This volcano is comparable to Olympus Mons in horizontal extent but not in vertical relief; recent topographic maps show a total vertical relief of less than 7 km (4.2 mi) for Alba Patera. Just as the basal scarp is unique to Olympus Mons, Alba Patera is surrounded by a distinctive set of enormous fractures having a predominantly north-south orientation. The fractures have apparently been diverted around the central part of the Alba Patera complex. The low relief of Alba Patera may be due to the collapse of a structure comparable to the Olympus Mons shield but there is no direct evidence that such a collapse actually occurred. An alternative explanation for the low relief is that Alba Patera may include a significant portion of pyroclastic materials (ash) from its early history, caused by eruptions that are more explosive in nature than those typically associated with the effusion of lava flows. Alba Patera is older than the shield volcanoes in the Tharsis region and may represent a change in the style of centralized volcanic eruptions on Mars. The arrow indicates the lava flows shown in slide #10.
40 N, 110 W; Viking Orbiter frames 783A11 to 16, high-pass spatially filtered orthographic version.