Olympus Mons the height of Mauna Kea as measured from its base on the ocean floor). The total elevation change from the plains of Amazonis Planitia, over to the northwest, to the summit approaches . The summit of the mountain has six nested calderas (collapsed craters) forming an irregular depression × across and up to deep. The volcano's outer edge consists of an escarpment, or cliff, up to tall (although obscured by lava flows in places), a feature unique among the shield volcanoes of Mars. Olympus Mons covers an area of about , which is approximately the size of Italy, and it
Mons Huygens Mount Fuji, which overlooks Tokyo, Japan, is about altitude. Compared to the Andes, Mons Huygens would rank outside the hundred tallest peaks, being roughly the same height as Argentina's Cerro Pajonal; the peak is higher than any above sea level in Oceania, but base-to peak it is considerably shorter than Hawaii's Mauna Kea and its neighbors. Mons Huygens Mons Huygens is the Moon's tallest mountain (but not its highest point). It is about high and is located in the Montes Apenninus. The Montes Apenninus were formed by the impact that created Mare Imbrium. Adjacent is Mons Ampère to the west.