Frontal advance of turf-banked solifluction lobes, Kluane Range, Yukon Territory, Canada

Humus horizons associated with thirteen solifluction lobes on a single slope were radiocarbon dated at fixed distances behind the risers, as well as ahead of the lobes. The dated horizons, together with stratigraphic observations of planar discontinuities inside the lobes and shallow burial of vegetation ahead of the lobes, all suggest rapid advance of lobe fronts. We infer that lobe advance at this site results from slow accumulation of soliflucted material behind a relatively rigid riser, progressive steepening of the riser and build-up of stress, and finally rupture of the front and its collapse onto the slope. Rebuilding of the lobe usually then takes place. The time for a full cycle of development is estimated to be in the order of a few hundred years. Long-term frontal movement appears inversely related to lobe size, and is mainly controlled by soil moisture and sediment characteristics. These findings call into question the usefulness of solifluction lobe advance rates for paleoclimate reconstructions, at least at this site.