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DEVELOPMENT OF SOLIFLUCTION LOBES, KLUANE RANGE, YUKON TERRITORY

KINNARD, CHRISTOPHE  Geography Department, University of Ottawa.
Lewkowicz, Antoni G  Geography Department, University of Ottawa.

Solifluction lobes are abundant above treeline on an alpine plateau located near Kluane Lake, Yukon Territory. On a west slope (1800 m a.s.l.), lobes typically increase in size downslope, evolving from small sorted steps near the slope crest to extensive complexes with multiple fronts at the foot. In August 2001, 13 solifluction lobes were excavated to conduct stratigraphic observations and collect humus buried beneath the lobes (Figure 1). 25 humus samples were radiocarbon-dated to obtain long-term rates of lobe advance. In the spring of 2002, surface movement was monitored on five solifluction lobes using repetitive surveying of surface targets, while groundwater levels and thaw depths were measured on these lobes and along the entire slope. In addition, 250 lobes were mapped, and their morphometry measured.

These results were used to construct a simple model of lobe development, in which frontal advance results from the slow accumulation of material behind a comparatively rigid front, until a threshold of instability is reached and rapid advance occurs by shearing. Lobes across the study slope represent different stages of this cycle and inter-lobe comparison and climatic interpretation of changing rates must deal with the lag time of this episodic frontal movement.



The downslope increase in moisture availability is the primary cause for the spatial gradation of landforms observed on the slope: increased moisture during autumn freeze-back and spring thaw cause larger surface movements downslope while the vegetation cover, which is best developed in the moist areas downslope, causes an increase in slope resistance, allowing lobes to grow larger before collapse occurs. Spatial analysis of lobe dispersion suggest that the population of solifluction lobes represents an organized succession of wave-like benches, whose wavelength and amplitude are controlled by the downslope increase in solifluction activity.

REFERENCES
Alexander, C.S. and Price, L.W., 1980, Radiocarbon dating of the rate of movement of two solifluction lobes in the Ruby Range, Yukon Territory: Quaternary Research, v.13,p. 365-379.



Ballantyne, C.K., 1986a, Late Flandrian solifluction on the Fannich Mountains, Ross-shire: Scottish Journal of Geology, v.22, p.395-406.



Benedict, J.B., 1970, Downslope soil movement in a Colorado alpine region: rates, processes, and climatic significance: Arctic and Alpine Research, v.2, p.165-226.



Elliot, G. and Worsley, P., 1999, The sedimentology, stratigraphy, and 14C dating of a turf-banked solifluction lobe: evidence for Holocene slope instability at Okstindan, northern Norway: Journal of Quaternary Sciences, v.14, p.175-188.



Hugenholtz, C.H. and Lewkowicz, A.G., 2002, Morphometry and environmental characteristics of turf-banked solifluction lobes, Kluane Range, Yukon Territory: Permafrost and Periglacial Processes, v.13, p.301-313.



Matsuoka, N., 2001, Solifluction rates, processes and landforms: a global review: Earth-Sciences Review, v.55, p.107-134.



Matthews, J.A., Ballantyne, C.K., Harris, C., and McCarroll, D., 1993, Solifluction and climatic variations in the Holocene: discussion and synthesis: In Frenzel, B. (Ed.), Solifluction and Climatic Variation in the Holocene. European Science Foundation, Stuggart, p. 339-361.



Figure 1. Excavation of a solifluction lobe to uncover the buried humus horizon.


Figure 2. Downslope variation in lobe frequency. Some lobes from the upper slope (in grey) have been omitted from the analysis because mapping was inconsistent in that area, while three lobes on the lower slope and three lobes on the upper slope were omitted because they could not be included in the moving average.


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