International audienceThe spatial and temporal coverage of measurements of previous termvolcanicnext term gas emissions remains patchy. However, over the last decade, emissions inventories have improved thanks to new measurements of some of the lesser-known previous termvolcanicnext term areas. We report on one such region - the Vanuatu island arc, in the Southwest Pacific - for which we now have sufficient systematic observations to offer a systematic emissions inventory. Our new estimate is based on SO2 flux measurements made in the period 2004-2009 with ultraviolet spectroscopy techniques for the following volcanoes: Yasur, Lopevi, Ambrym, Ambae, Gaua and Vanua Lava (from south to north). These are the first ever measurements for Lopevi, Gaua and Vanua Lava. The results reveal the Vanuatu arc as one of Earth's prominent sources of previous termvolcanicnext term degassing with a characteristic annual emission to the atmosphere of ~ 3 Tg of SO2 (representing about 20% of hitherto published global estimates). Our new dataset highlights the sustained prodigious degassing of Ambrym volcano, whose 5 Gg d-1 mean flux of SO2 represents nearly two-thirds of the total budget for the Vanuatu arc. This confirms Ambrym as one of the largest previous termvolcanic sources worldwide comparable to Etna, often considered as the most vigorous source of previous termvolcanic emission on Earth. We also report a high degassing for Ambae of ~ 2 Gg d-1 SO2, representing more than 28 % of the Vanuatu arc budget. Thus, 90 % of the SO2 output from Vanuatu is focused in the central part of the arc (from Ambrym and Ambae) where magmas originate from enriched Indian-type mantle and where peculiar tectonic conditions could favour high magma production rates

Volcanoes provide important contributions to atmospheric budgets of SO 2 and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18-270 kg s -1 of SO 2 , and 62-110 gs -1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of~8-14 and~27-50 kg s -1 , respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO 2 output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.

Yasur volcano has long been suspected as one of the volcanic emission sources responsible for a significant contribution of sulphur dioxide to the atmosphere. But due to its isolation in the south Pacific region, very little is known about its emission rates. We report here sulphur dioxide flux measurements, obtained on Yasur, using ultraviolet spectroscopy, from April 2004 to November 2005. We found an average flux of 7.9 kg.s−1 of SO2, which constitutes some 1–2% and 1.5–2.5% of estimated global time‐integrated volcanic emissions to the atmosphere and troposphere, respectively.

[1] The Yasur volcano in the Vanuatu archipelago is an outstanding source of infrasonic waves due to its regular activity. This volcano is permanently monitored by the IS22 infrasound station located in New Caledonia, about 400 km from it, and by one microbarometer installed close to its crater. A multiyear monitoring of Yasur is proposed to validate consistently the Naval Research Laboratory Ground to Space (NRL-G2S) semiempirical atmospheric model up to the stratosphere. The results of propagation modeling accurately explain seasonal changes as well as small short-timescale variations of the infrasonic observables. The azimuthal deviation is predicted with an uncertainty in general lower than 0.5°. The fluctuations of the trace velocity and the celerity are simulated with errors as large as 5 m/s. This study demonstrates that the use of appropriate propagation tools along with the NRL-G2S specifications provides accurate enough results for most of the long-range observations for the purpose of operational infrasound monitoring.