Example; Pinatubo was a VEI 6, St Helens a 5.
So if you take St Helens and stand as ground zero-Pinatubo being a 6 was at ten feet. A 7 would be 100 feet, and an 8 would be 1000 feet. Krakatoa was a 7..If I remember right.
My bet is that this one will be at about a 5 because of it being largely under water.
They’ll determine it soon.
BTW, one of the biggest killers in recent history was one in Iceland-abt a VEI 4 which went on and on and pumped massive amounts of gas into the air.
The Geologyhub channel on Youtube said it is probably VEI 4.