Quantitative assessment of the complexity of talus slope morphodynamics using multi-temporal data from terrestrial laser scanning (Tatra Mts., Poland)

From 2011 to 2019 high-mountain talus slopes in the Tatra Mts. were observed using terrestrial laser scanning (TLS) measurements. The digital-elevation models (DEM-s) derived from these measurements permitted the quantification of mass wasting processes with an accuracy of a few centimetres, and the lichenometric measurements allowed the detection of past activity of the talus slopes. The analysis focused on the mechanism and local conditions of talus slope response to hydrometeorological impulses in the context of climate change. The results showed that changes in talus slopes are essentially effects of debris flows. Significant differences in spatiotemporal changes between two adjacent talus cones were found to be related to their catchment lithologies. The spatial extent of talus slope change during the period of TLS monitoring is confined to debris flows tracks, and debris flows do not affect the entire talus cones as was the case in the past. Quantitative analysis of slope surface changes demonstrates that their final effect is building up of the talus slope, even if the debris flows moved part of the debris sediments out. Variability in the volume of displaced debris ranges from several dozen to almost 17,000 m 3 . A single input of loose debris from a massive rockfall dominated the effectiveness of debris flows and demonstrated the significance of the cooperation of mass wasting processes in talus slope morphodynamics as well as confirming the importance of the availability of loose debris for debris flows. This input influences slope morphodynamics, at least during the 8 years of observations, even if heavy rainfall occurred.