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Olympus Mons stands 24 km tall and is nearly 600 km in diameter. The adjoining Tharsis Montes consists of Ascraeus, Pavonis, and Arsia. Alba Mons, at the northern end of the Tharsis plateau, is 1500 km in diameter, and stands 6 km above the surrounding plains. In comparison, Mauna Loa is merely 120 km wide but stands 9 km above the sea floor. [4]
The northern part is an enormous topographic depression. About one-third of the surface (mostly in the northern hemisphere) lies 3–6 km lower in elevation than the southern two-thirds. This is a first-order relief feature on par with the elevation difference between Earth's continents and ocean basins. [12]
Mars hosts many enormous extinct volcanoes (the tallest is Olympus Mons, 21.9 km or 13.6 mi tall) and one of the largest canyons in the Solar System (Valles Marineris, 4,000 km or 2,500 mi long). Geologically , the planet is fairly active with marsquakes trembling underneath the ground, dust devils sweeping across the landscape, and cirrus clouds .
The difference between Mars's highest and lowest points is nearly 30 km (from the top of Olympus Mons at an altitude of 21.2 km to Badwater Crater at the bottom of the Hellas impact basin at an altitude of 8.2 km below the datum).
A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars. [9] Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through.
The maps below were produced by the Mars Global Surveyor ' s Mars Orbiter Laser Altimeter; redder colors indicate higher elevations.The maps of the equatorial quadrangles use a Mercator projection, while those of the mid-latitude quadrangles use a Lambert conformal conic projection, and the maps of the polar quadrangles use a polar stereographic projection.
Relatively early in its history, Mars lost its magnetic field, which allowed the solar wind to claw away most of its atmosphere; with that, much of the water sublimed into space.
The same methodology was later applied to the Moon [1] and then to Mars. [2] Another stratigraphic principle used on planets where impact craters are well preserved is that of crater number density. The number of craters greater than a given size per unit surface area (usually a million km 2) provides a relative age for that surface. Heavily ...