Conceptual model for the origin of the Olympus Mons cliffs, Mars: An essential influence of water?

Abstract

With a height of 21km above the mean Martian altitude and a diameter of 600km, the Olympus Mons of Mars is the highest and one of the largest volcanoes in the Solar System. It is a distinctive shield volcano, formed by stacked sequences of low-viscosity magma. Whereas the central part of the Olympus Mons exhibits slope angles of less than 1–5°, the periphery of the edifice terminates with steep cliffs sloping 12–15° up to 28°. Another remarkable feature is the aureole, a chain of crown-like deposits surrounding the edifice of Olympus Mons from an average distance of 400km. The aureole deposits, which lack any obvious analogue on the Earth, have been variously interpreted as volcanic products, pyroclastic or ash flows, slow deep-seated deformation, or catastrophic landslides.Numerical simulations and a comparative study of similar volcanic structures on Earth suggest that a volcanic edifice with the characteristics of Olympus Mons cannot be formed without the presence of water at the base. Because of the low cooling rate of lava in sub-aerial conditions, the superposition of purely subaerial lava flows would contribute with gentle slope to the topography. In contrast, the presence of a medium like water increases the convective heat exchange rate by nearly three orders of magnitude, thus stopping the lava flow and causing a slope increase at the borders of the edifice, which subsequently collapses. A model for the evolution of the Olympus Mons is consequently suggested in analogy with the Canary and the Hawaii island on Earth.