Closer to 9 miles (15km). That's plenty (even though it doesn't sound like much), considering what kind of eruption this would be and how the fault lines lie.
if(condition)
doSomething()
And naturally the obvious thing do to was to add a debugging statement: if(condition)
logSomething()
doSomething()
And if I remember correctly all of a sudden the bug didn't exist anymore for the condition I was reviewing. Took me a while to figure out what was going on. Lesson learned: Just always use braces.