Alaska's Mount Redoubt Volcano erupted on March 22, 2009, spewing ash into the atmosphere and obscuring the skies. Four more eruptions followed. According to scientists at the Alaska Volcano Observatory, the ash plume reached a height of 50,000 feet above sea level.
Because they happened at night, the eruptions could only be detected in thermal infrared imagery; high temperatures appear black, while lower temperatures are white. The ash plumes become very cold as they rise high in the atmosphere, making them appear white in the image. The MODIS instrument on NASA's Aqua satellite captured the image on March 23, just as the fifth eruption was about to start.