The processes and feedbacks that induce multi-scale interactions between local divide migration, drainage reversal, and escarpment evolution

Overview: Water divides play a critical role in controlling the form of landscapes and shaping their hydrologic and geomorphic functionality. The location of the divides, and as a consequence, the geometry of the basins, are transient features of the landscape that respond to changing gradients in environmental conditions (eg, climate, lithology, tectonics). The mobility of water divides is inherently related to the local hillslope and fluvial processes that control the adjacent relief, and, at the same time, divide mobility could significantly influence large-scale topographic, isostatic, and stratigraphic patterns. The large«scale impacts of divide migration that emerge from the interdependency between scales are exciting, yet, the processes and feedbacks by which local hillslope and fluvial regimes interact with basin—scale drainage reorganization dynamics, and with large scale topographic and isostatic changes remain generally unexplored. In particular, the dependence of these processes on spatial variations in climate, lithology, and topography has received relatively little attention. To address these knowledge gaps, we focus on the juxtaposition of two landforms: (a) toprgraphic escarpments that are characterized by extreme slope imbalance across a drainage divide that separates a highland from lowland, and (b) reversed drainages; an end—member of drainage reorganization where channels reverse their flow direction by 180°. Reversed drainages are common along topographic escarpments and uniquely preserve the topologic record of drainage reorganization, as well as deposits and abandoned surfaces that are associated with the pre—reversal conditions. This, together with the commonality of escarpments across different climatic and lithologic settings, present a unique, data-rich opportunity to explore how local changes in the lilthologic and hydmlogic conditions act as a tipping point that drives the system into a cascading response, where local divide migration causes basin-scale drainage reorganization that leads to large-scale topographic changes and isostatic adjustments. To explore the generality of the emerging processes and feedbacks on the one hand, and to investigate site and condition specific processes, on the other hand, we will compare and contrast the emerging landscape dynamics in both arid and humid field sites (in Israel and the USA, respectively) across diflerent lithologic and tectonic settings. We will apply a multifaceted research strategy, where field observations and topographic analyses inspire new hypotheses and aid in testing them, and landscape evolution models and laboratory analyses constrain the parameter space and the rates associated with different processes and conditions for divide migration and escarpment embayment. Our preliminary field work an topographic analysis already established potential mechanisms where local lithologic conditions facilitate divide migration that causes drainage reversals that lead to the embayment of escarpments.

Intellectual Merit: The idea that local processes of divide migration and fluvial reorganization may influence large scale topographic patterns is exciting and has gained much attention recently. However, the feedbacks that enable small scale surficial processes to manifest as large scale topographic and isostatic changes are often overlooked. This study is unique in that it proposes to explore the details of such local processes and the specific feedbacks through which they influence large scale patterns. Understanding such multifiscale interactions has been highlighted as a key challenge by the geomorphologic and tectonic communities in recent documents, panels, and reviews. A transformative contribution of this study is therefore in establishing scenarios where local conditions trigger a cascade of feedbacks that influence topographic and isostatic patterns at very large scales. Additional exceptional merits of the proposed research include (1) the first direct measurements of divide migration rates as a function of time that stems from the unique depositional record preserved in hyper-arid reversed valleys, and (2) the emergent of rich cliff dynamics capable of explaining the remarkable variability of rate and style of escarpment evolution worldwide.

Broader Impacts: This study includes an enhanced science education program to K6-K12 students in Pennsylvania and Colorado that incorporates schools with high attendance of underrepresented populations. To demonstrate concepts of landscape evolution this program will combine a new siltbox apparatus with natural examples. Outreach deliverables produced through Pitt's Outreach Program will also be shared online with teachers across the country. Finally, this research will support four Early Career Scientists in the USA and Israel, and provide students from both countries with a multicultural scientific experience that will likely trigger future international collaborations.