http://www.lpl.arizona.edu/impacteffects/ This site lets you play with some variables involving the impact of any size asteroid or comet hitting the earth. Some of the variables you get to enter are; size of asteroid, density of asteroid, angle of impact, composition of asteroid, and your distance from the impact. Once you enter these variables, the calculator gives a really detailed on how it will effect the area you put in, and basically the earth. REALLY COOL! One I put in was a 5.3 mile crater hitting South Carolina, about 2,000 miles away from me, here are just some of the things it gave back: