Unsteady thermo-fluid-dynamics modelling of Timanfaya volcanic area (Lanzarote,Canary Islands) and present-day ground deformation

Lanzarote is the most northeast and together with Fuerteventura is the oldest island of the Canarian Archipelago (Spain), which is located on a transitional zone, a passive margin, between oceanic and continental crust. The last volcanic eruption in Lanzarote was a 7 years voluminous eruptive cycle, occurred during the 18^th century. Historical seismicity registered in the region, is customarily attributed to diffuse tectonic activity.

This study is intended to contribute to understanding the surface thermal anomalies and the active tectonics on Lanzarote island, mainly in the Timanfaya volcanic area, which is located to the southwest of the island and covers the land extension generated by the last eruption..

First, we describe the steps taken to implement a thermo-fluid-dynamics model to study the surface thermal anomalies detected at the Timanfaya volcanic area after the volcanic activity that took place between 1730 and 1736. The origin of these anomalies is acknowledged to be due to the intrusion of a magma body and its consequent cooling, but which still might have very high temperature. This hypothesis is based on the fact that the cooling of basaltic magma, which has an initial temperature of 1200 °C, takes about 10⁴ ÷10⁵ years, as indicated by some authors. Our physical model consists of a cooling magma body, with a radius of 300 m, located at a depth of 4 km and with a temperature of 800 degrees (1073,15 K).

The model was developed in three steps: 1) accounting for the energy balance only, 2) both the energy and the momentum balance are accounted for, 3) mass balance is accounted too.

The three thermo-fluid dynamic models are based on a finite element modelling (FEM). The novelty of our model consists in including both the steady and unsteady (transient) phase, not considered in analytical solutions under purely stationary conditions developed in past modelling by other authors.

Second, we describe a detailed geodetic continuous monitoring in Timanfaya volcanic area, where, as mentioned, the most intense geothermal anomalies of Lanzarote are located.

We report on the analysis of about 6 years of CGNSS data collected on a small network consisting in 9 permanent stations, spread over Timanfaya area in Lanzarote Island. The GNSS stations are operated by several owners: the Institute of Geosciences, IGEO, DiSTAR, the Geodesy Research Group of University Complutense of Madrid, the Cartographical Service of the Government of Canary Islands and the National Geographic Institute of Spain.

Finally, we attempt to interpret the thermo-fluid dynamic model and the observed ground deformations in light of the tectonic framework derived from state-of-the-art geophysical studies.