5 Facts about Olympus Mons Volcano on Mars

A composite Viking orbiter image of Olympus Mons on Mars, the tallest known volcano and mountain in the Solar System.

Olympus Mons is a gigantic shield volcano on the planet Mars. A shield volcano is a volcano usually comprised of molten lava flows. The volcano has a height of over 72,000 ft measured by the Mars Orbiter Laser Altimeter. Olympus Mons is about 2.5 times Mount Everest’s height above sea level. It is one of the highest volcanoes, the tallest planetary mountain, and the second tallest mountain currently observed in the Solar System.

Here are 5 facts about Olympus Mons Volcano

  1. Size: Olympus Mons includes about 300,000 km2, which is roughly the size of the Philippines or Italy, and a 70 km thick lithosphere backs it. Why are the volcanoes on Mars so massive? Because the crust on Mars doesn’t move the way, it does on Earth. On Earth, the hot spots remain stable, but plates are moving above them. The Hawaiian islands rise from the northwesterly movement of the Pacific plate over a fixed hotspot producing lava. As the plate moves over the hotspot, new volcanoes are formed, and the existing ones become obsolete. This divides the total volume of lava among many volcanoes rather than one giant volcano. On Mars, the crust remains motionless, and the lava stacks up in an enormous volcano.
  2. Observation: Due to the size and lightweight slopes of Olympus Mons, an observer standing on the Martian surface would be incapable of seeing the volcano’s entire profile, even from a great distance. The curvature of the planet and the volcano itself would obscure such a synoptic view. Similarly, an observer near the summit would be unaware of standing on a very high mountain, as the slope of the volcano would reach far beyond the horizon, a mere 3 kilometers away.
  3. Pressure: The average atmospheric pressure at the top of Olympus Mons is 72 pascals, about 12% of the normal Martian surface pressure of 600 pascals. Both are remarkably low by terrestrial standards; by comparison, the atmospheric pressure at the summit of Mount Everest is 32,000 pascals or about 32% of Earth’s sea level pressure.
  4. Formation and Location: Olympus Mons rests at the corner of the Tharsis bulge, an ancient, broad volcanic plateau likely formed by the Noachian Period’s conclusion. During the Hesperian, when Olympus Mons started developing, the volcano was located on a shallow slope descended from the high in Tharsis into the northern lowland basins. Over time, these basins suffered large volumes of sediment decayed from Tharsis and the southern highlands. The sediments likely contained ample Noachian-aged phyllosilicates (clays) formed during an early period on Mars when surface water was abundant and was thickest in the northwest, where basin depth was most significant. As the volcano grew through parallel spreading, low-friction detachment zones preferentially formed in the more adhesive sediment layers to the northwest, creating the basal escarpment and broad lobes of aureole material. Spreading also transpired to the southeast; however, it was more restrained in that direction by the Tharsis rise, which granted a higher-friction zone at the volcano’s base. Friction was higher in that direction because the deposits were thinner and consisted of coarser-grained material immune to sliding. 
  5. Composition: The composition of Olympus Mons is roughly 44% silicates, 17.5% iron oxides (which give the planet its red coloration) 7% aluminum, 6% magnesium, 6% calcium, and unusually high proportions of sulfur oxide with 7%. These conclusions point to the surface being primarily composed of basalts and other mafic rocks, which would have exploded as low thickness lava flows, leading to the low gradients on the surface of the planet.

Source: “Olympus Mons”, NASA, Carr, Michael H. (11 January 2007). The Surface of Mars. Cambridge University Press, Wikipedia

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