This is an image of the Prometheus geyser.
Click on image for full size
Geysers of Io
When Voyager flew by Io the surprise discovery was the geyser, Prometheus, in full eruption. Geysers such as Prometheus spout pools of liquid around the vent, rather than a channel of lava. Features which resemble pools of liquid are readily seen on the surface of Io, suggesting a lot of geyser activity.
Geysers of Io spout liquid SO2 rather than water, and the spout rises quite high into the air. The average height of a spout of liquid SO2 is 300 km (200 mi)! The highest measured spout rose to 460 km (250 mi).
Well known geysers of Io include:
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