## 6 Discussion and Conclusions  
The current monitoring network of Saba and St. Eustatius is in development. The goal is to enhance the monitoring capability in liaison with the volcanic threat. Future improvements include (i) the installation of a seismic station in the SE of St. Eustatius and the NW of Saba; (ii) two more GNSS stations on each island, with one station on each island co-located with the seismic equipment just mentioned if possible; (iii) a more durable temperature sensor which transmits data in real-time to  
Figure 14: The hot spring opposite Green Island showing the attachment of two tinytag plus 2 data loggers to the cliff face and the cable path towards the submerged spring. monitor the hot spring on Saba; and (iv) investigations to better understand the mass out-of-balance of the seismometers. The first scouting for potential sites to fulfill point (i) was done in early 2018, and two potential sites, one on each island, were identified. Neither of them has power nor communication facilities available; therefore, the installation will be more complex and will require solar panels and a battery as well as a way to transmit data to KNMI. More investigations are needed to successfully complete this task in an affordable way. Further expansion of the monitoring network, including observations with other techniques, remains possible. Campaign GPS/GNSS measurements would increase the deformation data coverage and when revisiting previously observed sites [35], changes through time could be evaluated. The Interferometric Synthetic Aperture Radar (InSAR) technique uses satellite images, covering the whole islands, to detect centimeter-scale surface deformation through time. Even though the technique is hampered by shadowing effects due to steep topography and by coherence loss in vegetated areas, the observations can be useful, as was shown by the example of the neighboring island of Montserrat [44]. InSAR observations may thus complement the existing measurements without requiring field visits or expensive equipment. Setting up a monitoring network requires time, effort, and finances and can be complicated in areas that are not in close proximity to the monitoring agency (KNMI, in this case). Continued support, financially and scientifically, as well as from the local government and populace, is required to sustain such a network. To enable the observation of changes in geophysical parameters and to ensure timely warning, a monitoring network needs to be operational even when volcanic activity remains at background levels. More specifically, it is crucial to establish a monitoring network before any activity takes place. Despite the fact that sustaining such a network in tropical conditions remains a challenge, it is the only way to ensure that potential future volcanic activity is detected in advance, benefiting the safety of the local populations. This work helps to prepare for future hazards, while, at the same time, it provides value added to space weather, earthquake, and tsunami studies/warnings. R.S. started the network set-up in 2006 with contributions from KNMI colleagues. Progression towards a volcano monitoring network was initiated by E.d.Z.-v.D. and carried out by E.d.Z.-v.D. and R.S. with support of technicians from KNMI. R.S. maintained the seismic network over the years and performed all seismic data analysis. E.d.Z.-v.D. designed the GNSS benchmarks with contributions from KNMI technicians and conducted the GNSS data analysis. E.d.Z.-v.D. and R.S. equally contributed to the writing of the manuscript. This research received no external funding. We are very grateful to [PERSON], and his colleagues from the Meteo Service St. Maarten, who always selflessly supported the build up of the seismic network since 2006 in many ways. Also the continuous help from [PERSON] and his colleagues from Satel, and from [PERSON] from Eitel, for more than 10 years, is very much appreciated and still is very important to make our monitoring network successful.