Volcanic Plumes

Voyager 2 took this picture of Io on the evening of July 9, 1979, from a range of 1.2 million kilometers (745,700 miles).  On the limb of Io are two blue volcanic eruption plumes about  100 kilometers (62 miles) high. These two plumes were first  seen by Voyager 1 in March 1979 and are designated Plume   5 (upper) and Plume 6 (lower). They apparently had been  erupting for a period of at least four months and probably longer. A total of six plumes were seen by Voyager 2, all of which were first seen by Voyager 1. Plume 1, the largest volcano viewed by Voyager 1, was no longer erupting when Voyager 2 arrived. Plume 4 was not viewed on the edge of Io's disc by Voyager 2 and, therefore, it is not known whether it was still erupting. (Courtesy NASA/JPL)