Spatial and Temporal Analysis of Temperature and Gaseous Emission Inside a Gallery in An Active Volcanic Island (Tenerife, Canary Islands)

Abstract

In Tenerife there are a vast number of sub-horizontal blind water mines, called “galleries”. Seven air and soil temperatures and CO2 concentration profiles in air were carried out inside the Río de Guía gallery (hereinafter RdG). An anomalous stable maximum temperature point (hereinafter MTP) was found around 2000 m from the entrance. During the warm period, a clear CO2 stagnation was detected before MTP, showing concentrations up to 14,000 ppm. In order to study gas emission and its dynamics inside the gallery, four stations were deployed around MTP. All stations recorded air and soil temperatures, and CO2 and Rn concentration in air from November 2009 to January 2011. After analyzing this dataset, it was possible to characterize the influence of MTP. This thermal anomaly divided the gallery into two sections. In the cold period, the outer section located outwards from MTP became colder while the inner section warmed up owing to a less heat transfer into the deepest part of the gallery. There were several short periods when variations in barometric pressure created an advection movement that was able to temporally change the gas behavior inside the gallery. Two soil gas samples were taken around MTP and their δ13C (CO2) ratios suggested a magmatic origin. All data were combined to create a model for the gas and thermal dynamics inside the gallery. This model, together with identification of background levels in each parameter, allows to identify any anomalous signal that could be elated with changes in volcanic activity.