Groundwater storage variations in volcanic island aquifers using passive hydrogeophysical data: A feasibility study in Tenerife

Groundwater in volcanic islands is usually one of the main sources of freshwater, and it is essential for sustainable development. In Tenerife Island, groundwater extraction occurs mainly by drilling horizontal water tunnels or “galleries”, as well as coastal wells on coastal aquifers systems. Since around 1900, but especially since the 60’s decade, hundreds of galleries and wells have been drilled, mainly for agriculture, industrial and freshwater supply. This has resulted in a sustained extraction of groundwater larger than the natural recharge, leading to a general groundwater table decline (locally up to 200+ m of drawdown). Since 2000, satellite radar interferometry (InSAR) applied to measure surface deformation has located several subsidence bowls in Tenerife. The localized surface deformation patterns have been correlated with water table changes and hence aquifer compaction. 

To investigate the effect of compaction processes on our ability to track groundwater storage variations of volcanic aquifers, we have set up a spatially dense passive hydro-geophysical monitoring network composed of geodetic and seismological instruments. The network has been running since summer 2023 and also enhances satellite radar interferometry estimates of ground deformation associated with the aquifer compaction processes. Here, we present preliminary results of the hydrogeophysical network after its first 9 months of operation (almost one hydrological year, July 2023-April 2024). As a first step towards understanding the dynamics of groundwater in this setting, we correlate the simultaneous observations of land subsidence rates and ambient seismic wavefield changes with respect to environmental variables (e.g., air temperature and proxy for soil moisture and soil temperature measurements as a function of depth). This experimental study will allow us to get close to improving the effectiveness of water management policies in aquifers in volcanic islands. 

Acknowledgements: We thank Spanish Agencia Estatal de Investigación projects PID2019-104571RA-I00 (COMPACT) funded by MCIN/AEI/10.13039/501100011033, and Proyecto PID2022-139159NB-I00 (Volca-Motion) funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”. Thanks to the Teide National Park for the granted scientific permission to operate the geophysical network.