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
Highest unclimbed mountain Highest unclimbed mountain An unclimbed mountain is a mountain peak that has yet to be climbed to the top. Determining which unclimbed peak is highest is often a matter of controversy. In some parts of the world, surveying and mapping are still unreliable, and there are no comprehensive records of the routes of explorers, mountaineers and local inhabitants. In some cases, even modern ascents by larger parties have been poorly documented and, with no universally recognized listing, the best that can be achieved in determining the world's highest unclimbed peaks is somewhat speculative. Most sources indicate that Gangkhar Puensum ()