Gravity and spontaneous potential studies for volcano monitoring in Tenerife (Canary Islands)

Gravimetry and self-potential are passive geophysical techniques that can contribute to volcanic monitoring. The gravimetric method measures variations in the Earth's gravitational field due to density changes, which could be caused, for example, by magmatic intrusions and fluid accumulation. On the other hand, the spontaneous potential methods measure variations in the natural electric potential generated by the circulation of hydrothermal fluids related to the volcano dynamics. This technique is very useful to delineate the areas affected by hydrothermal activity. Combining both methods offers an integral perspective by detecting variations in mass distribution and natural electrical phenomena within the volcano. Therefore, their application allows us to see changes in the subsurface due to volcanic activity.

Applying these geophysical techniques in an active volcanic area could help better understand the temporal evolution of the volcanic activity. In this context, Tenerife represents the perfect scenario for applying these methods. This island consists of three ancient inactive volcanic systems (Anaga, Teno and Roques del Conde) located at the ends of the island, connected by three young rift zones to the center of the island where a giant volcanic caldera, known as Las Cañadas, is located. Inside the caldera and dominating the horizon is the Teide stratovolcano, which has a height of 3718 meters. The crater of Teide hosts intense hydrothermal activity with fumarole and relevant diffuse degassing.

For this purpose, since 2018, several gravimetric and spontaneous potential campaigns have been conducted each month on the island: from one side, 60 points spread over the three volcanic ridges, the caldera and the volcanic edifice of Teide were measured using a CG-6 Autograv™ Gravity Meter from SCINTREX. From the other side, 38 points distributed inside Teide’s crater were measured using a V-FullWaver datalogger from IRIS Instruments. The preliminary results show stable values for gravity, while for spontaneous potential, there are significant variations of the geoelectrical values due to variations in the hydrothermal activity.

We show how the continuous measurement of these parameters in time could contribute to the early identification of potential volcanic events in Tenerife, which is considered the island with the highest volcanic risk in the Canary Islands.