Narrower Paleo?Canyons Downsize Megafloods

Catastrophic drainage of glacial Lake Missoula through the Columbia River Gorge, USA, produced some largest floods ever known. However, erosion gorge during flooding has not been quantified, hindering discharge reconstructions and our understanding landscape change by megafloods. Using a neural network field observations, we reconstructed topography found ?7.4 km3 rock was eroded from walls. Accounting for narrower canyon matching flood high-water marks resulted in peak-flood 6x106 m3 s-1 to 7x106 s-1, which are 30–40% lower than prior estimates based on present-day topography. Sediment transport modeling indicated that more frequent intermediate-sized transported most rock. Thus, similar alluvial rivers, magnitude-frequency tradeoffs may also govern formation repeated