[mikey_hates_everything]

But it’s an underwater volcano. How does anything get to the stratosphere once it breaches the ocean surface unless it’s already lighter than air?

[palmer]

Sometimes a very strong storm can pop some water vapor through the tropopause (14 km in the tropics). That's about a 1% event and only 14 km. The volcanic explosion sent water vapor up about 40 km. That's never going to happen with water vapor from weather

How does anything get to the stratosphere once it breaches the ocean surface unless it’s already lighter than air?

By the time water vapor reaches tropopause it has cooled to about -50 or -60 and it's heavier again. Only the strongest convection can force it above and only a little bit above.