At a height of 25km, Olympus Mons on Mars is the largest volcano in the Solar System and is nearly three times as tall as Mount Everest.
It is thought that one of the reasons that Olympus Mons and the other volcanoes on Mars are large is that the Red Planet's crust doesn't move like the Earth's. This lack of active plate tectonics means that rising magma erupted on the same part of the planet's crust and slowly built up a very large volcano.
Eruptions of Olympus Mons and the other volcanoes on Mars are thought to have ceased due to the cooling of Mars's core.
Photo: Olympus Mons taken by the Mars Global Surveyor probe (NASA/JPL/Malin Space Science Systems)
Mars has the Solar System's largest volcano.
The probe sees Mars's moons, volcanoes.
Viewing parts of Mars missed by previous probes, Mariner 9 revealed three huge volcanoes and a massive canyon, now estimated to be 5 miles (8km) deep and over 1,800 miles (3,000km) long. The probe also took photographs of Mars's moons, Phobos and Deimos.
Brian Cox describes the Solar System's largest volcano.
Professor Brian Cox describes the biggest volcano in the Solar System, Olympus Mons on Mars.
Why does Mars have volcanoes that are so much bigger than Earth's?
Professor Iain Stewart looks at some of the reasons why Martian volcanoes such as Olympus Mons are so much bigger than Earth's.
A series of missions finds astonishing features on the Red Planet.
The unmanned Mariner missions gradually revealed Mars's extreme landforms. Perhaps most impressive was Olympus Mons, a volcano three times the size of Mount Everest.
Olympus Mons (Latin for Mount Olympus) is a large shield volcano on the planet Mars. By one measure, it has a height of nearly 22 km (14 mi). Olympus Mons stands almost three times as tall as Mount Everest's height above sea level. It is the youngest of the large volcanoes on Mars, having formed during Mars's Amazonian Period. It had been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Olympic Snow"). Its mountainous nature was suspected well before space probes confirmed its identity as a mountain.
The volcano is located in Mars's western hemisphere at approximately 18°39′N 226°12′E / 18.65°N 226.2°E / 18.65; 226.2, just off the northwestern edge of the Tharsis bulge. The western portion of the volcano lies in the Amazonis quadrangle (MC-8) and the central and eastern portions in the adjoining Tharsis quadrangle (MC-9). Two impact craters on Olympus Mons have been assigned provisional names by the International Astronomical Union. They are the 15.6 km (9.7 mi)-diameter Karzok crater (18°25′N 131°55′W / 18.417°N 131.917°W / 18.417; -131.917) and the 10.4 km (6.5 mi)-diameter Pangboche crater (17°10′N 133°35′W / 17.167°N 133.583°W / 17.167; -133.583). The craters are notable for being two of several suspected source areas for shergottites, the most abundant class of Martian meteorites.