Caractérisation et suivi du dégazage des principaux édifices volcaniques actifs de l'arc insulaire du Vanuatu par télédétection

Recent developments on UV spectrometer applications to volcanic degassing offer possibilities for regular measurement of the emission rates of isolated volcanoes whose SO2 output has never or rarely been measured: the only volcanic degassing measurements obtained in Vanuatu were taken in 1999 on just one of Vanuatu's 6 active aerial volcanoes. This thesis describes volcanic degassing studies carried out on 4 active volcanoes of Vanuatu. It brings to light permanent sources of SO2 and halogens on Ambrym and Yasur volcanoes. Degassing measurements were also performed during eruptive events on Aoba/Ambae and Lopevi. Overall results indicate that Vanuatu volcanoes are considerable sources of SO2 and halogens. These sources are related to cyclic and permanent manifestations; they were so far poorly documented, and not taken into account in the overall global assessments. A conservative estimate of the emission rate from these four active volcanoes (Aoba, Ambrym, Lopevi and Yasur) is of the order of 61 kg/s, which represents some 11 to 20 % of the global SO2 release into the atmosphere from volcanoes. Such quantities affect the local ecosystems and result in serious loss of plants and crops critical to the survival of Ni-Vanuatu populations; they occasionally endanger their health and safety. A better understanding of these volcanic gas emissions is an important factor in hazard mitigation for the Vanuatu island group.