The Clearwater Lakes occupy the near-circular depressions of two
astroblemes – eroded
impact craters. The eastern and western craters are and in diameter, respectively. Both craters were previously believed to have the same age, 290 ± 20 million years (
Permian period), promoting the long-held idea that they formed simultaneously. According to this doublet impact crater theory initially proposed by
Michael R. Dence and colleagues in 1965, the impactors may have been gravitationally bound as a
binary asteroid, a suggestion also made by
Thomas Wm. Hamilton in a 1978 letter to
Sky & Telescope magazine in support of the then-controversial theory that asteroids may possess moons). Clearwater East and Clearwater West are both
complex craters with distinct central peaks. These peaks are caused by the gravitational collapse of crater walls and subsequent rebound of the compressed crater floor. Lake water and sediments cover the central peak of Clearwater East, but bathymetric surveys of the lake floor and core drilling confirm the presence of a peak in its center.
Ordovician Repeated
40Ar/39Ar dating of
impact melt rocks from both impact craters suggests that
Clearwater East has an age of approximately 460–470 million years, corresponding to the
Middle Ordovician time period. Both Clearwater impact structures also carry different geophysical (
natural remanent magnetization) signatures and different geochemical fingerprints of the impacting
meteorite in the
impact melt of each crater. . ==Microclimate==