Stronger or longer: Discriminating between Hawaiian and Strombolian eruption styles

The weakest explosive volcanic eruptions globally, Strombolian explosions and Hawaiian fountaining, are also the most common. Yet, despite over a hundred years of observations, no classi cations have offered a convincing, quantitative way of demarcating these two styles. New observations show that the two styles are distinct in their eruptive time scale, with the duration of Hawaiian fountaining exceeding Strombolian explosions by ~300–10,000 s. This re ects the underlying process of whether shallow-exsolved gas remains trapped in the erupt- ing magma or is decoupled from it. We propose here a classi cation scheme based on the duration of events (brief explosions versus prolonged fountains) with a cutoff at 300 s that separates transient Strombolian explosions from sustained Hawaiian fountains.