Not sure I understand your question, but the ash cloud will all eventually fall to earth. Don’t forget the sulfur and other aerosols which coming out by the cubic kilometer also.
IIRC,
past great eruptions have resulted in so much ash in the air that essentially, sunlight struck the surface of the earth enough less that days were shorter, nights longer
Isn’t that true?
that would fit the first part of the Scripture.
If the ash also shielded to some degree from the destructiveness of some types of rays . . . from extreme solar flares or some such . . . that might refer to the last part of that Scripture . . .
‘else no flesh would be saved.’
Vot you tink SunkenCiv?