What happened in North Korea?

Im just curious, but not so long back the North Koreans had a major explosion near the border of China if i remember rightly.

IT was told to be some ground works for a damn, or station they were building.

Well we never heard any more of it. Interesting now especially since NK have come forward saying they have nuclear weapons.

And I remember from the reports being given about the mushroom cloud seen, that it must of been an enormous amount of TNT... a lil TOO much TNT if ya ask me.

Anyone hear any more on it ?