## 5 Conclusions
The main results of this study can be summarized, as follows:  
* before the analyzed phase, the explosive activity at the summit vents was reasonably intense (20-25 explosions/h), with a prevalence of explosions that produced coarse material in the NEC (i.e., shallow magma level in the conduit);
* the 28 March 2020 overflow was anticipated by some landslides that involved the material accumulated in the areas around the NEC (total eroded volume \(\sim\)5-6 \(\times\) 10\({}^{3}\) m\({}^{3}\)), even if these did not generate a substantial widening of the crater itself;
* the first overflow was accompanied by a decrease of the total number of explosions/h (from the previous 20-25 to 5-15 explosions/h);
* PDCs were also generated by the crumbling of the overflow front, they reached the sea and formed an apron on the coast;
* no ground deformation was recorded before nor after the 28 March event, meaning that the lava flow volume was small;
* after the first overflow, the number of landslides detected with the seismic network decreased, while the number of explosions increased again, suggesting a new upward movement of the magma level within the conduit;
* the onset of the new overflow phase occurred on 30 March together with a new sharp reduction in the number of explosions, a new increase in the number of landslides, which produced a significant variation in the morphology of the crater and which were associated with the accumulation of incandescent material along the coast line;
* the PDCs linked to the initial phase originated from the NEC area (total eroded volume \(\sim\)7.3 \(\times\) 10\({}^{3}\) m\({}^{3}\)), whereas, as the effusive phase progressed, the subsequent PDCs were generated directly by crumbling of lava flow front along the steep slope of the SdF;
* PDCs reached the sea with variable speed (between 12.9 and 40.3 ms\({}^{-1}\)), partly flowing on the water;
* the entry into the sea of these mass-flows is associated with a strong variation in seismic signals, with the disappearance of the typical signal associated with the landslides in Stromboli (high frequency; 4-15 Hz) and the appearance of another one characterized by a large amplitude and lower frequency (1-3 Hz);
* this change in the seismic signal could be due to the PDC entrance in the underwater environment, as well as to the resonance of the Stromboli conduit, which is located in the volcano edifice, at a small depth below the SdF;
* the lava overflows that were emplaced between 28 March and 1 April covered a total area of 94,500 \(\pm\) 3380 m\({}^{2}\);
* the volume of the deposits accumulated from October 2019 to April 2020 near the NE crater amounts to 34,600 \(\pm\) 9700 m\({}^{3}\), whereas the volume in the overflows area was of 144,400 \(\pm\) 79,000 m\({}^{3}\), for a total amount of 179,000 \(\pm\) 89,000 m\({}^{3}\). Thermal satellite data also allowed for constraining the DRE lava volume between 37 and 69 \(\times\) 10\({}^{3}\) m\({}^{3}\) emplaced from 30 March to 1 April 2020; integrating this result with those that were obtained from DEM difference, a lava volume of \(\sim\)80.5 \(\times\) 10\({}^{3}\) m\({}^{3}\) could have been emitted during 28 March-1 April. **Author Contributions:** Conceptualization, S.C., F.D.T., G.G., F.G. and G.M. ; methodology, S.C., F.D.T., G.G., A.C., F.G., G.M., and E.P. ; validation, S.C., F.D.T., G.G., F.G. and G.M. ; formal analysis, S.C., F.D.T., G.G., F.G., G.M., T.N., E.P., and A.C.; data curation, S.C., F.D.T., G.G., F.G., G.M., E.P., A.C., G.B., C.C. and V.C. ; writing--original draft preparation, S.C., F.D.T., G.G., F.G., G.M., A.C., and C.D.N. ; writing--review and editing, S.C., F.D.T., G.G., F.G. and G.M. ; visualization, S.C., F.D.T., G.G., F.G. and G.M. ; supervision, S.C., F.D.T., G.G., F.G. and G.M. ; project administration, S.C., T.N., G.G., F.G. and G.M. ; funding acquisition, N.C. and C.D.N. All authors have read and agreed to the published version of the manuscript.