North Korea May Have Detonated a 250 Kiloton Bomb

The explosion was so powerful it sank an 85 meter area of Mount Mantap, underneath which the tunnel was buried. Synthetic aperture radar imagery from the Airbus TerraSAR-X satellite shows that the mountain actually lost elevation after the earthquake.

http://www.popularmechanics.com/military/weapons/a28211/north-korea-may-have-detonated-a-250-kiloton-bomb/