The destiny of orogen-parallel streams in the Eastern Alps: the Salzach–Enns drainage system

Abstract

Abstract. The evolution of the drainage system in the Eastern Alps is inherently linked to different tectonic stages of the alpine orogeny. Crustal-scale faults imposed eastward-directed orogen-parallel flow on major rivers, whereas late orogenic surface uplift increased topographic gradients between the foreland and range and hence the vulnerability of such rivers to be captured. This leads to a situation in which major orogen-parallel alpine rivers such as the Salzach River and the Enns River are characterized by elongated east–west-oriented catchments south of the proposed capture points, whereby almost the entire drainage area is located west of the capture point. To determine the current stability of drainage divides and to predict the potential direction of divide migration, we analysed their geometry at catchment, headwater and hillslope scale covering timescales from millions of years to the millennial scale. We employ χ mapping for different base levels, generalized swath profiles across drainage divides and Gilbert metrics – a set of local topographic metrics quantifying the asymmetry of drainage divides at hillslope scale. Our results show that most drainage divides are asymmetric, with steeper channels west and flatter channels east of a common drainage divide. Interpreting these results, we propose that drainage divides migrate from west towards east so that the Inn catchment grows at the expense of the Salzach catchment and the Salzach catchment consumes the westernmost tributaries of the Mur and Enns catchments. Gilbert metrics across the Salzach–Enns and Salzach–Mur divides are consistent with inferred divide mobility. We attribute the absence of divide asymmetry at the Inn–Salzach divide to glacial landforms such as cirques and U-shaped valleys, which suggest that Pleistocene climate modulations are able to locally obscure the large-scale signal of drainage network reorganization. We suggest that the eastward-directed divide migration progressively leads to symmetric catchment geometries, whereby tributaries west and east of the capture point eventually contribute equally to the drainage area. To test this assumption, we have reconstructed the proposed drainage network geometries for different time slices. χ mapping of these reconstructed drainage networks indicates a progressive stability of the network topology in the Eastern Alps towards the present-day situation.

Mobility and Location of Drainage Divides Affected by Tilting Uplift in Sado Island, Japan

“…Because the assessment of divide mobility is more accurate if the results of 𝜒𝜒 parameters and Gilbert metrics accord with each other, the combination of the Gilbert metrics and 𝜒𝜒 has recently been increasingly used [13][14][34][35]. In the case of conflict between the results of the Gilbert metrics and 𝜒𝜒, it is possible to interpret that the Gilbert metrics indicate the current divide mobility influenced by recent situation, and 𝜒𝜒 indicates the divide migration on a long-time scale [13].…”

Geomorphic expression of the Lenglong Ling area, eastern Qilian Shan, and its coupling relationship with the deep structures

“…Driven by the erosion contrast, the divide would migrate towards the side with lower slope, lower relief, and higher channel head elevation (Gilbert, 1877). The latest study suggested that using χ metric, in concert with the Gilbert metrics, is ideal for interpreting the current migration of the drainage divide (Forte & Whipple, 2018;Trost, Robl, Hergarten, & Neubauer, 2020). In this study, we used χ-map, in concert with the Gilbert metrics, as suggested by previous simulation result (Forte & Whipple, 2018), to investigate the condition of the Lenglong Ling divide.…”

“…Hence, the elevation metrics can be extracted by the channel head elevations. Local relief was determined by the range of elevation in a circular window and the slope gradient is the average topographic gradient between the channel head and the highest point within the analysed window (Forte & Whipple, 2018;Trost et al, 2020). In this study, the main divide of the Lenglong Ling was divided into four segments (i.e., AB, BC, CD, and DE segments) for detailed analysis (Figure 4), as suggested by Forte and Whipple (2018).…”

Dynamic Divide Migration as a Response to Asymmetric Uplift: An Example from the Zhongtiao Shan, North China

“…The metrics were firstly posited as that if a divide is asymmetric, that would induce differential erosion across the divide; driven by the erosion contrast, the divide would migrate towards the side with lower slope, lower relief, and higher channel head elevation [1]. The latest study suggested that using χ metric, in concert with the Gilbert metrics, is ideal for interpreting the current migration of the drainage divide [14,57]. In addition, if χ disagrees with the Gilbert metrics, this likely suggests that the Gilbert metrics may indicate current divide behavior, and that χ is indicating potential future divide behavior when the differences in uplift rate are eliminated [14].…”

“…Hence, the elevation metrics can be extracted by the channel head elevations. Local relief was determined by the range of elevation in a circular window and the slope gradient is the average topographic gradient between the channel head and the highest point within the analyzed window [14,57]. In this study, the main divide of the Zhongtiao Shan was divided into six segments (i.e., the ab, bc, cd, de, ef, and fg segments) for detailed analysis, as suggested by Fort and Whipple [14].…”