The Elysium volcanic province on Mars and the Tibesti volcanic province in Chad, Africa, were studied using Mariner 9, Landsat and Apollo photography. Elysium Mons on Mars and Emi Koussi on Earth show remarkable similarities in summit caldera and flank morphologies. Each has a large central caldera —12 km in diameter and from 500 to 1,000 m deep; both calderas contain numerous craters and large, irregular pits. Channel-like features which head at the calderas and taper downslope show evidence of collapse and possible lava erosion. Elysium Mons rises some 14 ± 1.5 km above its base, and the summit is about 20 km above the 6.1-mbar mean martian pressure surface. Crater size/frequency analysis indicates most of the craters are of endogenic origin. The subdued, hummocky terrain on the flanks are distinctly different from the slopes of the younger Tharsis Ridge volcanoes, showing little if any sign of recent material flow.
The lack of aqueous erosional forms on Elysium Mons argues strongly against recent (∼ 105 to 106 yr) pluvial episodes. The forms and associations of features throughout the Elysium region suggest that central volcanism started earlier in Elysium than in Tharsis and that the source of the Elysium volcanics has been chemically evolved, with evidence of silicic magma. Finally, the data are consistent with the view that the martian crust has been stable and essentially motionless for an extended period of martian geologic time.