Why does Megaton exist? It is a crater, made by an undetonated bomb, which neither exploded, nor was crushed to the size of a soda can by impacting the earth at such speed as to create that hole in the ground. How people managed to survive long enough out there after being locked out of the Vault and were able to assemble a huge city from scraps of airplane that somehow appeared out there, mostly intact, after the Earth and everything on it was burnt to a crisp