Overview of SO2 degassing in Ecuadorian volcanoes: NOVAC Project 2007-2019

NOVAC, the Network for Observation of Volcanic and Atmospheric Change, started as a project involving the Instituto Geofísico (IG-EPN) in Ecuador in 2006. Initially, it allowed installation of four DOAS scanning instruments for SO ₂ flux monitoring at Cotopaxi and Tungurahua volcanoes, and today includes a total of 10 stations at six different volcanoes.

During eruptive activity of Tungurahua and Cotopaxi, SO ₂ emission measurements were a crucial complement to geophysical monitoring for understanding the volcanoes behavior and to guide assessment of possible eruptive scenarios. In particular, correlations of gas flux with seismicity and tephra volumes and componentry allowed to identify eruptive patterns during explosive and non-explosive periods of activity.

At Tungurahua, between 2007 and 2016, we were able to measure a total of 1.8 Mt of SO ₂ emitted to the atmosphere mostly during periods of active degassing. During quiescence phases, SO ₂ degassing was almost negligeable. For Cotopaxi, during the unrest and eruption that took place between April and December 2015, a total of 470 kt of SO ₂ have been emitted by the volcano. For both volcanoes, changes in the emissions amounts and patterns are well correlated with eruptive styles and seismic activity. On the contrary, SO ₂ emissions measured for Reventador volcano since 2017 are remarkably stable, despite changes in surface activity. At least a total of 210 kt of SO ₂ have been emitted by Reventador in the last two years. For other volcanoes, such as Sangay, Cayambe and Sierra Negra, measurements have served to define a baseline that will be useful in the event of future volcanic unrest .

We present an overview of these measurements which have become a critical component of daily monitoring efforts, both during periods of quiescence and eruption. As a result, Ecuador is one of the countries with larger number of volcanoes having continuous records of ground-based gas surveillance in the world.