The tallest mountain on Earth would look almost modest next to the giant that rises from the plains of Mars. Olympus Mons, a sprawling volcano in the planet’s western hemisphere, climbs to a height that dwarfs Mount Everest and stretches across an area roughly the size of a large U.S. state. It is the tallest volcano in the solar system, and its scale says as much about how Mars is built as it does about the mountain itself.
Measured from its base, Olympus Mons reaches an elevation somewhere in the range of 22 kilometers, with some references putting the figure closer to 26 kilometers when the surrounding terrain is taken into account. Mount Everest, by comparison, tops out at about 8.85 kilometers above sea level. That puts the Martian volcano at roughly two and a half to three times the height of the highest point on Earth, depending on where the measurement begins.
A shield volcano the size of a country
Olympus Mons is not a steep, jagged peak. It is a shield volcano, built up over long stretches of time by runny lava that flowed out and spread across the surface rather than erupting explosively. According to Britannica’s overview of the volcano, the central edifice rises about 22 kilometers high and stretches roughly 700 kilometers across, giving the whole structure a low, broad profile with an average slope of only about 5 percent. A hiker standing on its flank might not even register that the ground was tilted.
The footprint is difficult to grasp. Laid over the United States, Olympus Mons would blanket the entire state of Arizona; set down on Europe, it would cover most of France. It holds on the order of a million cubic miles of volcanic material, a volume about a hundred times greater than Mauna Loa, the largest single volcano on Earth. A steep cliff, or escarpment, several kilometers tall rings much of its outer edge, dropping abruptly to the plains below.
Why Mars could grow a mountain this big
A volcano of this size could not exist on Earth, and the reason comes down to how the two planets are put together. Earth’s crust is broken into tectonic plates that slide slowly over hot spots in the mantle. Hawaii’s volcanic chain formed because the Pacific plate kept moving, so no single volcano sat over the rising plume long enough to grow without limit. Mars appears to lack that kind of active plate movement. A volcano there can park over a magma source for hundreds of millions of years and simply keep stacking lava on the same spot.
Lower surface gravity helps as well. Mars pulls on rock with roughly 38 percent of Earth’s gravitational strength, which means a towering pile of volcanic material is less likely to collapse under its own weight. As Space.com notes in its profile of the mountain, that combination of a stationary crust and weaker gravity let Olympus Mons rise far higher than any peak the more restless Earth can sustain.
The caldera at the summit
At the top of Olympus Mons sits a complex of collapsed craters known as a caldera, formed when underground magma chambers emptied and the roof above them fell in. The summit depression spans roughly 80 kilometers and contains several overlapping pits at different depths, evidence that the volcano erupted and subsided in more than one episode over its long life. Studying those nested craters gives planetary scientists a way to read the sequence of eruptions much like counting the rings of a tree.
Age estimates based on crater counts suggest some of the lava flows on the volcano’s flanks are relatively young in geological terms, with the most recent activity possibly occurring within the last few tens of millions of years. That does not mean an eruption is imminent, but it leaves open the question of whether Olympus Mons is truly extinct or merely dormant.
What the mountain reveals about Martian history
Olympus Mons sits at the edge of the Tharsis region, a vast volcanic plateau that also hosts several other enormous volcanoes. The sheer bulk of material piled up across Tharsis has influenced the whole planet, and some researchers have argued it was heavy enough to affect the tilt and balance of Mars over geological time. Mapping these features is a central part of the ongoing exploration effort documented by NASA’s Mars program, which uses orbiters and landers to chart the planet’s surface in detail.
Understanding how Mars grew a mountain nearly three times the height of Everest also feeds back into questions about the planet’s interior. The size and structure of Olympus Mons imply a thick, rigid outer layer capable of supporting the load, along with a long history of volcanic heat rising from below. Those conditions shaped the atmosphere, the surface chemistry, and possibly the prospects for water and habitability in the distant past.
For now, the volcano stands as a marker of just how different two rocky neighbors can be. Earth constantly recycles its crust and rarely lets any single peak grow unchecked. Mars, quieter and lighter, held still long enough for one volcano to climb toward the sky and stay there, a monument built from countless slow flows of lava over an almost unimaginable span of time.
This article was researched and drafted with the assistance of AI and reviewed before publication.
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