Abstract

A deep magmatic injection triggering a migration of fluid and gas at depth interacted with Las Cañadas Caldera aquifer is currently the most accepted origin for the seismic episode occurred in Tenerife in 2004. Aquifers in Tenerife are accessible at several locations by hundreds of galleries and wells, and by one of the scarce existing deep boreholes in the world tapping an aquifer close to an active volcano: the Montaña Majua Borehole (MMB), monitored since 1999 by the Tenerife Water Research Council (CIAT). To test the established hypothesis we have used the data set of MMB and galleries-wells provided by CIAT, to search for characteristic signatures of fluid-gas migration into Las Cañadas aquifer at the time of the anomalous seismic activity; i.e., we did not look for a precursory hydrogeochemical pattern of the seismicity, but we have investigated the response that the proposed processes should provoked to the aquifer. Data from MMB do not shown any notable change in water conductivity or temperature coincident with the alleged onset of a tremor in 18 May 2004 proposed by Almendros et al. (2007). Additionally, we did not find any correlation between the seismicity pattern and the recorded changes in water level, conductivity and temperature in MMB during 2004. The temporal irregularity of the hydrogeochemical dataset from water galleries-wells makes difficult its use for testing the magmatic-hydrothermal hypothesis. Besides, after a multivariate statistical study of 459 water analyses from 64 galleries-wells, we have not found in Las Cañadas or neighbour aquifers any relevant change in the hydrogeochemical parameters during 2004. From the results here presented, we propose that the nature of the seismic episode occurred during 2004 in Tenerife must be re-evaluated and other tecto-volcanic hypothesis must be tested using the invaluable data from MMB and water galleries.