New perspectives on volcano monitoring in a tropical environment: Continuous measurements of soil CO2 flux at Piton de la Fournaise (La Réunion Island, France)

Detecting renewal of volcanic activity is a challenging task and even more difficult in tropical
settings. Continuous measurements of soil CO2 flux were carried out at the Piton de la Fournaise volcano
during 2013–2016. Since this site is in the tropics, periods of heavy rainfall are in the norm. Measurements
covered volcanic unrest after a hiatus of 3.5 years. We find that while temperature has the strongest effect,
extreme rainfall causes short-term noise. When corrected and filtered from the environmental influence, soil
CO2 time series permit to detect a major deep magmatic event during March–April 2014, 3 months before the
first eruption of the new activity phase. Correlation with geophysical data sets allows timing of further stages
ofupwardfluidascent.OurstudyvalidatessoilCO2fluxmonitoringintropicalenvironmentsasavaluabletoolto
monitor magma transfer and to enhance understanding of volcano unrest down to the lithospheric mantle.