## 3 Results  
### Eruptive Activity between 28 March and 1 April 2020  
The eruptive activity taking place at Stromboli between 28 March and 1 April 2020 was studied using the images recorded both by satellites and by the INGV-OE monitoring cameras network. On 30 March and for the first half of the day on 1 April, poor weather conditions limited the visibility of the crater area. The explosive activity at the summit vents was rather intense on 28 March, with 20-25 explosions/h obtained from both cameras SPCT (West flank) and SCT (East flank of the SdF, Figures 1 and 3a). The eruptive activity took place at the NEC, featuring very intense explosions generating a spherical shape of incandescent spatters, which spread more laterally than vertically and all along the crater rim, fell on the NE outer flank and rolled down the SdF slope. This relationship between magma depth and column shape has been established previously [85], thus this shape of the explosions suggested that the level of magma within the vent was very shallow--estimated in a few tens of meters. Meanwhile, the explosions produced by the SWC were essentially of hot gas and ash with collimated jets extending more vertically than laterally, thus indicating that the level of magma within this vent was rather deep--estimated in a few hundred of meters [85]. At 15:38 the first landslide of hot debris coming from the NE rim of the NEC was observed, and it was followed by a powerful explosion. A similar landslide--the second reported on that day - occurred at 15:42, and it was apparently caused by the instability of the hot debris accumulated by the explosions on the steep slope of the NEC outer crater  
Figure 2: Examples of seismograms and spectrograms of seismic signals recorded at Stromboli in the studied period. Recording start times are reported at the bottom of each plot. The duration of the plots is one minute. (**a**) seismic signal and spectrogram produced by strombolian explosion; (**b**) seismic signal and spectrogram produced by volcanic tremor; (**c**) seismicity and spectrogram resulting from loose landslides; (**d**) seismic signal and spectrogram generated by blocks rolling down the Sciara del Fuoco slope; (**e**) seismic signal and spectrogram caused by pyroclastic density currents; (**f**) seismic trace and spectrogram recorded during the emplacement of lava flows. flank. Between 16:09 and 17:00 a series of small landslides from the NEC crater rim began, whose frequency increased in time until it became almost continuous. At 17:02 a lava flow started overflowing from a vent located at the base of the NE crater rim, and both thermal cameras suddenly recorded a significant decrease of the total number of explosions/h, from the previous 20-25 to 5-15 explosions/h (Figure 3a). At 17:44, the crater outline, as observed from SQV, showed a v-shaped cut in the crater rim, located above the effusive vent, which was caused by a collapse. The area of the missing block, estimated from the images recorded by the SQV camera, was \(\sim\)110 m\({}^{2}\). When considering a thickness of \(\sim\)10 m for the missing block, the volume of the crater rim eroded by the landslides resulted in \(\sim\)1.1 \(\times\) 10\({}^{3}\) m\({}^{3}\). The erosion caused by the spreading of the lava flows on the North flank of the cone, forming a channel that was also widening by failures and erosion of the lateral margins, was \(\sim\)1000 m\({}^{2}\), estimated again by the images of the SQV camera. When considering a thickness of \(\sim\)5 m for the collapsed area, a total volume of \(\sim\)5.0 \(\times\) 10\({}^{3}\) m\({}^{3}\) can be estimated. At 18:00, several incandescent blocks detaching from the lava flow fronts reached the sea, where formed an apron. After 19:00, the lava flow gradually decreased its output rate, and so did the number of landslides along the SdF, that had been triggered by the failure of incandescent blocks detaching from the flow fronts (Figure 3b).