5.16 Polygenetic Landscapes

Earth's surface is continuously evolving and is the result of the complex interactions between Earth's internal (endogenetic) and external (exogenetic) processes. Endogenetic and exogenetic interactions result in landforms and landscapes that are the product of numerous different processes, and thus are ‘polygenetic’ in origin. Recent tectonic–geomorphic studies have led to the realization that complex links, interactions, and feedback exist among tectonics, climate, and landscape development. Key issues in the evolution of polygenetic landscapes included examining the role of tectonics and isostatic uplift, the nature of exhumation rates, climate control and erosion distribution, glaciers and relief production, focused erosion and spatial coincidence, geomorphometry and erosion modeling, and equilibrium concepts such as topographic steady state. Notably, the new models based on these complex relationships include: the glacial buzzsaw model whereby topography is limited by glaciation; the tectonic aneurysm model in which localized uplift at syntaxes is caused by enhanced fluvial and glacial erosion that, in turn, weaken the lithosphere and enhance bedrock uplift; and glacial damming leading to differential erosion and uplift. In addition to natural factors, human influences are now contributing to polygenetic landscapes and pose greater challenges for predicting the nature of future geomorphic change.