One of the people on one of the maiing lists I’m on sent a message around with the following link:
It’s a YouTube video about what happens when a 500-km asteroid hits the Pacific Ocean. Hint: for ‘atmosphere’ think ‘silicate vapour’.
He adds, "Click on the ‘more’ link in the ‘About This Video’ box for an English translation of the Japanese narration (you’ll still get a pretty good picture even without the narrative). "
Some of the other videos referenced on the same page are rather interesting as well. There’s one about the formation of the moon.