A pre-historic pseudo-circular rock-slope failure at the northern edge of Dawson City, Yukon occurs in altered ultramafic rocks. The middle section of the landslide debris continues to move down-slope, as is evident from sheared trenches, stretched roots and split trees along its edges, and a steep snout exposing fresh material. Dendrochronological analysis demonstrated that the split trunk of one tree has displaced over the last 40 to 45 years at an average movement rate of 4.5 cm/year. This moving section of the debris could be characterized as a rock glacier or as an earth flow, although our present observations and measurements do not confirm either mechanism. A block upslope from the headscarp of the landslide exhibits signs of recent movement. To assess the movement rate of the different sections of the landslide in the future, a monitoring array was set up and an initial set of measurements was taken in July, 2006.
