## 5 Conclusions  
This paper analysed the lithosphere, atmosphere, and ionosphere, and their possible interactions before the La Palma Cumbre Vieja 19 September 2021 VEI = 3 volcano eruption. We identified a migration of the seismicity from the deepest sources at about 40 km to superficial seismicity, which follows a temporal order, strongly suggesting a magma migration from about October 2020 that gradually fills a probable deep magma reservoir identified by a gap of seismicity between 13 km and 20 km depth that could coincide with the one already identified by [PERSON] [89], which was completely filled in February 2021. In the 10 days before the eruption on 19 September 2021, the magma uplifted in the magmatic volcano chamber was located at less than 5 km depth, which can be seen as another seismicity gap already described by [PERSON] et al. [91]. We identified several atmospheric and ionospheric anomalies from CSES-01 and _Swarm_ satellites from 130 days to 90 days before the eruption, suggesting a bottom-up interaction between the two layers, even if other explanations are possible or the disturbances could be even independent. About two months before the eruption, electron density profiles depicted an anomalous electron density peak close to the volcano (confirmed by _TEC_ maps). At a similar time, minor seismicity was recorded. A final increase of carbon monoxide started about 1.5 months before the eruption suggesting CO as a strong proxy of the magma's uplifting, i.e., the explosion's preparation. In particular, CO mean value was always above the historical mean in the last month, and a final strong acceleration of seismicity in the last 10 days clearly preceded the event. At the same time, the _TEC_ also shows anomalies from 2 months before the eruption with synchronicity with the release of CO and the seismicity acceleration. This could suggest an interaction between the geo-layers even if it cannot demonstrate that the synchronicity was a cause-effect relationship, or that it occurred only by chance. This research not only confirmed previous investigations of pre-eruptive activity of La Palma volcano that investigated seismicity, CO\({}_{2}\) and helium, and land deformation  
Figure 30: Pointing vector of Swarm Bravo data acquired on 26 July 2021, track 6. The three components in the North, East, and Centre reference frame are represented in (**A–C**), respectively. A 3D reconstruction of the vector is provided in panel (**D**), together with the green star with the position of the “La Palma” volcano, and the dashed grey line is the ground projection of the satellite track. from radar satellites [89; 91], but it is also complementary in terms of other investigated parameters and new lithospheric activity discovered from this study helping to understand the complex possible mantle-lithosphere-atmosphere-ionosphere interactions. Future studies need to provide more substantial proof of such interactions between lithosphere atmosphere and ionosphere as in the present study; the interactions are proposed as our best interpretation of the results. Still, we cannot exclude other interpretations or sources of the identified anomalies. Such a study underlines how crucial global monitoring of geophysical hazards such as volcano and earthquakes is, with a wide network of sensors on the ground and satellites. Their integration not only permits better understanding of the nature of our planet, but also could potentially help in the future to predict dangerous events, contributing to saving human life and reducing economic losses.