Replies

It's not unheard of for asteroids to explode in the atmosphere before hitting the earth. A good example was the mysterious explosion which leveled a forest in Siberia in 1908, with the power of a nuclear bomb. Some theorize that it was essentially a comet, and that the large icey mass vaporized when it hit the Earth's atmosphere, causing a powerful explosion.

http://www.psi.edu/projects/siberia/siberia.html

(excerpt... see website for entire article)

In Brief:
At 7:17 AM on the morning of June 30, 1908, a mysterious explosion occurred in the skies over Siberia. It was caused by the impact and breakup of a large meteorite, at an altitude roughly six kilometers in the atmosphere. Realistic pictures of the event are unavailable. However, Russian scientists collected eyewitness accounts of the event. I believe that we now know enough about large impacts to "decode" the subjective descriptions of the witnesses and create realistic views of this historic asteroid impact as seen from different distances.

What do we know about the explosion?
You can get a sense of the magnitude of this event by comparing observations made at different distances. Seismic vibrations were recorded by sensitive instruments as much as 1000 km (600 mi) away. At 500 km (300 mi), observers reported "deafening bangs" and a fiery cloud on the horizon. About 170 km (110 mi) from the explosion, the object was seen in the cloudless, daytime sky as a brilliant, sunlike fireball; thunderous noises were heard. At distances around 60 km, people were thrown to the ground or even knocked unconscious; windows were broken and crockery knocked off shelves. Probably the closest observers were some reindeer herders asleep in their tents in several camps about 30 km (20 mi) from the site. They were blown into the air and knocked unconscious; one man was blown into a tree and later died. "Everything around was shrouded in smoke and fog from the burning fallen trees."