# Quantification of low-temperature gas emissions reveals CO2 flux underestimates at Soufrière Hills volcano, Montserrat

## TL;DR

Measurements at Soufrière Hills volcano show that cold CO2 emissions are much higher than previously estimated, suggesting current methods underestimate volcanic CO2 fluxes.

## Contribution

This study reveals that traditional CO2 flux calculations significantly underestimate emissions due to cold CO2 degassing.

## Key findings

- CO2 flux from hot fumaroles was 15–41 kg/s, while the overall plume emitted 61–131 kg/s of CO2.
- Traditional methods underestimate CO2 flux by at least threefold due to cold emissions.
- Hydrothermal systems scrub 56–79% of HCl and 33–68% of SO2 from magmatic gases.

## Abstract

We performed helicopter-borne optical MultiGAS measurements of volcanic gas emissions from Soufrière Hills Volcano, Montserrat, revealing distinct spikes in SO2 and HCl concentrations within a larger CO2-rich plume. Acid-rich concentration spikes matched the distribution of high-temperature fumaroles, whereas CO2 is emitted broadly from high- and low-temperature fumaroles. The CO2 flux was 15 to 41 kilograms per second from hot fumaroles and 61 to 131 kilograms per second for the overall plume. The typical CO2 flux calculation of multiplying CO2/SO2 ratio with SO2 flux underestimates total CO2 flux by at least threefold. We quantified substantial magmatic gas scrubbing by the hydrothermal system, with 56 to 79% of initial HCl and 33 to 68% of initial SO2 lost. This study highlights the importance of precise acid-gas measurements for detecting heterogeneous degassing and suggests that traditional CO2 flux measurements may substantially underestimate contributions from cold CO2 degassing, leading to underestimated global volcanic fluxes.

Volcanic gas measurements at Soufrière Hills reveals cold CO2 emissions dominate volcanic flux, challenging established methods.