A volcanic eruption is measured in two constants--gas and viscosity. For clearance, low viscosity is like squirting water off a nozzle, whereas high viscosity is like squirting caramel off a nozzle, which takes more effort to do, which makes it more dangerous.
In geology, there are four different kinds of volcanic eruptions:
- Low Gas + Low Viscosity = A quiet lava flow.
- High Gas + Low Viscosity = A fire fountain eruption.
- Low Gas + High Viscosity = A dome-building eruption. (This sort of eruption doesn't reach critical right away.)
- High Gas + High Viscosity = A Ring of Fire explosion.
These sorts of eruption are impressive enough on land, but in the event of someone doing some serious worldbuilding, this question puts three of the four types underwater. Type #1 has long been confirmed to happen underwater, but the oceanic differences in temperature and pressure have produced a different result called "pillow lava".
Is it possible for eruption types numbers 2, 3 and 4 to occur underwater? If yes, then would the oceanic differences in temperature and pressure make them look and act differently from how they have acted above sea level?