Manicouagan Reservoir lies within the remnant of an ancient eroded impact crater (astrobleme). The crater was formed following the impact of an asteroid with a diameter of , which excavated a crater originally about wide, although erosion and deposition of sediments have since reduced the visible diameter to about . It is the Earth's sixth-largest confirmed impact crater according to rim-to-rim diameter. Mount Babel is interpreted as the central peak of the crater, formed by post-impact uplift.