Olympus Mons
This picture clearly shows how large and flat Olympus Mons is. Although
the volcano is nearly 27 km high, it is over 20 times wider than it is
tall. Thus, most of the volcano has a fairly gentle surface slope. The
image also shows the distinct cliff which marks the base of Olympus Mons.
In places, this scarp is up to 6 km high. In other places, it is hidden
under lava flows cascading out into the surrounding lava plains. This
cliff is unique among the giant shield volcanoes on Mars. The rough,
crinkly patches around Olympus Mons are also unusual. They form the
Olympus Mons Aureole.
Both the Aureole and the basal cliff are poorly understood. However,
their origins may be related. In one theory, the basal cliff was formed
by many large landslides. The Aureole marks material piled up at the
bottom of these landslides.
Viking color mosaic, available Online from:
http://nssdc.gsfc.nasa.gov/image/planetary/mars/olympus_mons.jpg