A 20-km asteroid has just been predicted to hit Earth and you want to know if a. You should run for it, b. You should call Bruce Willis, or c. You can rest easy because your part of the world won’t be affected. All you have to do is input the parameters of the asteroid on the recently updated “Impact Earth” website, and you’ll find out everything about what an impactor will do to Earth, including an estimate of the size of the crater, how far away you’ll need to be in order to avoid being affected by the impact (and if that is possible), tsunami wave height, and other details of the subsequent disaster. The fun part is, you can simulate the destruction of Earth multiple times, without hurting anyone.
The original Impact Earth website was created in 2002 for use by NASA and homeland security. The new version, built in a collaboration between Purdue University and Imperial College London, is more user-friendly for the general public, as well as providing more visual details of an impact. Besides being rather fun to play around with, the website is highly educational about what a various sized impacts would do Earth, depending on if it hit ground or water.