Abstract
We present daily measurements of sulfur dioxide (SO 2) emissions from active volcanoes in Ecuador and southern Colombia between September 2004 and September 2006, derived from the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite. OMI is an ultraviolet/visible spectrometer with an unprecedented combination of spatial and spectral resolution, and global coverage, that permits daily measurements of passive volcanic degassing from space. We use non-interactive processing methods to automatically extract daily SO 2 burdens and information on SO 2 sources from the OMI datastream. Maps of monthly average SO 2 vertical columns retrieved by OMI over Ecuador and S. Colombia are also used to illustrate variations in regional SO 2 loading and to pinpoint sources. The dense concentration of active volcanoes in Ecuador provides a stringent test of OMI's ability to distinguish SO 2 from multiple emitting sources. Our analysis reveals that Tungurahua, Reventador and Galeras were responsible for the bulk of the SO 2 emissions in the region in the timeframe of our study, with no significant SO 2 discharge detected from Sangay. At Galeras and Reventador, we conclude that OMI can detect variations in SO 2 release related to cycles of conduit sealing and degassing, which are a critical factor in hazard assessment. The OMI SO 2 data for Reventador are the most extensive sequence of degassing measurements available for this remote volcano, which dominated regional SO 2 production in June–August 2005. At Tungurahua, the OMI measurements span the waning stage of one eruptive cycle and the beginning of another, and we observe increasing SO 2 burdens in the months prior to explosive eruptions of the volcano in July and August 2006. Cumulative SO 2 loadings measured by OMI yield a total of ~ 1.16 Tg SO 2 emitted by volcanoes on mainland Ecuador/S. Colombia between September 2004 and September 2006; as much as 95% of this SO 2 may originate from non-eruptive degassing. Approximate apportionment of the total SO 2 loading indicates that ~ 40% originated from Tungurahua, with ~ 30% supplied by both Reventador and Galeras. These measurements of volcanic SO 2 degassing in Ecuador confirm OMI's potential as an effective, economical and risk-free tool for daily monitoring of SO 2 emissions from hazardous volcanoes.
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