Tribulations always accompanied clouds for some reason, even when there was no lightning. For example, the Fire tribulation too took place underneath the black clouds of tribulation. Naturally, the Primordial tribulation also came from the clouds, unleashing an aura so powerful that the aura alone would be enough to kill Earth Immortals.
The fact that Lex, in spite of his tremendous growth, could not swim up due to the pressure from the clouds was a testament to the scale of the power they contained.
