this is from the marvel directory:
Black Bolt possesses various superhuman powers stemming from his ability to harness free-floating electrons. The speech center of Black Bolt’s brain contains an organic mechanism able to generate an as yet unknown type of particle which interacts with ambient electrons to create certain phenomena determined by mental control. The most devastating of the effects is Black Bolt’s quasi-sonic scream. Because his electron-harnessing ability is linked to the speech center of his brain, any attempt to use his vocal cords – from the merest whisper to a full scream – triggers an uncontrollable disturbance of the particle / electron interaction field. This result in a shock wave equivalent, at maximum force, to that caused by the detonation of a nuclear weapon. A whisper has generated sufficient force to rock a battleship, while a scream can reduce a mountain to rubble.