Monitoring of fumarole discharge and CO2 soil degassing in the Azores: contribution to volcanic surveillance and public health risk assessment

T. Ferreira T. Ferreira,F. Sousa F. Sousa,C. Faria C. Faria,F. Viveiros F. Viveiros,M. Marcos M. Marcos,J. L. Gaspar J. L. Gaspar

doi:10.4401/ag-3234

Abstract

Fluid geochemistry monitoring in the Azores involves the regular sampling and analysis of gas discharges from fumaroles and measurements of CO2 diffuse soil gas emissions. Main degassing areas under monitoring are associated with hydrothermal systems of active central volcanoes in S. Miguel, Terceira and Graciosa islands. Fumarole discharge analysis since 1991 show that apart from steam these gas emissions are CO2 dominated with H2S, H2, CH4 and N2 in minor amounts. Mapping of CO2 diffuse soil emissions in S. Miguel Island lead to the conclusion that some inhabited areas are located within hazard-zones. At Furnas village, inside Furnas volcano caldera, about 62% of the 896 houses are within the CO2 anomaly, 5% being in areas of moderate to high risk. At Ribeira Seca, on the north flank of Fogo volcano, few family houses were evacuated when CO2 concentrations in the air reached 8 mol%. To assess and analyse the CO2 soil flux emissions, continuous monitoring stations were installed in S. Miguel (2), Terceira and Graciosa islands. The statistical analysis of the data showed that some meteorological parameters influence the CO2 flux. The average of CO2 flux in S. Miguel stations ranges from 250 g/m2/d at Furnas volcano to 530 g/m2/d at Fogo volcano. At Terceira Island it is about 330 g/m2/d and at Graciosa 4400 g/m2/d.

Highlights

The Azores Archipelago comprises nine volcanic islands in the Atlantic Ocean where the American, African and Eurasian lithospher-During more than 500 years of history about thirty important destructive earthquakes and twenty-eight volcanic eruptions have been reported in the archipelago, causing thousands of Teresa Ferreira, João Luís Gaspar, Fátima Viveiros, Márcio Marcos, Carlos Faria and Fernando Sousa deaths and severe damage
This paper reports the fluid geochemistry monitoring programme that is being undertaken for volcanic surveillance and public health risk assessment in the region
CO2 soil concentration maps have been produced in the Azores for hazard and risk assessment

Summary

Introduction

The Azores Archipelago comprises nine volcanic islands in the Atlantic Ocean where the American, African and Eurasian lithospher-. During more than 500 years of history about thirty important destructive earthquakes and twenty-eight volcanic eruptions have been reported in the archipelago, causing thousands of Teresa Ferreira, João Luís Gaspar, Fátima Viveiros, Márcio Marcos, Carlos Faria and Fernando Sousa. The July 9, 1998 Faial earthquake (Senos et al, 1998) and the 1998-2001 submarine eruption west of Terceira Island (Gaspar et al, 2003) were the most recent events. Present-day volcanic activity in the Azores is marked by highly active fumarolic fields, hot springs and soils diffuse degassing phenomena. Special attention is given to the CO2 diffuse emissions whose significance in the total degassing of volcanic areas is of major importance (Allard et al, 1991)

Degassing areas

Sampling and analytical processes

Results

Methodology

Monitoring network and sampling

Future developments