“Is there a 1-2 sentence explanation for why disaster would cause the currency to rise?”
I have to confess this mystifies me as well. Quite frankly it makes no sense at all to me, especially in light of the fact that the Bank of Japan just printed the equivalent of two billion U.S. to try and prop up the Japanese stock market, and presumably will keep printing as much as necessary to prevent its collapse until Japanese money is worth less than the paper it’s printed on.
A lot of the Japanese debt (bonds) is owned by the Japanese people proper. Not a lot of foreign held.
It could be that they (nationals and companies) decided to hold everything they could in cash as a safety measure or as a reserve to help with the tragedy, which means no one was selling yen....so it was a lack of supply driven rise and not a demand driven one.
Only thing so far I can think of that would make sense and it ties with the very conservative nature of the culture.