Olympus Mons on Mars towers nearly three times higher than Everest

Standing at the base of Mount Everest and looking up accounts for one of the more humbling views available on Earth, yet the tallest mountain in the solar system would make Everest look like a foothill by comparison. That mountain, Olympus Mons, sits on Mars rather than on any world humans have walked, and its scale only becomes clear once its height, width, and shape are compared directly against the volcanoes and mountains familiar from home. Understanding why Mars grew a volcano this large, and Earth never did, comes down to a difference in how the two planets’ surfaces behave over hundreds of millions of years.

A Summit Nearly Three Times Higher Than Everest

Olympus Mons rises roughly 22 kilometers, or about 13.6 miles, above the surrounding Martian plains, and NASA’s own reference materials put its total relief closer to 25 kilometers once the surrounding scarp is included, figures that consistently work out to somewhere near three times the height of Mount Everest above sea level. The volcano’s footprint is just as extreme as its height, spanning roughly 624 kilometers, or about 374 miles, across, an area comparable in size to the state of Arizona. That combination of extreme height packed into an extremely broad base is what makes Olympus Mons the largest known volcano in the solar system, not just the tallest mountain on Mars specifically.

Why It Is Called a Shield Volcano

Olympus Mons owes its shape to how it formed rather than to any single dramatic eruption. NASA’s own Mars atlas classifies it as a shield volcano, a type built up gradually as highly fluid, low-viscosity lava flows spread out over the surface and cool in place, layer after layer, rather than erupting violently and piling up steep-sided cones the way a stratovolcano does. That gentle, gradually widening profile is why the slopes of Olympus Mons rise only a few degrees at any given point despite the mountain’s overall height, a shape that would look almost flat from ground level even though it towers over everything around it from a distance. Hawaii’s Mauna Loa is the closest terrestrial comparison in shape and formation, though Olympus Mons dwarfs it by more than an order of magnitude in total volume.

The Collapsed Caldera at the Summit

At the top of Olympus Mons sits a summit caldera roughly 80 kilometers, or about 50 miles, across, formed not by a single crater but by several overlapping collapse pits that developed as underlying magma chambers drained and their roofs caved in over time. Detailed elevation mapping of that caldera floor has found more than a kilometer of vertical change across its surface, evidence that the floor itself formed in stages as a series of lava lakes rose, drained, and collapsed again rather than settling all at once. NASA’s Astronomy Picture of the Day archive has repeatedly featured orbital imagery of the caldera, which shows the nested, overlapping pits clearly enough to trace the volcano’s layered eruptive history from orbit alone.

A Mountain Mars Could Grow That Earth Never Could

The reason Mars has a mountain this size and Earth does not comes down to plate tectonics, or rather the lack of it on Mars. On Earth, the crust is broken into moving plates, so a hot spot of rising magma beneath the surface only stays under any one point briefly before the plate drifts onward, which is why Hawaii is a chain of many separate volcanic islands rather than a single towering peak. Mars has no moving plates, so its crust has stayed fixed in place over the same mantle hot spot for hundreds of millions, if not billions, of years, letting lava from that single source pile up on the same spot indefinitely instead of getting spread across a trail of smaller volcanoes.

A Volcano That Formed Early and Stopped Recently, Geologically Speaking

Age estimates place Olympus Mons among the oldest of Mars’s giant shield volcanoes, with construction beginning billions of years ago even as some of its surface lava flows appear to be only tens of millions of years old, young enough in geological terms that scientists have not ruled out the possibility that the volcano could still be capable of erupting again someday. That combination of ancient origins and comparatively recent activity makes Olympus Mons a rare window into a magma system that may have stayed active, on and off, for longer than almost any volcanic feature known on Earth, all because the ground beneath it never had anywhere else to go.

How Orbiting Instruments Measured a Mountain No One Could Climb

Getting an exact height and width for a mountain this large required tools no ground-based survey could ever provide. Much of the precise elevation data now cited for Olympus Mons comes from laser altimetry carried aboard NASA orbiters, instruments that fire a laser pulse toward the surface and time how long the reflection takes to return, building up a highly detailed map of elevation across the entire volcano from orbit rather than from anyone standing on its slopes. That kind of survey is what allows scientists to say with confidence that the caldera floor varies by more than a kilometer in height, or that the surrounding basal scarp adds several kilometers to the volcano’s total relief beyond its main slope, details no single photograph alone could resolve. Follow-up imaging from later orbiters sharp enough to pick out boulders and individual lava-flow edges has let researchers refine the age estimates for different sections of the volcano’s surface, comparing how many small craters have accumulated on one flow versus another to work out roughly when each layer of lava cooled.

This article was produced with the assistance of AI and reviewed by Morning Overview editors.

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