This image, taken by the High Resolution Stereo Camera on board ESA's Mars Express, shows Pavonis Mons, the central volcano of the three shield volcanoes that comprise Tharsis Montes.
Mars Express obtained the image using the HRSC during orbit 902 on Oct. 2, 2004, with a ground resolution of approximately 14.3 meters (46.5 feet) per pixel. The camera acquired the image at a location on Mars approximately 0.6 degrees south latitude and 246.4 degrees east longitude.
Pavonis Mons, rising roughly 12 kilometers (7.4 miles) above the surrounding plains – or roughly two miles higher than Mount Everest – is one of three gently sloping shield volcanoes shaped like flattened domes and built almost exclusively of lava flows.
The dramatic features visible in the color image are located on the southwestern flank of the volcano. ESA researchers think 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.
