FRANKENSTEIN’S RIVERS: HOW REMNANT GLACIOFLUVIAL FEATURES SHAPE UNUSUAL RIVER NETWORKS IN LOW-RELIEF POST-GLACIAL LANDSCAPES

In the Central Lowlands (CL) physiographic province of the USA, lobes of the Laurentide ice sheet were primarily depositional. Sediment filled existing valleys, which disrupted existing drainage and resulted in post-glacial surfaces without broadly connected fluvial systems. During glaciation, glacio-fluvial processes occurred under and in front of the ice sheet, with variable water and sediment fluxes derived from glacial processes and unrelated to modern basin boundaries. Some of these glaciofluvial channel fragments remain in the modern landscape, indicating that post-glacial fluvial processes haven't entirely overwritten the glacial legacy.

Previous work has shown that, despite initially limited fluvial connectivity, the post-glacial landscape can develop and expand drainage networks to drainage density values similar to those of nearby unglaciated regions (Meghani and Anders, in review). Estimated rates of network expansion are orders of magnitude faster than expansion rates predicted by channel-head incision; the mechanism of channel development commonly invoked in steeper landscapes. Instead, we have previously proposed that there are three styles of features on the landscape that allow for this rapid integration of the post-glacial landscape: channels that were active during glaciation and that convey water today; topographic remnants of pro-glacial environments that have been repurposed or incorporated into fluvial networks; and channels that have developed following glaciation.

In this study we extend our previous work on the Sangamon River Basin (SRB), where we identified major signatures of pro-glacial processes in the sub-basins of the SRB and quantified their contribution to the modern fluvial network. Here we present a conceptual model for fluvial development in the post-glacial landscape of the CL, supported by new data from the SRB.