GLACIATION THROUGH THE LENS OF STRATH TERRACES (Invited Presentation)

The geomorphic legacy of Pleistocene glaciation includes bedrock river terraces, which form as sediment supply and transport fluctuate and drive either planation and floodplain widening or incision and narrowing. Simple models of sediment and water fluxes associated with glacial cycles predict cyclic terrace formation that lags several thousand years behind the glacial stimuli. Natural systems, however, are subject to a variety of spatial and temporal heterogeneities that alter the rates and timing of water and sediment supply. Here, we compile previously dated and studied strath terraces from around the globe to examine differences in terrace timing in response to glacial stimuli. We find that, despite terrace formation being driven by the same climatic forcing, the timing of terrace planation and incision varies with no discernable global trend. Regional climate patterns control the fluvial response to the global forcing. In arid climates, abundant sediment supply keeps the channel in a widening mode, with periodic incision triggered by precipitation change. In contrast, temperate climates often are dominated by sediment transport and are more sensitive to changes in sediment supply to drive terrace planation. Basin lithology further controls the timing and rate of sediment production and bedrock erosion within a channel and can result in asynchronous terrace formation within the same mountain range. Due to this complexity, the impact of glaciation on river systems across the globe is highly variable. Understanding the natural variability in fluvial response to glaciation is important to correctly tune and apply numerical models of landscape evolution and channel change, as the timing, rate, and magnitude of sediment and water fluctuation is unique to each watershed.