Catchment-Averaged Erosion Rates Reveal Signals of Divide Migration and Drainage Capture

Abstract

Divide migration and drainage capture contribute to drainage reorganization. The relative contributions of each are debated, as are the extent to which an observable signal of drainage reorganization may be preserved in quantifiable erosion rates. We numerically model divide migration and drainage capture, and monitor the effects on catchment-averaged erosion rates in the growing (area gaining) and shrinking (area losing) catchments. Divide migration produces a rapid increase in catchment-averaged erosion rates in the headwaters of the growing catchment. However, we find this catchment-averaged erosion rate signal is quickly obscured with increasing distance downstream in non-uniform uplift settings, limiting our ability to detect divide migration through catchment-averaged erosion rate measurements in non-uniform uplift settings. Drainage capture produces the strongest catchment-averaged erosion rate signal immediately adjacent to the point of capture. We find this signal persists in the landscape longest, and without depleting in magnitude, in the area upstream of the point of capture. The Sierra la Laguna mountain range (Mexico) displays substantial evidence of recent and ongoing drainage capture across the main drainage divide, including: beheaded catchments, windgaps, barbed drainages, $\chi$ profiles and across divide Gilbert Metrics. We use the Sierra la Laguna to test the detectability of drainage reorganization related catchment-averaged erosion rate signals in a natural setting. ${}^{10}Be$-derived catchment-averaged erosion rates are found to be twice as fast in the suspected growing catchment headwaters (0.17 $mmy{r}^{-1}$) relative to the shrinking catchment headwaters (0.09 $mmy{r}^{-1}$). Catchment-averaged erosion rates, with distance downstream, share similarities with our drainage capture modeling.