Floodplain slope organizes chute and neck meander cutoffs across rivers in the Amazon basin

Channel cutoff is a fundamental mechanism by which meandering rivers of the Amazon reshape their courses, yet it remains unclear how their frequency and type vary across the river basin. Using satellite images from 1984 to 2021, we identified 1132 cutoffs across all single-threaded channels wider than 90 m. We find that cutoff types are unevenly distributed across the basin: Neck cutoffs (n = 594) dominate low-slope floodplains, while chute cutoffs (n = 456) are more common in steeper regions. Bimodal distributions of cutoff geometries indicate fundamentally different processes associated with neck and chute cutoffs. Results show that floodplain slope is a first-order control on cutoff type across the river basin, while water discharge and landcover act as secondary controls. The planform geometry of chute cutoffs is more scale-free than necks. This basin-wide perspective illustrates how cutoff type changes systematically across the Amazon, suggesting that floodplain properties control lentic habitat availability.