Integrating puffing and explosions in a general scheme for Strombolian-style activity

Strombolian eruptions are among the most common subaerial styles of explosive volcanism
worldwide. Distinctive features of each volcano lead to a correspondingly wide range of variations of
magnitude and erupted products, but most papers focus on a single type of event at a single volcano. Here, in
order to emphasize the common features underlying this diversity of styles, we scrutinize a database from 35
different erupting vents, including 21 thermal infrared videos from Stromboli (Italy), Etna (Italy), Yasur
(Vanuatu), and Batu Tara (Indonesia), from puffing, through rapid explosions to normal explosions, with
variable ejection parameters and relative abundance of gas, ash, and bombs. Using field observations and
high-speed thermal infrared videos processed by a new algorithm, we identify the distinguishing
characteristics of each type of activity and how they may relate and interact. In particular, we record that
ash-poor normal explosions may be preceded and followed by the onset or the increase of the puffing
activity, while ash-rich explosions are emergent, i.e., with inflation of the free surface followed directly by
emission of increasingly large gas pockets. Overall, we see that all Strombolian activities form a continuum
arising from a common mechanism and are modulated by the combination of two well-established
controls: (1) the length of the bursting gas pocket with respect to the vent diameter and (2) the presence
and thickness of a high-viscosity layer in the uppermost part of the volcanic conduit.