These images are maps of the surface of Mars, showing where the volcanos are located.
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Image from: NASA

An Overview of Martian Tectonism

Unlike Earth, there is no plate tectonics on Mars. The Martian surface does not seem to have changed or moved in billions of years. The evidence for this fact can be found in two ways.

  • 1.) An examination of the surface of Mars shows cratering at all latitudes and longitudes. Craters are wiped out when the surface of a planet moves. Since cratering stopped soon after the solar system formed, about 4 billion years ago, a surface which still shows evidence of that catering has not changed in a very long time.
2.) Mars has several very large volcanos. When the surface of a planet moves, volcanos are moved aside as well. They are worn down, and eventually subducted below the surface. New volcanos arise to take the place of the ones which have been swept away. The Martian volcanoes became as large as they are because there was no plate tectonics to recycle the surface on which they were built.

The size of the volcanos also suggests that over its history, Mars has built a thick lithosphere, thick enough to support these very large volcanoes without allowing them to sink. A thick lithosphere would supress the motions of plates over a surface, even though the interior of the planet was warm enough for churning motions on the inside. Why would Mars, and not the Earth, have a thick lithosphere?

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