Use of multitemporal airborne lidar surveys to analyse post-failure behaviour of earth slides

Two helicopter-borne light detection and ranging (lidar) surveys were conducted in August 2004 and May 2005 on a 2 km(2) earth flow that was totally reactivated in late winter 2004. Shaded-view maps and differential analysis of terrain models from the two surveys allowed residual movements, as well as rupture and accumulation features over the slope, to be assessed and mapped for the period between 2004 and 2005. In particular, this analysis has shown that residual movements involved about 20% of the whole landslide area. Retrogression of the crown zones, with a depletion estimated in the order of 20 m, was coupled with a more than 10 m advancement of the deep translational slide affecting earth and rock materials in the source area. This has resulted in an apparent uplift of more than 15 m. Down slope, the upper accumulation lobe sector was lowered by about 10 m because of depletion and the progressive decrease in water content. This analysis proved the usefulness of lidar surveys for analysing post-failure behaviour of this type of mass movement.