An enormous plume of liquid sulfur dioxide rises more 200 miles above Io's calamitous surface. So large is this eruption that the source of the geyser lies beyond the horizon. In the foreground are the remains of old lava flows composed of silicate rocks, sulfur, and sulfur compounds. Io has a thin atmosphere composed of sulfur dioxide and is very cold (with the exception of the volcanic calderas themselves) with a surface temperature of - 225º F.

Io is the most volcanically active body known in the Solar System. Eruptions are so common and so large that Io has likely resurfaced itself many times since its formation. As a result, impact craters, which are common on many planets and satellites, are absent on Io.