A new strategy to measure radon in an active volcanic island (Tenerife, Canary Islands)

A promising tool in forecasting seismovolcanic activity is the analysis of temporal and spatial variations of soil gases, in particular radon (Rn-222). However, the modulation of the radon signal induced by environmental factors could mask information directly related to volcanic activity and, hence, radon sensors should be placed in locations where the number and effect of environmental parameters are minimised. There is a vast network of galleries, underground tunnels for deep-water prospecting, in the volcanic island of Tenerife, Canary Islands. They provide very stable conditions where radon monitoring could be carried out. In this sense, radon data were collected for 2 years at two different galleries in an attempt to assess the potential of these locations as observatories of the gas dynamics within the volcanic edifice of Tenerife. It turned out that natural ventilation, driven by temperature gradients between the air inside and outside the gallery, strongly disturbs the radon signal. We recommend to place detectors where the thermal gradient is minimised, namely far away from the entrance of the gallery or where internal temperatures are much higher than external air temperatures. In any case, we believe galleries are good places to monitor radon emissions in the island of Tenerife.