The notion that fluvial bedrock incision in response to tectonic uplift controls hillslope development has dominated recent models of mountain range evolution. It is an appealing concept that aims to integrate geomorphic hillslope–channel coupling, climate, and tectonic fluxes over a range of timescales. Yet the concept is partly at odds with the recognition that landsliding as a frequent erosional process in many active mountain belts occurs not exclusively in response to fluvial slope undercutting. Earthquakes, rainstorms, and exceeded internal stress thresholds cause and trigger large relief-lowering bedrock landslides not influenced by river processes. Moreover, these rock-slope failures mobilise sufficient material to block drainage networks, cause significant valley-floor aggradation, decrease in local relief, and stepped river profiles.
Such landslide-driven disturbances are mostly effective on 100–104 yr timescales and do not necessarily conflict with those of mountain range evolution (i.e. 106 yr; Fig. 13). However, they clearly demonstrate the potential for a more dynamic equilibrium in fluvial process rates and landforms. Hence, care should be taken when analysing the present topography, landforms, and process regimes in order to infer long-term rates of uplift and erosion. Quite conversely, such medium-term disequilibrium effects fill in nicely between short-term process studies and long-term models of mountain belt evolution on < 101 and > 105 yr timescales, respectively.