A satellite chronology of the May–June 2003 eruption of Anatahan volcano

Abstract

The first recorded eruption of Anatahan began at approximately 17:00 local time on May 10, 2003. Here, we present observations made by a suite of Earth-orbiting satellites of the heat, ash and gas emitted from the volcano before, during and after the eruption. No thermal or sulphur dioxide emissions are apparent in MODIS (Moderate Resolution Imaging Spectroradiometer), AIRS (Atmospheric Infrared Sounder), EP TOMS (Earth Probe Total Ozone Mapping Spectrometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite images acquired prior to the eruption. However, within 24 h of eruption onset, the University of Hawaii's near-real-time satellite thermal monitoring system ‘MODVOLC’ detected the eruption and confirmed Anatahan's eastern caldera as the center of the activity. Although the eruption was initially phreatic, it quickly transitioned into a magmatic phase that culminated in the emplacement of a dacitic lava dome. The onset of the magmatic phase is recorded by MODVOLC as an order of magnitude increase in the heat flux from the volcano after May 16, indicative of fresh lava at the surface, relative to low values (50–90 MW) observed during the initial phreatic phase. MODVOLC detected thermal emission from the volcano on a further 22 occasions during the next 2 weeks, allowing us to quantitatively document temporal variations in thermal output during the eruption. We use MODIS, EP TOMS and AIRS data to document ash and sulphur dioxide emissions from Anatahan covering the period May 10–June 13, 2003. Using daily satellite observations in conjunction with ground-based estimates, we arrive at a total SO 2 discharge of ∼ 0.51 Mt for the ∼ 1 month of activity, of which ∼ 0.11 Mt was emitted during activity on May 10–12. Decreases in measured SO 2 flux prior to the observation of a lava dome on June 4 indicate that the emerging dome may have blocked the upper conduit and inhibited degassing during this period. A new episode of dome growth was detected by MODVOLC on April 12, 2004. So far, the level of thermal emission during the recent period of activity is substantially lower than that observed during the May–June 2003 eruption.