Wednesday, August 22, 2007

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 (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. This natural-color image of the region was acquired by the Multi-angle Imaging Spectroradiometer’s (MISR’s) nadir (vertical-viewing) camera on June 1, 2001.

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.

From Wikipedia....

Manicouagan Reservoir (also Lake Manicouagan) is an annular lake in northern Quebec, Canada, the remnant of an impact crater (astrobleme) made approximately 212 million years ago, towards the end of the Triassic period. It is the fifth largest known impact crater on earth [1]. Recent research has shown that the impact melt within the crater has an age of 214 ± 1 Ma. As this is 12 ± 2 Ma before the end of the Triassic, it implies that it was not the cause of the Triassic-Jurassic extinction event. The island in the centre of the lake is known as René-Levasseur Island. Mount Babel is the central peak of the crater.

The crater was created by the impact of a 5 kilometres (3 miles) diameter asteroid which excavated a crater originally about 100 km (62 mi) wide although sediments and erosion have since reduced its diameter to about 72 km (45 mi).

The Manicouagan reservoir and René-Levasseur Island are sometimes called the "eye of Quebec."

The lake was enlarged by flooding from the massive Manicouagan or Manic (Manic 1, Manic 2...) series of hydroelectric projects undertaken by Hydro-Québec, the provincial electrical utility, during the 1960s. The complex of dams is also called the Manic-Outardes project because the rivers involved are the Manicouagan and the Outardes. The lake covers an area of 1,942 km². Its eastern shore is accessible via Quebec route 389.

The Manicouagan lake acts as a giant hydraulic battery for Hydro-Québec. In the peak period of the winter cold, the lake surface is usually lower since the turbines are run all the time at peak load to meet the massive electrical heating needs of the province. The surface of the lake also sees record low levels in the extreme periods of heat in New England during the summer, since in that period Hydro-Québec sells electrical energy to the joint New England grid and individual utilities in the United States.

In 2007, the Manicouagan lake was astronaut Marc Garneau's nomination for the CBC's Seven Wonders of Canada competition.



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