[dumpdaschle]

It sounds as if asteroids less than 100 meters in diameter generally do not hit the ground. But, it would still cause massive local damage whether it hit the ground or not. I believe that nuclear warheads explode in the air for maximum affect. The Tunguska event area of destruction was within a circle radius of 25 kilometers.

This site has some interesting info - http://users.tpg.com.au/users/tps-seti/spacegd7.html
and there is information on this site about the tsunami effect caused by asteriods.

The web site mention above says that an impact from a 2km diameter stony asteroid is thought to be at the threshold of a global catastrophe and the "damage" would go well beyond the area of direct devastation. It has been estimated that one quarter of the world's population could die from starvation and other indirect effects due to a 2 km asteroid impact.

[konaice]

This site has some interesting info - http://users.tpg.com.au/users/tps-seti/spacegd7.html and there is information on this site about the tsunami effect caused by asteriods.

Yup, that pretty well agrees with what I learned on this subject. The 400meter object is far from a planet killer, and the better prediction of impact area (if it does in fact hit) the better chances we have of avoiding a high death toll, as I mentioned in my #111 above.