It is well known that the volcanic gas is the main controlling factor during an eruption. It’s the gas that drives the magma from the deep to the shallower layers and then until the surface. It’s the gas ruling the style of the eruption, whether explosive or effusive. In summary the range of behaviours of the volcanoes is just controlled by the amount and type of gases involved.
Locals from Etna or Stromboli will testify how the gas is continuously released: every single day a plume of gas rises from the top craters and marks the sky with a white stripe.
Volcanologists monitor the volcanic gases, measuring the quantity and the various species (H2O, CO2, SO2, etc.). Well, the incredible amount of some tens of thousands of tons are released everyday from Etna, and even more during eruptions.
The video shows the “smoking” craters of Etna during a time span of 10 minutes in March 2019.
Aiuppa, A., Fiorani, L., Santoro, S., Parracino, S., D’Aleo, R., Liuzzo, M., … & Nuvoli, M. (2017). New advances in Dial-LiDAR-based remote sensing of the volcanic CO2 flux. Frontiers in Earth Science, 5, 15.
D’Aleo, R., Bitetto, M., Delle Donne, D., Coltelli, M., Coppola, D., McCormick Kilbride, B., … & Aiuppa, A. (2019). Understanding the SO2 Degassing Budget of Mt Etna’s Paroxysms: First Clues From the December 2015 Sequence. Frontiers in Earth Science.