The Manicouagan impact structure is one of the largest impact craters currently known on the surface of Earth. This shuttle oblique view looking south shows the prominent 70-kilometer-diameter, ice-covered annular lake that fills a ring where impact-brecciated rock has been eroded by glaciation. The lake surrounds the more erosion-resistant melt sheet created by impact into metamorphic and igneous rock types. Shock-metamorphic effects are abundant in the target rocks of the crater floor. Although the original rim has been removed, the distribution of shock-metamorphic effects and morphological comparisons with other impact structures indicate an original rim diameter of approximately 100 kilometers.
Space shuttle image STS51B-43-060.)