The large annular
lake in this image represents the remnants of one of the largest impact
craters still preserved on the surface of the Earth. Lake Manicouagan
in northern Quebec, Canada, surrounds the central uplift of the impact
structure, which is about 70 kilometers in diameter and is composed of
impact-brecciated rock. Glaciation and other erosional processes have
reduced the extent of the crater, with the original diameter estimated
at about 100 kilometers. The impact that formed Manicouagan is thought
to have occurred about 212 million years ago, toward the end of the Triassic
period.
Photos courtesy
of NASA
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