Microgravity Surveys for Volcano Monitoring in the Canary Islands

The primary objective of this study is to detect and analyse subsurface density variations that could indicate magmatic movements or other geological processes associated with volcanic activity in the Canary Islands. Microgravimetry is a geophysical technique that measures spatial and temporal variations in the Earth's gravitational field over its surface, allowing the detection of density changes within the crust. For this reason, it is a valuable technique in volcano monitoring, capable of detecting changes in a volcanic-hydrothermal system. This information is crucial for understanding the dynamics of volcanic systems and assessing potential volcanic hazards. Microgravity surveys involve precise gravitational field measurements along closed circuits across the islands. By comparing these measurements over time, we can identify local changes in the gravity field that may correspond to subsurface movements of magma or other density changes.

This work is focused on the volcanic islands of Tenerife, La Palma, Lanzarote, and El Hierro in the Canary Islands archipelago. These islands have experienced significant volcanic activity in the past centuries, making them ideal targets for using microgravity surveys as a volcano monitoring tool.  In this study, we conducted extensive surveys, collecting gravity data at numerous stations across the four islands. We realised periodic surveys consisting of 78 points in Tenerife, 22 points in La Palma, 7 points in Lanzarote and 19 points in El Hierro. The average spacing between measurement points is about 1.5 km in Tenerife and 2 km in the other islands. Field surveys are performed every 2 months in Tenerife and La Palma and every 6 months in the other islands.

Data are processed to correct the effects of tides, elevation and Bouguer anomalies and analysed to identify significant gravimetric anomalies. We created anomaly maps using Kernel Density interpolation, considering the differences between gravimetric values from one and a reference campaign. These maps visually represent the spatial distribution of gravimetric anomalies and enhance our understanding of the subsurface processes.

Applying microgravity surveys in volcanic regions like the Canary Islands offers an effective method for monitoring volcanic activity. This technique can complement other geophysical methods, such as seismic and geodetic measurements, to comprehensively understand volcanic processes. The results of this study contribute to the development of early warning systems for volcanic eruptions, ultimately aiding in the protection of local communities and infrastructure.