Characterizing spatio-temporal changes in volcanic rock aquifer compaction using satellite-based geodetic measurements (GNSS and InSAR)

Volcanic reservoirs are usually the main source of freshwater on volcanic islands. On Tenerife Island, groundwater extraction occurs by drilling horizontal water tunnels. This has resulted in a sustained extraction due to the hundreds of water tunnels that have been drilled since around 1900 for agriculture, industry and freshwater supply. The extraction is exceeding the natural recharge, leading to groundwater table decline, locally up to 200+ m of down drop. Since 2000, satellite radar interferometry (InSAR) applied to measure surface deformation has located several subsidence bowls (e.g., Fernandez et al., GRL 2009). The localized surface deformation patterns have been correlated with water table changes and hence aquifer compaction. By overlapping InSAR data time series with Global Navigation Satellite Systems (GNSS) we hope to better understand the compaction processes around volcanic aquifers and explain the observed surface deformation.  This knowledge could help make decisions about water management policies.

To investigate the compaction processes affecting the volcanic rock aquifers of Tenerife, we utilize simultaneous geodetic observations using Global Navigation Satellite Systems time series (GNSS) and satellite radar interferometry over the period October 2014 to December 2021. The GNSS network is composed of 10 GNSS sites and it was processed by the Nevada Geodetic Laboratory (Blewitt et al., 2018; http://geodesy.unr.edu/NGLStationPages/gpsnetmap/GPSNetMap.html). The satellite radar interferometry time series were computed using Sentinel-1 ascending and descending orbits with ID tracks 060 and 096, respectively. Finally, we analyzed the spatio-temporal behaviour using statistical methods to identify distinct regions more or less affected by the underlying aquifer mechanical processes. 

Blewitt, G., W. C. Hammond, and C. Kreemer (2018), Harnessing the GPS data explosion for interdisciplinary science, Eos, 99,https://doi.org/10.1029/2018EO104623.

Fernandez, J., et al. (2009), Gravity-driven deformation of Tenerife measured by InSAR time series analysis, Geophys. Res. Lett., 36, L04306, doi:10.1029/2008GL036920.