Thinks... no thermals to keep it up, condensation of water due to much lower temperature = fallout.
Thermals
won't be keeping ash up... they'll be stirring it up maybe in the lower few thousand feet.
1/3 air mass goes up in thermals when they're popping, the other 2/3 comes down half as fast as the 1/3 that goes up - roughly!
If
all the air went up in thermals, we'd die
