On March 22, Alaska's Mount Redoubt erupted for the first time in 20 years, a violent event followed by a number of smaller emissions. Last Thursday it again erupted dramatically, this time spewing forth a cloud some 11 miles (18 kilometers) tall, according to pilot reports cited by the Alaska Volcano Observatory (AVO). That day Mount Redoubt was caught in the act by Landsat 5, a 25-year-old workhorse satellite used by NASA and the U.S. Geological Survey for Earth observation. The volcano's plume of steam is visible in the center of the photograph; the dark curve leading upward from the plume is lahar (volcanic debris mixed with meltwater) streaming through the Drift River Valley. For more images of the valley following the initial eruption, see our slide show of Redoubt photos from the AVO.