© National Oceanography Center & National Institute of Water and Atmospheric ResearchMacauley volcano
An international team of researchers from the UK and New Zealand has discovered a previously undocumented type of eruption in underwater volcanoes.Volcanic eruptions are commonly categorized as either explosive or effusive.
Inside volcanoes, gases are dissolved in the molten magma as a function of the very high pressures and chemistry of the magma. In the same way that gases dissolved in carbonated drinks bubble up when you take the lid off, when magma is erupted as lava, the pressure is relieved and the gases exsolve to form small gas bubbles or so-called 'vesicles.'
In explosive eruptions these vesicles expand so quickly they fragment the magma, violently ejecting lava, which cools and degasses to form solidified pumice that can be sufficiently light to float on water.
In air pumice is obviously associated with violent, explosive eruptions. Consequently underwater volcanoes flanked by highly vesicular pumice have, to date, also been interpreted as having erupted explosively.