Does anyone with knowledge about volcanoes have context on how big this is? Clearly not small, but is this a once-in-a-decade or a once-in-a-lifetime size explosion? Are there any well-known eruptions to compare it to (e.g. Mount St. Helens)?
It's probably gonna depend on how long it keeps erupting. Volcanic eruptions are rated (VEI index) on volume of material ejected, but each level has 10x more material than the previous.
If this were a volcano on land... I'd guess we are at a 4 or so. As this is a volcano that just barely breached the surface and thus interacts with water alot... maybe a 3? Volcanoes like this create really violent explosions (like the ones heard yesterday), but that doesn't necessarily require more material.
As said though, it'll be hard to tell without knowing how long the eruption went on and seeing the state of the island.
After checking the link, it seems it is saying this event is a 1 in 1000 year event for this volcano, not for the world in general.
I guess it could be both, but they don't appear to be saying that.