Io's volcanic plains are shown in this archival image from NASA's Voyager 1, which spans an area about 1030 km (640 miles) from left to right. Numerous volcanic calderas and lava flows are visible.

Io's volcanic plains are shown in this Voyager 1 image, which spans an area about 1030 km (640 miles) from left to right. North is about the 1:30 position. Numerous volcanic calderas and lava flows are visible here. The brown teardrop-shaped feature at left center is Galai Patera, a 100-km-long (62 mi) lava-flooded caldera (collapsed vent) of a volcano. The composition of Io's volcanic plains and lava flows has not been determined. The prevalent yellow, brown, and orange material may consist dominantly of sulfur with surface frosts of sulfur dioxide or of silicates (such as basalt) encrusted with sulfur and sulfur dioxide condensates. The whitish patches probably are freshly deposited SO2 frost.

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