Olympus Mons Mars Artwork of Olympus Mons the largest known volcano in the Solar System It is found on Mars the fourth planet in our Solar System Its summit rises kilometres km above the surrounding plains Mount Everest is km high while the base measures km across resulting in a gentle surface slope Also visible is the cliff that marks the base of the slope The rough crinkly patchs around the volcanoe form the Olympus Mons Aureole Both the Aureole and the basal cliff are poorly understood although it is thought that their origins may be related