Frontal Aureole Deposit on Acheron Fossae ridge as evidence for landslide-generated tsunami on Mars

Abstract

The recurrent failures of the 8 to 10-km high basal scarp of the Olympus Mons volcano on Mars has resulted in enormous landslides merging into a composite deposit known as the aureole. The largest of these landslides, the western (W) aureole, appears as a hummocky and extensive tongue reaching the distance of 700 ​km from the present Olympus Mons edge. Totalizing a volume of 106 Km3, the W aureole was created by a single, 100°-wide sector collapse of the Olympus Mons flank between north and west directions. Whereas the western segment of the landslide fell onto the flat area of Amazonis Planitia, the northern section came across the gently sloping ridge of Acheron Fossae after 550 ​km of travel, and subsequently rose against slope for some additional 50–80 ​km.Analysis of imagery on Acheron Fossae ridge beyond the front of the landslide shows a peculiar deposit and associated morphologies. Termed here Frontal Aureole Deposits (FAD), it occurs in two units: a smooth, uniform deposit immediately beyond the aureole terminus, followed in the distal part by distinct lobes directed against slope. These deposits are interpreted as the remnants of debris-rich sandy and muddy waves thrust by the W aureole landslide that inundated the Acheron Fossae ridge. Numerical and analytical calculations set up to study the dynamics of inundation show that the length of the deposits was in the reach of water thrust by a fast-travelling landslide. A possible explanation for the presence of water is that the front was travelling across an outlet of the ancient Martian ocean which, consequently, must have persisted when the landslide event took place. According to this hypothesis, FAD represents the remnant of a giant tsunami deposit similar, albeit at a much larger scale, to those that occur on Earth.