First results of the Piton de la Fournaise STRAP 2015 experiment:multidisciplinary tracking of a volcanic gas and aerosol plume

The STRAP (Synergie Transdisciplinaire pour Répondre aux Aléas liés aux Panaches volcaniques) campaign was
conducted in 2015 to investigate the volcanic plumes of Piton de La Fournaise (La Réunion, France). For the first time,
measurements at the local (near the vent) and at the regional scales around the island were conducted. The STRAP 2015
campaign has become possible thanks to a strong cross-disciplinary collaboration between volcanologists and meteorologists.
The main observations during four eruptive 5 periods (85 days) are summarized. They include the estimates of SO2, CO2 and
H2O emissions, the altitude of the plume at the vent and over different areas of La Réunion Island, the evolution of the SO2
concentration, the aerosol size distribution, and the aerosol extinction profile. A climatology of the volcanic plume dispersion
is also reported. Simulations and measurements showed that the plume formed by weak eruption has a stronger interaction
with the surface of the island. Strong SO2 and particles concentrations above 1000 ppb and 50,000 cm−3, respectively, are
10 frequently measured over 20 km of distance from the Piton de la Fournaise. The measured aerosol size distribution shows the
predominance of small particles in the volcanic plume. A particular emphasis is placed on the gas-particle conversion with
several cases of strong nucleation of sulfuric acid observed within the plume and at the distal site of the Maïdo observatory. The STRAP 2015 campaign gave a unique set of multi-disciplinary data that can now be used by modellers to improve the
numerical paramameterizations of the physical and chemical evolution of the volcanic plumes.