How Mars Built a Giant Volcanic Region Without Plate Tectonics

Mars lacks plate tectonics, so volcanoes kept erupting in one region for billions of years, piling up lava until the crust was heavily stressed and fractured.

Astronomy

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Tharsis is a huge volcanic province near the equator of Mars, roughly 5,000 kilometers across and home to some of the largest volcanoes in the Solar System. The region grew over billions of years because Mars does not have Earth-style plate tectonics that continually moves the crust over long-lived volcanic sources. That allowed volcanic activity to remain concentrated in the same broad area for an extremely long time. The three major Tharsis Montes are Arsia Mons, Pavonis Mons, and Ascraeus Mons, while Olympus Mons sits just outside the main topographic bulge but is closely related to the wider volcanic province. The enormous amount of volcanic material placed on and within the crust produced major stresses and fractures across the region. Valles Marineris, the gigantic canyon system east of Tharsis, is widely understood to be associated with large-scale crustal rifting and stresses linked to the Tharsis rise. Tharsis also became so massive that scientists have proposed it influenced the orientation of Mars relative to its rotation axis through true polar wander. One influential estimate puts the mass of the Tharsis bulge at about 10 to the 21 kilograms, comparable to the mass of the dwarf planet Ceres. The exact history and structure of Tharsis remain active areas of planetary research, including debate over whether the region should be viewed as several volcanic systems or, in some models, as parts of one enormous spreading volcanic system.

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