[dumpdaschle]

The 1908 Tunguska explosion was supposedly caused by an asteroid only 60 meters in diameter. That event felled an estimated 60 million trees over 2,150 square kilometres but did not leave a crater. It is believed that the asteroid exploded at an altitude of about 8 kilometres.
source - http://en.wikipedia.org/wiki/Tunguska

[konaice]

True, and the death toll was nill as far as anyone can tell. One wonders if a 400 meter asteriod would break up or land intact.