Mars is home to the tallest volcano in the solar system, a colossal mountain called Olympus Mons that dwarfs anything on Earth. Rising roughly 16 miles from base to summit, it stands close to three times the height of Mount Everest and covers an area comparable to a large country.
The dimensions of a record-setting mountain
Everest reaches about 5.5 miles above sea level, or 8.8 kilometers, measured from the ocean surface. Olympus Mons climbs far higher, with its peak sitting somewhere between about 13 and 16 miles above the surrounding plains depending on where the base is drawn, or roughly 22 kilometers above the Martian reference level. Even the more conservative measurement leaves it towering over any peak on Earth, and the base-to-summit figure is what places it near the “three times Everest” mark. Its footprint spans hundreds of miles across, wide enough to blanket a state the size of Arizona, and the summit is crowned by a complex of overlapping collapse craters, called a caldera, tens of miles wide.
Why it is a shield, not a spire
Despite its height, Olympus Mons is not a steep, jagged peak. The record for Olympus Mons describes it as a shield volcano, built up over eons by countless flows of runny lava that spread out in thin sheets rather than piling up steeply. The result is a broad, gently sloping dome with an average incline of only about five degrees, so a person standing on its flank might not even perceive that they were on a mountain at all. A steep cliff, or escarpment, several miles high rings much of its outer edge, marking where the volcano’s bulk drops away to the plains. The same gentle profile can be seen in Earth’s shield volcanoes, such as those that form the Hawaiian Islands, though Olympus Mons dwarfs them many times over.
The Martian conditions that let it grow
A mountain this large could not form on Earth, and the reasons trace to two differences between the planets. As explained in the overview material from NASA’s Mars science pages, Earth’s crust is broken into moving tectonic plates. A hot plume of magma beneath the surface builds a volcano, but the plate slides along over millions of years, so the plume punches a chain of separate, smaller volcanoes instead of one giant. Mars appears to lack that plate motion, so the crust sat still over the hot spot and a single vent erupted in the same place for an immense span of time, stacking flow upon flow. Lower Martian gravity, about a third of Earth’s, also allowed the structure to rise higher before its own weight would cause it to spread or collapse.
A member of the Tharsis volcanic family
Olympus Mons does not stand alone. It sits at the edge of a vast raised region called the Tharsis bulge, which hosts several other enormous volcanoes, including three giants lined up in a row known as the Tharsis Montes. This concentration of volcanism deformed a large fraction of the planet’s surface and may have influenced the entire Martian climate in the distant past by pumping out gases and reshaping the crust. The whole province tells the story of a world that was once far more volcanically active than it is today, and the sheer volume of rock piled into Tharsis was enough to weigh down and warp the crust across much of the planet.
What the volcano reveals about Mars
The very existence of such a mountain is a clue to Martian history. Its size implies long periods of sustained eruption and a crust strong and stable enough to bear the load, while the relatively small number of impact craters on parts of its surface suggests some lava flows are, in geological terms, comparatively young. Whether Mars is truly dead volcanically or merely dormant is a question scientists continue to probe, using orbiters and landers to search for signs of recent activity. For now, Olympus Mons remains a frozen monument to an era when the red planet’s interior ran hot and its volcanoes reshaped the world.
Studying a giant from orbit and the ground
Because Olympus Mons is so broad and so gently sloped, its full shape is far easier to appreciate from space than from its surface, and much of what is known comes from spacecraft that have mapped Mars in fine detail from orbit. Laser altimeters have measured its height and profile, while high-resolution cameras have traced individual lava flows, wrinkles, and channels down its flanks. Landers and rovers elsewhere on Mars have measured seismic rumbles from the planet’s interior, adding to the picture of how heat still moves beneath the surface. Each new mission refines the understanding of when the volcano last erupted and whether the deep Martian interior retains any of the warmth that once fed such an extraordinary peak.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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