A magmatic source for fumaroles and diffuse degassing from the summit crater of Teide Volcano (Tenerife, Canary Islands): a geochemical evidence for the 2004–2005 seismic–volcanic crisis

The present work reports the results of 15 studies of diffuse CO2 degassing performed at Teide Volcano crater (Canary Island, Spain) and the chemical and isotopic com- positions of fluids discharged from a fumarolic field located at the top of the volcano as measured between 1991 and 2010. A higher contribution of magmatic gases accompa- nied by enhanced total diffuse CO2 emissions were ob- served in relation with a seismic crisis that occurred in Tenerife Island between 2001 and 2005, with the main peak of seismic activity between April and June 2004. A signif- icant pulse in total diffuse CO2 emission was observed at thecrater of Teide (up to 26.3 t day−1) in 2001. In December 2003, the chemical composition of the Teide fumarole changed significantly, including the appearance of SO2, an increase in the HCl and CO concentrations and in the C2H6/ C2H4 and C3H8/C3H6 ratios, and a decrease in the H2S, CH4, and C6H6 concentrations and in the gas/steam ratio. A few months after a drastic decrease in seismic activity, the SO2, HCl, and CO concentrations and the C2H6/C2H4 and C3H8/C3H6 ratios strongly decreased, whereas the CH4 and C6H6 concentrations and the gas/steam ratios increased. According to the trends shown by both the geochemical parameters and the seismic signals late in the observation period, the risk of a rejuvenation of volcanic activity at Teide is considered to be low. The associated temporal changes in seismic activity and magmatic degassing indicate that geophysical and fluid geochemistry signals in this sys- tem are related. Future monitoring programs aimed at miti- gating volcanic hazard on Tenerife Island should involve coupled geophysical and geochemical studies.