Theory on Martian volcano sizes

Abstract

A theory attributing the big difference in size between Martian and terrestrial volcanoes to the fact that the crust of Mars, in contrast to that of earth, remains fixed in place has been developed by U.S. Geological Survey scientist M. H. Carr on the basis of data from the Mariner 9 (1971) probe. For example, Olympus Mons, the largest volcano on Mars, is between 500 and 600 km across and ∼2 4 km high, whereas Mauna Loa, the largest volcano on earth, is 120 km across at its base on the ocean floor and more than 7000 m above the sea floor.According to Carr's theory (see his article in the Scientific American, January 1976 ), volcanoes that develop over ‘hot spots’ in the upper mantle just below the earth's crust are relatively short‐lived because they erupt and grow only so long as they remain over the hot spots in the stationary mantle. They become extinct as the motions of the crustal plates carry them away from the hot spots, and new volcanoes may form in the parts of the plates that drift over the hot spots. But on Mars, whose crust is not divided into moving plates, possibly because it is too thick to fracture, volcanoes remain for long periods over the hot spots and continue to erupt for long periods of time.