Abstract— <p>Middle-Late Pleistocene giant ice-dammed paleolakes occupied in the Pleistocene Uimon (lake volume 450 km³), Kurai (229 km³), Chuya (838 km³), and Kan-Yabogan basins of Gorny Altai, southern Siberia. The lake volumes were estimated along the contours of wave-cut terraces, and Kurai and Chuya lakes taken together turned out to fit the 1056 km³ size of a temporary paleolake, which formed in the Biya-Barnaul segment of the Ob Valley due to flooding of the Fore-Altai plain by megafloods. However, no megaflood events were associated with breakthrough of rockfall-dammed lakes in the Chuya and Katun valleys or small ice-dammed lakes in Gorny Altai. Abrupt discharge of lakes through broken ice, landslide, or moraine dams could cause floods in the Chuya and Katun valleys about 18–14 ka ago, but their volumes and the effects of erosion, sediment transport, and terrain sculpturing were far inferior to those of the older glacial megafloods.</p>