First 10 Megaton Hydrogen Bomb Test?

Question

In the video footage of the 1st 10 megaton hydrogen bomb test called IVY-MIKE at detonation the mushroom cloud does not appear for about 30 or 40 seconds after the blast.
exactly after the initial blast and before the mushroom cloud there appears to be a red transparent dome above the blast area.
what causes this tranparent bubble like dome before the explosion that creates the mushroom cloud?

Answer 1

The light and heat shock wave travels faster than the dust, which is the cloud. What you are seeing is dust particles in the air being heated red hot but the radaint heat wave