Changes in the thermal energy and the diffuse 3He and 4He degassing prior to the 2014–2015 eruption of Pico do Fogo volcano, Cape Verde

Abstract

We report the temporal evolution of helium isotopes emission and thermal energy release in the period 2007–2018 at the summit crater of Pico do Fogo volcano, Cape Verde. 3He/4He ratio measured in a fumarolic discharge, ranged from 6.69 to 8.63 RA, being the maximum mantle-derived composition measured in November 2013, one year before the eruption onset in 23 November 2014, and confirm the beginning of a possible magmatic intrusion four years and eight months before the 2014–2015 eruption. 3He and mantle 4He emission rates showed similar trends in temporal evolution. Thermal energy release calculated for the study period ranged from 1 up to 72 MW, being the maximum values linked to maximum 3He (1.7 × 10−2 and 1.5 × 10−3 mol d−1 using the first and the second approach respectively), confirming a close relationship between both parameters. After the eruptive event, a simultaneous decrease in RA, 4He and 3He emissions is observed due to the rapid degassing of the magma responsible of the 2014–2015 eruptive process.