With a summit nearly 27 km above its base, Olympus Mons is the highest volcano in the Solar System.
It was originally seen as a dark spot in the upper atmosphere of Mars following the arrival of Mariner 9.
Poking through the dust of a planet-wide storm.
In the early literature after its discovery it was called Nix Olympica.
With a basal diameter in excess of 500 km is can easily contain the entire Hawaiian Island chain.
Crater counts indicate that parts of the surface are relatively old (perhaps approaching 2 billion years)
while at the same time reveal areas devoid of craters at the scale of the highest resolution imagery.
Such a pattern would not be inconsistent with a volcano that is currently active and that has remained stationary
relative to the planetary interior for a significant period of time.
One particularly interesting feature is the cliff, most readily seen in the southeast quadrant.
Numerous, sometimes fanciful, hypotheses have been proposed for its origin.
Older lobate structures apparently underlie the main mass of the volcano.
These are particularly apparent to the north of the volcano.
Their much dissected nature has led to suggestions that they are ash-flow sheets.
The volcano sits close to the center of the Tharsis Dome
Much of the "recent" volcanic activity and structural deformation of Mars is associated with this latter feature.
The following stamps were issued as parts of miniature sheets by Sierra Leone in 1990
The printing was by lithography with a perf of 14.
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