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
Maat Mons Maat Mons Maat Mons is a massive shield volcano. It is the second-highest mountain, and the highest volcano, on the planet Venus. It rises above the mean planetary radius at , and nearly 5 km above the surrounding plains. It is named after the Egyptian goddess of truth and justice, Ma'at. Maat Mons has a large summit caldera, 28×31 km in size. Within the large caldera there are at least five smaller collapse craters, up to 10 km in diameter. A chain of small craters 3–5 km in diameter extends some 40 km along the southeast flank of the volcano,