Coexisting Strombolian and Hawaiian activity during the 2018 fissure eruption of K??lauea-Implications for processes of weak explosions*

Mildly explosive eruptions-the most frequent manifestations of subaerial explosive volcanism on Earth-broadly group into two styles: Strombolian and Hawaiian. The former is characterized by sequences of intermittent discrete explosions, and the latter by sustained pyroclastic fountaining. Explosive activity during the 2018 fissure eruption of Ki over bar lauea volcano (Hawai`i) provided an exceptional opportunity to record a wide range of Strombolian and Hawaiian behavior. We used high-resolution videography and image processing to quantify the frequency, duration, and steadiness (as seen by fluctuation in maximum clast height) of Hawaiian fountains and Strombolian jets. Combining these data with the currently published understanding of two-phase flow (melt + bubbles), we propose that the diversity in eruptive styles is related to melt viscosity, changing mass flux, and the extent of mechanical coupling versus decoupling of the exsolving volatile phases from the host magma. In particular, we single out the effects of the contrasts in abundance of a sub-population of the largest (meter-scale) bubbles that emerge intermittently and independently through the magma in the vent. The coexistence of these styles-at vents often only meters apart-is a clear indication that the diversity in eruptive behavior is modulated at depths of probably no more than 100 m and perhaps as shallow as tens of meters.