Abstract
The topography of the eastern Southern Alps (ESA) reflects indenter tectonics causing crustal shortening, surface uplift, and erosional response. Fluvial drainages were perturbed by Pleistocene glaciations that locally excavated alpine valleys. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA‐EA drainage divide have not been identified. We demonstrate the expected topographic effects of each mechanism in a one‐dimensional model and compare them with observed channel metrics. We find that the normalized steepness index increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and amplitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease toward the east. Changes in slope of χ‐transformed channel profiles coincide spatially with the Valsugana‐Fella fault linking crustal stacking and uplift induced by indenter tectonics with topographic evolution. Gradients in χ across the ESA‐EA drainage divide imply an ongoing, north directed shift of the Danube‐ESA watershed that is most likely driven by a base level rise in the northern Molasse basin. We conclude that the regional uplift pattern controls the geometry of ESA‐EA channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration.
Highlights
Crustal deformation, climatic regime, and base level changes in the far field control the overall architecture of alpine drainage systems including the course of rivers, channel gradients, and the position of drainage divides [Miller and Slingerland, 2006; Willett et al, 2006; Stüwe et al, 2008; Bonnet, 2009; Champagnac et al, 2012; Willett et al, 2014; Yang et al, 2015]
We conclude that the regional uplift pattern controls the geometry of eastern Southern Alps (ESA)-Eastern Alps (EA) channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration
In order to disentangle various processes that drive ESA-EA landscape evolution by geomorphic properties, we demonstrate the impact of lithology, uplift rate, base level change, and glacial erosion on a simplified one-dimensional orogen
Summary
Climatic regime, and base level changes in the far field control the overall architecture of alpine drainage systems including the course of rivers, channel gradients, and the position of drainage divides [Miller and Slingerland, 2006; Willett et al, 2006; Stüwe et al, 2008; Bonnet, 2009; Champagnac et al, 2012; Willett et al, 2014; Yang et al, 2015]. Modeling studies imply that progressive shortening and deformation displace streams horizontally and vertically, deform drainage basins [e.g., Hallet and Molnar, 2001], impose flow directions upon large rivers by the activation of crustal scale strike-slip faults (e.g., orogen-parallel valleys), and distort the orogen-wide drainage network [Robl et al, 2008a, 2008b] Drainages respond to such perturbations via adjustment of watersheds by divide migration and river piracy events [Stüwe et al, 2008; Castelltort et al, 2012; Willett et al, 2014; Goren et al, 2015; Yang et al, 2015] and via adaption of channel gradients until they are in line with uplift rate and discharge of the river. Most mountain ranges are characterized by a transient topographic state featuring numerous mobile knickpoints and paleo-surfaces [e.g., Schlunegger and Schneider, 2005; Norton et al, 2008; Hergarten et al, 2010; Norton et al, 2010]
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