Quantitative assessment of the rockwall-talus slope system morphodynamics using TLS monitoring data (Tatra Mts., Poland).

The system rockwall-talus slopes is very common in the high-mountain. It develops mostly due to rapid mass movements, like rockfalls and debris flows. The quantitative data about changes of slopes and sediment transfer within the system enable to get to know complexity and controls of its morphodynamics. Using data from multi-annual temporal  monitoring by terrestrial laser scanning (TLS) survey of the rockwall-talus slope systems we examine their functioning in context of cooperation of rapid mass movements. The attention is paid to showing the different pattern of sediment transfer through the system and its controls.

The study were made in the Tatra Mts. The two adjacent rockwalls and talus slopes systems at the head of the Rybi Potok valley was monitored using terrestrial laser scanning TLS during last decade (2011-2021). They extend between ~1400 and 2500 m a.s.l. Their morphometric parameters are similar, but there is small hanging glacial cirque in one of them. The data was supplemented by meteorological data from the stations located in the bottom of the cirque and at the base of talus slopes.

The rockfall events occurred on the rockwall in each of the systems, which provided few thousands or dozen thousands of loose sediments to talus slopes. It was found that rockfalls occurred in effect of coupling geological and thermal conditions of rocks, not as result of permafrost degradation. The sediment transfer mechanism differs between the systems. The material transported by rockfalls was mostly deposited at the bottom of glacial cirque, while at adjacent system was transported to the apex of talus slope. Therefore activity of two adjacent talus slopes varies. The results showed that changes in talus slopes are essentially effects of debris flows. Their final effect is building up of the talus slope, even if the debris flows moved part of the debris sediments out. The studies reveal and confirm the importance of interplay between different extreme morphogenetic processes and show the complexity of talus slope transformation. A single input of loose debris from a massive rockfall dominated the effectiveness of debris flows. The studies also demonstrated differentiation of spatiotemporal pattern of sediment transfer trough rockwall-talus slope system. Moreover, relations between rapid mass movements and extreme rainfall and temperature as a result of climate change were found.