Figure 7-12 Io (a) This striking Galileo image of Io shows a variety of surface features including volcanoes, snow fields, and solidified lava flows. The range of colors results from surface deposits of sulfur ejected from Io’s numerous volcanoes. Plumes from the volcano Prometheus rise up 100 km (62 mi). Prometheus has been active in every image taken of Io since the Voyager flybys of 1979. (b) Photographed in 1999 and then 2000 (shown here), the ongoing lava flow from this volcanic eruption at Tvashtar Patera has considerably altered this region of Io’s surface. (c) Galileo image of an eruption of Pilan Patera on Io.