Hawaiian volcanoes are considered low in explosivity. “Effusive rather than explosive.”
This article from geology dot com shows some relative sizes and Eyjafjallajökull was about the same size as Mt. St. Helens. There are far, far bigger eruptions than Vesuvius.
https://geology.com/stories/13/volcanic-explosivity-index/
The Hawaii volcanoes are basaltic and are not normally explosive. This one is having explosive events due to magma interacting with ground water and is producing steam-generated eruptions.
The ones that really blow their tops are andesitic in composition.