Stream erosion in analogue models

Abstract

The presence of a strong interaction between tectonic deformation and surface processes is widely recognized. Still, the nature of this interaction is difficult to unravel and quantify. In the last decades, analogue landscape evolution models have been widely implemented and employed in different tectonic settings, to complement field campaign studies. Since the aim of these analogue models is to help the interpretation of data coming from natural prototypes, it is important to test how well empirical erosional laws built upon natural landscapes, explain analogue model behavior. We perform a series of experiments for a straight interpretation of the relationship between applied boundary conditions and analogue landscape evolution. The selected analogue material is composed of 40 wt.% of silica powder, 40 wt.% of glass microbeads, and 20 wt.% of PVC powder. The analogue material fills a rectangular box (30×35×5 cm3) placed over a reclined table. Over the box, a series of sprinklers generate a dense mist (i.e., rainfall) that triggers surface processes. The boundary conditions applied to the models are the imposed slope of the reclined table and the rainfall rate. We test three rainfall rates (9, 22, and 70 mm h-1) and three imposed slopes (10, 15, and 20°), analyzing how the combination of these boundary conditions results in different landscape metrics (e.g., basins length, basins width, drainage area, channel slope, erosional efficiency) and erosion rates. Results show that in models affected by high rainfall rates (70 mm h-1), the implemented analogue material is characterized almost no channelization, and erosion acts uniformly and diffusively over the models’ surface. Lower rainfall rates (9, 22 mm h-1) allow more discrete channelization instead. On the other hand, as expected, the imposed slope controls the amount of incision, so that the volumes of material removed by erosion increase moving from 10° to 20°. However, even if the maximum incision is generally controlled by the slope, the coupling with rainfall rate tunes the effectiveness of erosion. In this work we compare the imposed boundary conditions with the corresponding erosion rates, using geomorphic markers and landscape metrics to define if and how natural erosional laws apply to analogue landscape evolution models.