- Rough, cratered terrain (which superficially resemble the
lunar highlands) which covers most of the southern hemisphere
and on average, is greater than 3 km above sea level. The
cratered regions are thought to be on the order of 3.9 billion years
old.
- Plains (sites of extensive lava flows) dominate the northern
hemisphere and typically lie below sea level. On the plains
the densities of large craters are 10 - 100 times lower than in the southern
hemisphere.The plains are thought to be on the order of 3 billion years old.
- The Tharsis Bulge is roughly
the size of North America, and was volcanically active, rising to a height of
~ 10 km above sea
level.
- The Tharsis Bulge is the least cratered and so, the youngest part of the Mars's surface. Tharsis probably started to form ~3.9 billion years ago, but has been active until fairly recently (perhaps as recent as several hundred million years ago). The crater density on Tharis suggests that most features are 2-3 billion years old. Near the top of the Tharsis Bulge, there are three shield volcanoes, each rising 18 km to elevations of 27 km with bases of size 400 kilometers. An even larger volcano, Olympus Mons rises 25 km above the northwestern slope of Tharsis to reach the same height as the Tharsis volcanoes, 27 km above sea level. Olympus Mons is nearly 700 km across its base, roughly the size of France and may have been active as recently as 100-300 million years ago. The largest Hawaiian volcano is ~200 km across its base and ~ 9 km high (similar in elevation to Maxwell Montes on Venus). The difference in the maximum height of volcanos on the Terrestrial planets is a consequence of the weaker surface gravity on Mars and lack of large scale horizontal plate motion.
- The Tharsis volcanoes are shield volcanoes so
the fact that they are concentrated in one region
====> at the time the volcanos formed there
was not large scale crustal movement or, at best, only slow motion
- The slopes of the volcanos are not heavily cratered at all (because of flowign lava) indicating that the volcanoes may have been active within the last few hundred million years ====> Mars was likely geologically active in recent times (however, without plate tectonic activity)
Videos of Rover: Spirit to Mars, Egress 1, Egress 2, Drive
When considering the surfaces of planets, one is naturally led to consider analogues of the oceanic and continental regions of the Earth. In this spirit, the surface of Mars can be divided up into two types of terrain.
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An interesting region which straddles the two zones is the Tharsis Bulge.
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Note that:
Near the Tharsis Bulge is Valles Marineris, part of an interconnected system of east-west running canyons approximately 4,000 km long. The individual canyons are 3 km deep, but in the center of the canyon, the depression is nearly 7 km and more than 500 km wide. The Grand Canyon would fit easily into one of the tributaries of the Valles Marineris. These features likely started to formed around 3.5 - 3.9 billion years ago, but based on crater densities, the last work apparently took place around 2 billion years ago.
The Tharsis Bulge was thought to have formed through an uplift (vertical rise) of the crust of Mars. The Valles Marineris was also probably due to some sort of crust cracking driven by crustal motion. It was not cut by flowing water (as was the Grand Canyon).
