The Tungurahua volcano in the South American country of Ecuador began erupting on April 21, 2011, spewing gases and volcanic ash in a plume that extends 125 km west of the summit. This imagery shows the evolution of the volcanic plume since April 21, as detected by the NASA Aura satellite's OMI sensor. The Ozone Mapping Instrument is able to detect the sulfur dioxide gases associated with volcanic eruptions. The areas with the highest concentration of sulfur dioxide are colored bright yellow. This data is processed and analyzed by the Washington Volcanic Area Advisory Center, operated by NOAA.