If you ask the geologist on guard how the mountains are formed, he is likely to tell you that the processes involved are associated with large-scale movements of the earth's crust (called plate tectonics). It will possibly talk about folding, faults, volcanic activity, igneous intrusion and metamorphism. It will be very interesting, no doubt, but the only problem is that this applies to a planet, the Earth. And on Mars the mountains are formed by the wind. Some, at least.
Source: APS Physics.
The Gale crater on Mars is 154 km in diameter and a mountain in its interior of 5,500 m altitude, Aeolis Mons. Curiosity is a human ingenuity the size of a utility car that is exploring the foothills of Aeolis Mons since August 2012. The Gale is a crater created by the impact of a meteorite about 3.7 billion years ago that was being filled with sediment for 500 million years, probably because it became a huge lake when Mars was still warm and humid.
Topographic map of the Gale crater (Mars). The circle indicates the landing area of the Curiosity rover. Source: APS Physics.
When this lake dried up, there was no mountain inside, but a cauldron filled with sediment. According to the simulations of William Anderson (University of Texas at Dallas) and Mackenzie Day (University of Washington in Seattle) there would have been whirlwinds of wind inside the walls of the crater that would have excavated a donut-shaped region, leaving a mountain in the center. As the winds would excavate one side of the crater faster than the other, it would result that the mountain is not in the center of the crater, but slightly displaced from the center.
Using fluid dynamics simulations, Day and Anderson studied wind flow patterns on four idealized crater geometries: a full crater, a crater filled with a shallow pit, a crater with a deep pit around the beginnings of a mountain , and an empty crater. These idealized craters had the main features of Gale and similar Martian craters.
Source: APS Physics.
Analyzing the wind patterns, the researchers observed that the winds were focused due to the topographic characteristics. Small-scale vortices develop when the wind first hits the outer edge of the crater rim. These vortices flow over the edge into the crater and then split into two streams that propagate to leeward (where the wind blows), a stream on either side of the rim of the crater. As the pit deepens and lengthens, the vortices increase in intensity.
The simulations indicate that the erosion begins at the place where the vortices enter the windward side (from where the wind blows) of the crater. The wind initially creates a half-moon depression that then lengthens and deepens until its two ends meet, creating a complete pit. The place where the wind hits the crater for the first time experiences the most lasting erosion, so the pit at that end of the basin is wider, and the mountain ends located to leeward of the center of the crater.
The results show that wind erosion can explain the formation and position of mountains within impact craters on Mars. Having a plausible scenario for the evolution of Gale's crater in the last 3 billion years will help interpret the geology data that is being collected by the Curiosity rover and in the reconstruction of the geophysical history of Mars.
Reference:
William Anderson and Mackenzie Day (2017) Turbulent flow over craters on Mars: Vorticity dynamics reveal aeolian excavation mechanism Phys. Rev. E doi: 10.1103/PhysRevE.96.043110
