# The 2014 Effusive Eruption at Stromboli: New Insights from In Situ and Remote-Sensing Measurements
## 4 Discussion
A critical aspect is that the paroxysmal explosions of both 5 April 2003 and 15 March 2007 occurred while effusive activity was still going on, and when the lava effusion rate (related to the magma decompression rate) was decreasing with respect to the initial phases of the eruptions. Moreover, the 2002-03 and 2014 flank eruptions were characterized by the same mean effusion  
Figure 10: Schematic sketches representing the onset of the 2014 flank eruption as reconstructed on the basis of the new data presented in this paper. (**a**) The run-up phase of the 2014 flank eruption was characterized by high magma level beneath the crater terrace, which peaked on 6 August 2014 morning, with the occurrence of a large overflow from the NEC-hornito, triggering its collapse. Then the activity migrated from the NEC-hornito towards the NEC1. (**b**) The onset of the eruption coincided with the lateral dike propagation from the crater terrace along a NE-SW direction, triggering the instability of the NEC-talus, as evidenced by the increase in displacement rate at NEC-talus (until the loss of coherence in the GBInSAR data, compare with Figure 5) and landslides number (Figure 7). (**c**) Then the shift in the effusive vent from V1 to V2 occurred, (**d**) closely related to the NEC-talus collapse. Magmatic and mass-wasting phenomena are represented in red and in black, respectively. rate [57] but, differently from the 2002-03, the 2014 eruption did not produce any paroxysmal during the effusive activity. A different approach to understand the transition from effusive to explosive style can be obtained by estimating the cumulated effusive volume. In fact, a previous author [56] proposed that the erupted volume during flank eruptions at Stromboli is very important for hazard estimation, because it is considered a key factor for the triggering of paroxysmal explosive activity. [PERSON] et al. [56] proposed that there is an erupted magma bulk volume limit of \(6.5\pm 1\times 10^{6}\) m\({}^{3}\). Once that this volume is poured out, for example by drainage due to the opening of a flank fissure, the decompression induced on the shallow storage can trigger paroxysmal activity, by bringing at shallow levels the gas-rich magma that is in the lower conduit [62; 63; 64]. [PERSON] et al. [56] point out that the rate of effusion, and consequently the decompression rate, is less crucial to trigger powerful explosive activity. This interesting aspect has also been observed trough laboratory experiments allowing direct observations of explosive expansion of a slowly decompressed magma analog [65]. The analog experiments highlighted that under these conditions an explosive eruption would only occur when sufficient magma was spilled from the conduit, in agreement with the considerations of [56]. The inferred volume of 2014 emitted lava (\(3.07\pm 0.37\times 10^{6}\) m\({}^{3}\)), even adding 1-2 \(\times\) 10\({}^{6}\) m\({}^{3}\) of underwater volume not measurable with our DEMs approach, is below the limit of \(6.5\pm 1\times 10^{6}\) m\({}^{3}\) suggested by [56] and, therefore, consistent with the absence of the paroxysmal explosion. This consideration also explains the different behavior of the 2014 eruption (with absence of paroxysmal activity), respect to the 2002-03 eruption (with paroxysmal explosion). In fact, although the two eruptions had the same mean effusion rate, the 2014 emitted volume did not reach the critical limit (\(6.5\times 10^{6}\) m\({}^{3}\)) that was instead overcome by the 2002-03 eruption.