Olympus Mons is a large shield volcano mountain that is located on the planet Mars and it has a morphology similar to the large volcanoes that make up the Hawaiian Islands. Rising to a height of 22 kilometres above the surrounding plains or 21 kilometres above the standard topographic datum of Mars, Olympus Mons is the tallest mountain known in the Solar System. This makes Olympus Mons stand at just under three times the height of
Mount Everest. The base of Olympus Mons measures over 600 kilometres across and the outer edge of the mountain is rimmed by an immense cliff which rises up to 8 kilometres above the surrounding terrain.
Due to the sheer size of Olympus Mons and from the fact that the average slope of the volcano’s flank is only 5 degrees, the entire vertical profile of Olympus Mons will not be visible to an observer who is standing at a great distance away on the surrounding plains as the curvature of the planet Mars would obscure the mountain’s summit. Similarly, an observer standing on the summit of Olympus Mons will be unable to view the surrounding plains as the slopes of the volcano would extend well beyond the horizon. However, the immense cliffs which surround almost the entire base of Olympus Mons will definitely make an impressive sight.
Olympus Mons is located on the northwestern edge of the Tharsis Bulge which also has some of the largest volcano mountains known in the Solar System. To the southeast of Olympus Mons are the mountains Arsia Mons, Pavonis Mons and Ascraeus Mons. Like Olympus Mons, these mountains are also immense shield volcanoes that rise to impressive heights, greatly dwarfing even the prominence of
Mount Everest. The Tharsis Bulge, on which these colossal mountains are located, covers millions of square kilometres in area and the height of Everest’s summit is merely comparable to the surface elevation of the massive plateau above the standard topographic datum of Mars.
The extraordinary size of Olympus Mons is due to the fact that unlike the Earth, Mars does not have plate tectonics and this enables the crust of Mars to remain stationary over a hotspot. By doing so, magma coming out of the hotspot continuously builds the volcano in the same location and allows Olympus Mons to become so large. A unique observational aspect of Olympus Mons is that it is sufficiently high enough to penetrate above the frequent Martian dust storms that can occasionally be large enough to engulf the entire planet. This was the first observational hint of the incredible height of Olympus Mons, long before the first spacecraft arrived in orbit around Mars.
The atmospheric pressure on the top of Olympus Mons is about 70 Pascal and this is about 11 to 12 percent of the atmospheric pressure at the standard topographic datum of Mars which has a value of 610 Pascal. In comparison, the atmospheric pressure on the top of Mount Everest is about 31400 Pascal while the atmospheric pressure at sea level on the Earth is 101325 Pascal. To put this into an Earthly perspective, the atmospheric pressure on the top of Olympus Mons is like being at an altitude of 50.5 kilometres above sea level while the atmospheric pressure at the standard topographic datum of Mars is like being at an altitude of 34.5 kilometres above sea level.
Orographic clouds that are made up of particles of water ice have long been known to be associated with Olympus Mons and with the other great volcano mountains on Mars. These clouds form when air masses are forced from a lower elevation to a higher elevation as they move up the slopes of these great mountains. The air masses cool as they rise and the moisture content carried within them condenses into particles of water ice, forming orographic clouds.