I'm guessing you're using an ATI graphics card? If so this is an issue that's been there basically since the beginning and which SE doesnt seem to want to do anything about. There used to be a 150+ page long thread about it but it was moved to the resolved section (and no, nothing has really been resolved). There is a work around which i think involves disabling all the LOD features in your graphics settings, but ofcourse the game will look worse with objects only starting to look good when you're really close to them (oh and another side effect is armour models never using high detail, no idea why). So those are currently your options: random crashes or game looking crappy for no real reason.. until SE and AMD finally start cooperating on the issue.