What would be the safest place in the world to live if Yellowstone explodes?
If the Yellowstone caldera went super-active, no place on Earth would be ideally habitable given a short amount of time. A VERY large portion of the United States would be under extreme duress, but the rest of the world would eventually be blanketed with a very thick layer of ash. Granted, this would not be permanent, but the world would be at an effective stand-still for some number of weeks at a minimum. Here is the USGS take on the Yellowstone area, including some nice maps of historic eruptions: http://pubs.usgs.gov/fs/2005/3024/ To answer your question, it would be safe to assume that the areas depicted in pink in this image: http://pubs.usgs.gov/fs/2005/3024/images/fs2005-3024_fig_12.jpg …are not favorable for the extreme condition you reference. A general rule of a couple of hundred miles would also be a relatively useful guideline. No one can really say as this event would most likely be catastrophic and very difficult to model / predict.