This image taken by the High Resolution Stereo Camera (HRSC) shows the south western flank of Pavonis Mons, the central volcano of the three shield volcanoes that comprise Tharsis Montes. The image was obtained during orbit 902 on 2 October 2004 with a ground resolution of approximately 14.3 metres per pixel. The imaged region is at approximately 0.6° South and 246.4° East.
Pavonis Mons, rises roughly 12 km above the surrounding plains. Gently sloping shield volcanoes are shaped like a flattened dome and are built almost exclusively of lava flows.
The dramatic features visible in this image are located on the south western flank of the volcano. Researchers believe these are lava tubes, channels originally formed by hot, flowing lava that forms a crust as the surface cools. Lava continues to flow beneath this hardened surface, but when the lava production ends and the tunnels empty, the surface collapses, forming elongated depressions. Similar tubes are well known on Earth and the Moon.
Pit chains, strings of circular depressions thought to form as the result of collapse of the surface, are also visible within the image. In the northeast, there is a clear distinction between the brighter terrain at higher elevations and darker material located down slope. In the southwest, the lava tubes appear to be covered by subsequent lava flows.
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