# The 2014 Effusive Eruption at Stromboli: New Insights from In Situ and Remote-Sensing Measurements
## 4 Discussion
Then, the location of effusive vents displayed a clockwise rotation along the rim of the crater terrace, from the NEC-hornito towards NEC2 and NEC1 (Figure 2), and finally magma migrated towards the NEC-talus, inducing fracture opening and landslides occurrence. This process suggested a gradual pressurization and/or expansion of the feeder dike along a SW-NE direction, which is also the main tectonic trend of the island [49; 50]. Lava started to outflow from a first vent (V1; Figure 10c) before the NEC-talus collapse and shifted at vent V2 simultaneously with the beginning of the NEC-talus landslide (Figure 10d). There could be different explanations for this vent shift:  
1. a structural barrier generated by the presence of a buried structure [51; 52] or different stratified material (Figure 2b), which in turn has caused the magma-filled fracture to re-orientate [53; 54];
2. magma to flow from V1 at V2 in response to the tensile stress occurring in the talus produced by the downwards displacement observed by GBInSAR. It is important to emphasize that this shift has prevented the dike from intruding within the SdF, as happened in the early stages of past eruptions (e.g., the 2007 eruption) [8]. Instead during the first days of the 2002-03 flank eruption, the intrusion of magma propagating laterally from the conduit towards a lower altitude was considered the cause that destabilized the SdF slope, with the triggering of tsunamigenic landslides on 30 December 2002 [22; 23; 24; 25]. The flank eruption onset produced the drainage of a superficial magma reservoir [5; 49], inducing ground deflation [55], a deepening of the VLP seismic source [5], and the cessation of summit explosive activity [5]. The volume of the drained magma can have critical implications on the eruption style and on its transition from effusive to explosive [56]. A previous author [4] calculated a total bulk volume of 7.4 \(\times\) 10\({}^{6}\) m\({}^{3}\) using data derived by the new satellite Technology Experiment Carrier-1 (TET-1) by the German Aerospace Center (DLR), whereas others [5] evaluated a total bulk volume of 5.5 \(\times\) 10\({}^{6}\) m\({}^{3}\) by thermal images from satellites using the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on-board the Terra and Aqua satellites. This last value was also confirmed by [57]. In MODIS approach, the error is usually estimated at 50% [58]. To improve the volume estimation, we calculated the topographic change by comparing the 2012 and 2017 DEMs. This approach considers the volume variations due to erosion and accumulation occurred between the two acquisitions, therefore also the topographic changes occurred before or after the eruption and the volume of the lava flow emplaced below sea level during the first days of the eruption. However, in this area there was no evidence of significant erosive phenomena [7], and moreover the evidence of large accumulation (i.e., more than 1-2 \(\times\) 10\({}^{6}\) m\({}^{3}\)) of lava or a debris flow under the sea is still missing [28]. We estimated that during the 2014 flank eruption, a volume of 3.07 \(\pm\) 0.37 \(\times\) 10\({}^{6}\) m\({}^{3}\) of lava was emplaced on the steep Sdf slope, i.e., most of the volume emplaced in the subaerial part of the volcano. This value is close to the previous estimations of 5.5 \(\times\) 10\({}^{6}\) m\({}^{3}\)[5; 57], which however comprises also the minor portion emplaced below sea level. Some authors [57] proposed that the critical factor for triggering the most violent explosive events (paroxysms, [59; 60; 61]) is the decompression rate, suggesting that rates \(>\)10 Pa s\({}^{-1}\) can potentially favor the ascent of gas-rich magma batches responsible for the paroxysmal explosions that occurred at Stromboli during the 2002-03 and 2007 flank eruptions.