Melas, Candor and Ophir Chasmas in black and white
The collapse of large parts of the highland is an alternative explanation. For instance, extensive amounts of water ice could have been stored beneath the surface and were then melted as a result of thermal activity, most likely the nearby volcanic Tharsis province.
The water could have travelled towards the northern lowlands, leaving cavities beneath the surface where the ice once existed. The roofs could no longer sustain the load of the overlying rocks, so the area collapsed.
Regardless of how Valles Marineris might have formed, it is clear that once the depressions were formed and the surface was topographically structured, heavy erosion then began shaping the landscape.
Two distinct landforms can be distinguished. On one hand, we see sheer cliffs with prominent edges and ridges. These are erosion features that are typical in arid mountain zones on Earth.
Today, the surface of Mars is bone dry, so wind and gravity are the dominant processes that shape the landscape (this might have been much different in the geological past of the planet when Valles Marineris possibly had flowing water or glaciers winding down its slopes).
In contrast, some gigantic ‘hills’ (indeed, between 1000 and 2000 metres high) located on the floors of the valleys have a smoother topography and a more sinuous outline. So far, scientists have no definitive explanation for why these different landforms exist.
Map showing location of the chasmas in context
Below the northern scarp, there are several landslides, where material was transported over a distance of up to 70 kilometres. Also seen in the image there are several structures suggesting flow of material in the past. Therefore, material could have been deposited in the valleys, making the present floor look heterogeneous.
In the centre of the larger images above, there are surface features that appear similar to ice flows. These were previously identified in pictures from the US Viking probes of the 1970s; their origin remains a mystery.
Mars globe showing location of Melas, Candor and Ophir Chasma
The colour images were processed using the HRSC nadir (vertical view) and three colour channels. The perspective views were calculated from the digital terrain model derived from the stereo channels.
The 3D anaglyph image was created from the nadir channel and one of the stereo channels. Stereoscopic glasses are needed to view the 3D image. Image resolution has been decreased for use on the internet.
HRSC on the ESA Mars Express mission
The High Resolution Stereo Camera (HRSC) on the European Space Agency (ESA) Mars Express mission was developed by the German Aerospace Center (DLR) and built in cooperation with industrial partners (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The HRSC experiment on Mars Express is led by the Principal Investigator (PI) Prof. Dr Gerhard Neukum. The science team of the experiment consists of 45 Co-Investigators from 32 institutions and 10 nations.