Why is the dollar dropping against the Japanese Yen?

One question we should be asking is why is the dollar dropping against the Japanese Yen since the earthquake, tsuanami and nuclear reactor issues.

Could it be that the dollar is on it's way to a bigger meldown than any nuclear reactor in Japan?

Maybe the Japanese are dropping the dollar, like a hot potato. After all do they not own a large share of  the U.S. Debt?