the large caldera. This phase ended with an eastward tilting of the summit dome, which may have initiated additional graben formation in Alba Fossae. The last volcanic features to form were the small shield and caldera at the summit. Much later, between about 1,000 and 500 million years ago, a final stage of faulting occurred that may have been related to dike emplacement and the formation of pit crater chains. Classification The classification of the Alba Mons volcano is uncertain. Some workers describe it as a shield volcano, others as a lowland patera (in contrast to highland paterae, which are low-lying ancient volcanoes with furrowed ash deposits located in the southern Martian highlands), and still others consider it a one-of-a-kind volcanic structure unique to Mars. Some researchers have compared Alba Mons to coronae structures on the planet Venus. Alba Mons shares some characteristics with the Syrtis Major volcanic structure. (See Volcanism on Mars.) Both volcanoes are Hesperian in age, cover large areas, have very low relief, and large shallow calderas. Also like Alba, Syrtis Major displays ridged tube- and channel-fed lava flows. Because Alba Mons lies antipodal to the Hellas impact basin, a few researchers have conjectured that the volcano's formation may have been related to crustal weakening from the Hellas impact, which produced strong seismic waves that focused on the opposite side of the planet. Interactive Mars map See also Geography of Mars Geology of Mars List of mountains on Mars by height Tamu Massif Volcanism on Mars References Further reading Boyce, Joseph, M. (2008). The Smithsonian Book of Mars; Konecky & Konecky: Old Saybrook, CT, Carr, Michael, H. (2006). The Surface of Mars; Cambridge University Press: Cambridge, UK, . Cattermole, Peter, J. (2001). Mars: The Mystery Unfolds; Oxford University Press: Oxford, UK, . Frankel, Charles (2005). Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io; Cambridge University Press: Cambridge, UK, . Hartmann, William, K. (2003). A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet; Workman: New York, . Morton, Oliver (2003). Mapping Mars: Science, Imagination, and the Birth of a World; Picador: New York, . External links View of Albra Mons in context in view extending from the North pole down, taken by Mars Express in 2017 Mountains on Mars Polygenetic shield volcanoes Volcanoes of Mars Arcadia quadrangle Diacria quadrangle Tharsis quadrangle