• Mars;
  • south polar;
  • Dorsa Argentea Formation;
  • subglacial volcanism;
  • Hesperian

[1] A number of isolated mountains mapped in the south polar region of Mars are documented using Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) and Mars Orbiter Camera (MOC) data. These mountains have average separation distances of ∼175 km, they are typically 30–40 km in diameter and 1000–1500 m high, and their bases fall near an elevation of ∼1200 m. A significant number of the population are located on or very close to a 660 km long line extending toward the south pole. The summits of a number of these mountains have unusual shapes: flat-topped, flat-topped with a cone, and large summit craters relative to the summit diameter. Sinuous channels are found in association with the margins of several of the mountains. Several modes of origin are considered for these mountains, including impact, tectonic, and volcanic. These mountains occur in intimate association with the Hesperian-aged Dorsa Argentea Formation, a unit containing features and structures interpreted to be related to a thick, areally extensive ice sheet. On the basis of these observations and analyses it is concluded that the most plausible origin for these mountains is volcanic and that they represent extrusion of lava from vents, many of which lay underneath an ice sheet. The unusual shape of many of the mountains is consistent with construction of a volcanic edifice underneath an ice sheet and melting of adjacent ice-rich material, sometimes forming drainage channels. The topography of these mountains suggests that the ice sheet averaged at least 1.4 km thick at the time of eruption. These features appear to be associated with Early Hesperian-aged ridged plains (Hr).