This computer-generated image by Sandia National Laboratories' scientists ...

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This computer-generated image by Sandia National Laboratories' scientists shows the impact of a 1-km comet (or asteroid) hitting in the open ocean. The comet and 300 to 500 cubic kilometers of ocean water would be vaporized nearly instantaneously by the tremendous energy of the impact. The impact energy of about 300 gigatons of TNT would be equivalent to about 10 times the explosive power of all the nuclear weapons in existence in the 1960s at the height of the Cold War. Download 150dpi JPEG image, 'comehit1.jpg', 384K

http://www.sandia.gov/media/comethit.htm

http://www.permanent.com/a-impact.htm