Diffuse CO2 degassing and low-temperature anomalies prior the 2014-15 Fogo eruption, Cape Verde

Abstract

The Cape Verde Islands are a group of 10 intraplate oceanic islands of which 3 show significant levels of recent volcanic activity: Fogo, Santo Antao and Brava. Of these, Fogo is the only historically active volcano with intense activity up to 1725 AD followed by less frequent, mainly effusive eruptions in the last 280 years. The last eruption began on 23 November 2014, and continuing until 8 February 2015. This eruption occurred 19 years after the previous eruptive event, but on the contrary of the 1995 eruption, when there was not monitoring program for the Cape Verde volcanic surveillance, a simple and multidisciplinary volcanic monitoring program, based on a collaborative research volcano monitoring program between Cape Verde and Spanish scientists, was operative to face volcanic unrest such as the 2014 eruption. As part of this volcano monitoring program, from May 2007 to January 2015, forty eight diffuse CO2 emission surveys were performed at the summit crater of Pico do Fogo, covering homogeneously an area of about 0.142 km2. Measurements of diffuse CO2 emission were performed at the surface environment following the accumulation chamber method. The emission rate was calculated after the construction of spatial distribution maps following the sequential Gaussian simulation (sGs) algorithm. The emission rate showed a first anomalous peak in the diffuse CO2 emission, suggesting the occurrence of a first magmatic reactivation likely due to a deep magma intrusion beneath Pico do Fogo volcano between November 2008 and February 2009. Diffuse CO2 emission data suggest the occurrence of a second magmatic intrusion that trigger the eruption process as can be observed by the significant increase of CO2 emission on March 2014. The increment of the diffuse CO2 emission rate shows a good temporal correlation with the satellite-based long-wavelength infrared data reported by Girona et al., (2021). The diffuse CO2 emission data and satellite-based thermal infrared radiance measurements prior the 2014-15 Fogo eruption demonstrate the importance of measuring both parameters to identify and evaluate changes in the volcanic activity of Pico do Fogo volcano. Girona, T. et al., (2021). Nature Geoscience 14, 238–241.