Clouds around Manicouagan Reservoir
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Clouds around Manicouagan Reservoir

July 23, 2009
Clouds mimic the shape of the landscape in this image, captured by the MODIS on the Terra satellite on July 7, 2009. What is beneath the clouds is a lake called the Manicouagan Reservoir, located in Quebec, Canada. The lake is circular because it is actually the remnant of one of the largest impact craters still preserved on the surface of the Earth.

The lake actually surrounds the central uplift of the impact structure, which is about 70 kilometers in diameter and is composed of impact-brecciated (relativley large pieces of rock embedded in finer grained material) 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. Some scientists believe that this impact may have been responsible for a mass extinction associated with the loss of roughly 60% of all species. It has been proposed that the impact was created by an asteroid with a diameter of about 5 kilometers. The lake is bounded by erosion-resistant metamorphic and igneous rocks, and shock metamorphic effects are abundant in the target rocks of the crater floor. Today Lake Manicouagan serves as a reservoir and is one of Quebec's most important regions for Atlantic salmon fishing.

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