Switching between ordinary and non-ordinary activity at Stromboli volcano: insights from short- and long-term thermal trends recorded from space

Ordinary, moderately explosive activity at Stromboli is sporadically interrupted by larger effusive and explosive events that can trigger hazardous phenomena such as sector collapses, tsunamis, and ballistic fallout. We analyze 25 years of satellite infrared data to characterize the thermal pattern associated with these larger events, including: (1) effusive eruptions, (2) lava overflows, (3) major explosions, and (4) paroxysms. Increased heat flux precedes effusive eruptions and overflow sequences, and is interpreted to reflect the progressive rise of the magma column in the conduit accompanying the transition between Strombolian and effusive regimes. Conversely, major explosions are not preceded by any detectable thermal increase, although they statistically occur during periods of frequent overflows in which the Volcanic Radiative Power (VRP) is punctuated by higher values. Paroxysms (which occurred at the beginning, during and at the end of the effusive eruptions) do not show systematic thermal patterns in the preceding days, but in most cases are followed by a VRP increase. Major explosions and paroxysmal events contribute minimally to the long-term energy released by the volcano. Instead, the energy output is primarily governed by the recurrent transitions between Strombolian- and effusive-dominated regimes, sustaining a long-term, steady-state VRP of approximately 14.5 MW. Overall, only ~ 25% of the thermal energy is radiated during Strombolian activity, whereas overflows and effusions account for ~ 15% and ~ 60%, respectively. Results highlight that satellite thermal analysis is a useful tool for tracking changes of surface activity at open-vent basaltic volcanoes with frequent switching from ordinary low-energy activity to more energetic explosive or effusive eruptions.