mountains of southwest Yukon Territory, tongues and islands of vegetation occurring amidst certain blockfields. The collapse of solifluction lobes from upslope is suggested as the mechanism responsible. The lobes pass from the more gentle solifluction slope of the alb onto the steeper slope of the blockfields, and eventually become unable to maintain themselves because of: steeper slope, change in composition of vegeta- tion, and deeper active layer. Once the lobes do collapse, they flow downslope carrying with them clumps of vegetation which may become established somewhere along the mud-flow channel or levee. In this way, small outposts of vegetation are created and speed up a process which would otherwise take indeterminately longer.