# The 2014 Effusive Eruption at Stromboli: New Insights from In Situ and Remote-Sensing Measurements
## 3 Results
The collapse scar observed on a photo taken from helicopter (Figure 2a) had an estimated size of \(\sim\) 40 m width, 30 m high and 20 m depth, with a total collapsed volume estimated in \(\sim\) 24,000 m\({}^{3}\). Effusive vents moved northward from the NEC-hornito towards the NEC1. Afterwards, the displacement towards the sensor (up to 236 mm h\({}^{-1}\)) shifted from the NEC-hornito towards the NEC-talus (Figure 5c). Between 01:29 and 01:32 of 7 August 2014 (Figure 5c), the GBInSAR detected the formation of a fracture upslope of the NEC-talus. At the same time, the GBInSAR recorded an inversion in the LOS displacement rate (movements directed away from the sensor) in the crater terrace area, coherent with the deflation of the shallow conduit (Figure 5d). Figure 3: Relevant geophysical time-series from May to August 2014. (**A**) Landslide index derived from seismic data; GBInSAR cumulative displacement data for (**B**) the crater terrace and (**C**) for the NEC-talus. (**D**) Volcanic tremor amplitude at station STR1. (**E**) Explosion-quake amplitudes at station STR1. (**F**) VLP polarization inclination at station STRA. Figure 4: **(a)** The external flank of the crater terrace after the onset of the 2014 flank eruption (photo taken by INGV personnel on 11 August 2014 from helicopter survey). Lava overflows emitted during the run-up phase (F1 to F3) and lava flow produced during and after the onset (F4A and F4B) are also reported. **(b)** Detail of the NEC-talus area highlighting the scar produced during the onset of the eruption (7 August 2014), the first lava flow after crater breaching (F4A, erupted from vent V1), the upper portion of the 2014 lava flow field (F4B), and the vent of the 2014 flank eruption (V2) (photo taken by UNIFI personnel on 8 October 2014 from field survey). It is interesting to note the internal stratification in the NEC-talus remnants (consisting of volcaniclastic levels) that are continuous in all the inner walls of the landslide scar. At 05:04 V1 opened at \(\sim\)650 m a.s.l. (Figure 4) and at 05:08 the NE flank of NEC1 started collapsing, as evidenced by the associated high-frequency seismic signal (Figure 7). At 05:01, the live cam detected a downslope curved fracture opened on the flank of the NEC cone, followed at 05:16 by the opening of the effusive vent V2 at \(\sim\)650 m a.s.l. (Table 1 and Figure 4). The onset of the increased landslide activity occurred at 05:08, and its amplitude reached a peak at \(\sim\)05:24, i.e., during the opening of V1 and V2 (Table 1 and Figure 7). With the shift of the active vent from V1 to V2, a lava flow started spreading along the Pianoro (Supplementary Materials) and the flank eruption started. We analyzed in detail 24 h of high-frequency seismic signals related to landslide activity along the SdF starting from 10:00 on 6 August 2014 (Figure 7B). Between 10:00 and 18:00 on 6 August 2014, the repeated lava overflows triggered a moderate landslide activity along SdF (Figure 7A). Before the opening of vent V1, at 04:01 on 6 August, we observed a progressive increase in the landslides, which dropped just after this event. However, the clear onset of the increased landslide activity  
Figure 5: GBInSAR interferograms formed using a pair of images recorded between (**a**) the 12:09 and 12:20 on 6 August 2014, evidencing the instability of the NEC-hornito; (**b**) the 13:59 and 14:10 on 6 August 2014, evidencing the instability of the NEC-talus; (**c**) the 01:29 and 01:40 on 7 August 2014, evidencing the concomitant instability of the NEC-talus and the deflation of the crater terrace, coherent with the sliding of the NEC-talus induced by the NE-ward magma migration from the crater terrace; (**d**) the 05:26 and 05:37 on 7 August 2014, characterized by loss in SAR coherence due to fast movement both in the crater area (sliding processes) and along the SdF (lava flow emplacement). Interferograms in (**a**–**c**) are affected by phase wrapping.