Satellite observations of environmental changes from the Tonga volcano eruption in the southern tropical Pacific

Abstract

Satellite measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua were used to study changes of the ocean and atmosphere following the eruption of a submarine volcano in March 2009 in the southern tropical Pacific. Significant increase of water turbidity was observed in an area of ∼368 km2 near the location of the eruption due to the deposition of volcanic ash. In the ocean region close to the volcanic eruption, the diffuse attenuation coefficient at a wavelength of 490 nm, K d(490), increased from ∼0.025 to 0.16 m−1 before and after the volcanic eruption. Within two weeks of the event, the coverage of the ash-laden waters decreased to ∼30 km2, and after four weeks the satellite-measured marine environment parameters returned back to the pre-eruption condition. The normalized water-leaving reflectance spectra, derived from the combined near-infrared (NIR) and shortwave infrared (SWIR) atmospheric correction algorithm for the ash-laden water, show some unique optical features, different from those of the sediment-dominated turbid waters, river plume waters or other productive waters. No significant sea surface temperature (SST) change was detected from satellite measurements near the eruption site. Volcanic ash plumes in the atmosphere were observed moving north-eastward following the ocean winds on 18 March 2009. The aerosol optical thickness increased from 0.06 on the previous day to 0.25 at a location ∼60 km north-east of the volcanic eruption site.