FORMATION OF THE GREAT LAKES, PAGE 4

10/15/2022

At present, there are 192 known Impact Craters in the world today that are of sufficient size to be noticed. A common denominator amongst these massive energy exchanges is the size of the rebound cone that exists after the collision incident solidifies. As the large object comes in at speeds that can exceed 18 miles per second, the material at the first initial impact zone is pushed up on the earth and some is vaporized. A portion of the floor becomes an instantaneous liquefied mass, then rebounds back up into the collision zone and solidifies like a mountain at the bottom of the crater. The rebound cone’s size and shape is dictated by the earthen material, the impactor’s composition (whether it is rock or ice), the speed (energy) that is expended in the collision and the availability of a liquid present to rapidly cool the collision. A classic example of the difference would be the Manicouagan Reservoir of Southeastern Quebec in Canada. This 214-million-year-old structure is now a hydroelectric dam reservoir that became very distinct on satellite photos as the perimeter filled in with water once the construction was complete. A 720-square-mile circle sports a 40-mile diameter inner ring expanding out to a 60-mile diameter outer ring that is quite visible on Google Earth. It was theorized to have been created by an object 3 miles in diameter, hitting the earth head on at high speed and leaving a 1148′ depth with layers of infill and a central rebound mass. It hit a very hard surface, known as the Canadian Shield, and is visible today due to this fact. Another example with a different outcome is Barringer Crater near Winslow, Arizona. It is 3/4 of a mile in diameter, 560-feet deep with 690′-790′ of infill above the original crater floor. Its rim is 148′ above the surrounding plateau and its rebound cone is small. It is a simple impact while the Manicouagan incident is considered a complex impact structure that appears in large object collisions between solid bodies. 

Lac Manicouagan, Quebec. A confirmed meteorite impact hit. An example of an impact crater lake. The large island in the middle is the rebound cone.

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