5 April 2004
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows evidence of two collapsed lava tubes on the southeast flank of the giant martian volcano, Olympus Mons. One runs diagonally across the entire image, the other is shorter and does not extend across the whole image. The shorter one is a series of pits and troughs, rather than a continuous channel. Lava flowed in tubes under the surface; later, the roof of each tube collapsed to form a series of pits and troughs which, in the larger example, eventually coalesced to its present, channel-like form. The image is located near 16.8°N, 132.2°W, and covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.