Elevated CO2 Emissions during Magmatic-Hydrothermal Degassing at Awu Volcano, Sangihe Arc, Indonesia

Philipson Bani,Kristianto Kristianto,Alessandro Aiuppa,Marcello Bitetto,Etienne Le Glas,Devy Kamil Syahbana

doi:10.3390/geosciences10110470

Abstract

Awu is a remote and little known active volcano of Indonesia located in the northern part of Molucca Sea. It is the northernmost active volcano of the Sangihe arc with 18 eruptions in less than 4 centuries, causing a cumulative death toll of 11,048. Two of these eruptions were classified with a Volcanic Explosivity Index (VEI) of 4. Since 2004, a lava dome has occupied the centre of Awu crater, channelling the fumarolic gas output along the crater wall. A combined Differential Optical Absorption Spectroscopy (DOAS) and Multi-component Gas Analyzer System (Multi-GAS) study highlight a relatively small SO2 flux (13 t/d) sustained by mixed magmatic–hydrothermal emissions made-up of 82 mol.% H2O, 15 mol.% CO2, 2.55 mol.% total S (ST) and 0.02 mol.% H2. The CO2 emission budget, as observed during a short observation period in 2015, corresponds to a daily contribution to the atmosphere of 2600 t/d, representing 1% of the global CO2 emission budget from volcanoes. The gas CO2/ST ratio of 3.7 to 7.9 is at the upper limit of the Indonesian gas range, which is ascribed to (i) some extent of S loss during hydrothermal processing, and perhaps (ii) a C-rich signature of the feeding magmatic gas phase. The source of this high CO2 signature and flux is yet to be fully understood; however, given the peculiar geodynamic context of the region, dominated by the arc-to-arc collision, this may result from either the prolonged heating of the slab and consequent production of carbon-rich fluids, or the recycling of crustal carbon.

Highlights

The Indonesian archipelago is one of the Earth’s most active volcanic arc segments, but yet one whose volcanic gas contribution into the atmosphere remains poorly constrained due to access difficulties
Volcanic gas emissions were measured only at a few volcanoes, initially using conventional techniques such as Giggenbach bottles and Correlation Spectrometer (COSPEC). This was the case for Merapi, Tangkuban Perahu, Papandayan, Dieng, Lewotolo and Bromo [1,2,3,4]
Initial Indonesian arc-scale volcanic SO2 emission budget estimates were based on the interpolation of sparse field measurements [2,16,17,18], resulting in large emission ranges between 0.07 and 2.6 Tg/yr

Summary

Introduction

The Indonesian archipelago is one of the Earth’s most active volcanic arc segments, but yet one whose volcanic gas contribution into the atmosphere remains poorly constrained due to access difficulties. Volcanic gas emissions were measured only at a few volcanoes, initially using conventional techniques such as Giggenbach bottles and Correlation Spectrometer (COSPEC). This was the case for Merapi, Tangkuban Perahu, Papandayan, Dieng, Lewotolo and Bromo [1,2,3,4]. Initial Indonesian arc-scale volcanic SO2 emission budget estimates were based on the interpolation of sparse field measurements [2,16,17,18], resulting in large emission ranges between 0.07 and 2.6 Tg/yr. Recent measurements are based primarily on Geosciences 2020, 10, 470; doi:10.3390/geosciences10110470 www.mdpi.com/journal/geosciences

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