Olympus Mons, on the planet of Mars, is the largest and youngest volcano in the solar system. Found in the Tharsis Montes region near the Martian equator, it is one of a dozen large volcanoes, many of which are ten to a hundred times taller than their terrestrial equivalents.
Olympus Mons, however, is the tallest of them all – towering 16 miles above the surrounding plains and stretching across 374 miles, roughly the size of the state of Arizona and would cover France.
It is also about 2.5 times the elevation of Mount Everest above sea level.
In comparison, Hawaii’s Mauna Loa, the tallest volcano on Earth, rises 6.3 miles above the sea floor, but its peak is only 2.6 miles above sea level. The volume contained by Olympus Mons is about a hundred times that of Mauna Loa and the entire Hawaiian island chain – from Kauai to Hawaii – that houses it could easily fit inside its Martian counterpart.
The volcano is a shield volcano, meaning rather than violently spewing molten material, they are created by lava flowing slowing down their sides. As a result, the mountain has a low, squat appearance, with an average slope of only five percent. Mauna Loa and Mauna Kea in Hawaii are both shield volcanoes and the largest active volcanoes on earth.
There are very few impact craters on the volcano’s surface, indicating that the uppermost layer of lava is still relatively young. The last eruption is thought to have occurred as recently as 25 million years ago. Therefore, there is a possibility that the volcano is still active and may erupt again in the future.
Six collapsed craters, and calderas, stack on top of each other to create a depression at the summit that is 53 miles wide.
“On Earth, the Hawaiian islands were built from volcanoes that erupted as the Earth’s crust slid over a hot spot — a plume of rising magma,” Jacob Bleacher, a planetary scientist at Arizona State University and NASA’s Goddard Space Flight Center, told Space.com. “Our research raises the possibility that the opposite happens on Mars; a plume might move beneath the stationary crust.”
Scientists think that the lower surface gravity of the planet, combined with higher eruption rates, allowed the lava on Mars to pile up higher, resulting in a volcano much larger than is possible on Earth. Tectonic plates could also play an important role in the different types of volcanoes: the hot spots of lava under the crust remain in the same location on both planets. On Earth, however, the movement of the crust prevents the steady buildup of lava.
On Mars, there is very little plate movement, meaning that instead of a chain of volcanic islands, large volcanoes such as Olympus Mons form.
Due to the size and shallow slopes of Olympus Mons, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance. The curvature of the planet and the volcano itself would obscure such a view. Similarly, an observer near the summit would be unaware of standing on a very high mountain as the slope of the volcano would extend far beyond the horizon – 1.86 miles away.
For context, for an 5ft 7in observer standing on the ground on Earth, the horizon is at a distance of 2.9 miles.
Olympus Mons and its neighbours in the Tharsis region stand high enough to reach above the frequent Martian dust storms recorded by observers as early as the 19th-century.
The astronomer Patrick Moore pointed out that Schiaparelli (1835–1910) “had found that his Nodus Gordis and Olympic Snow [Nix Olympica] were almost the only features to be seen” during dust storms, and “guessed correctly that they must be high”.