Olympus Mons gets all the press—biggest volcano in the solar system, yeah yeah, we get it. But skulking just southeast of that celebrity mountain sits a trio of volcanoes that might actually tell us more about how Mars works: Ascraeus Mons, Pavonis Mons, and Arsia Mons. Together they form the Tharsis Montes, and they’re basically a geological crime scene frozen in time.
Here’s the thing about these three mountains: they’re not randomly scattered across Mars like some cosmic game of darts. They sit in an almost perfectly straight line spanning about 1,100 kilometers across the Tharsis bulge, that massive plateau rising 10 kilometers above the Martian plains. That’s higher than any mountain on Earth measured from sea level, which—let’s be honest—makes our tallest peaks look embarassingly small.
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Arsia Mons, the southernmost of the trio, stretches 435 kilometers across its base. That’s roughly the distance from Los Angeles to San Francisco, except it’s all one mountain.
The caldera at its summit plunges 110 kilometers wide—you could drop Manhattan into it sideways and still have room for Brooklyn. Scientists analyzing data from the Mars Reconnaissance Orbiter in 2017 found evidence that Arsia Mons might have erupted as recently as 50 million years ago. Which sounds ancient until you remember that Mars itself is 4.6 billion years old. In geological terms, 50 million years ago is basically yesterday afternoon.
Pavonis Mons sits smack in the middle of the three, and it’s weird. The summit sits almost exactly on Mars’s equator—within 0.5 degrees—which makes it a favorite landing site candidate for future missions, though nobody’s pulled that trigger yet. The volcano rises about 14 kilometers high, with slopes so gentle you could theoretically drive a rover straight up without tipping over. Turns out gentle slopes are the signature of shield volcanoes built from runny basaltic lava, the same stuff that built Hawaii’s Mauna Loa over millenia of patient eruptions.
Wait—maybe the strangest part is what these volcanoes tell us about Martian plate tectonics, or rather the lack thereof.
On Earth, volcanoes form chains because tectonic plates drift over hotspots in the mantle. Hawaii is the classic example: a string of islands marking where the Pacific Plate slid over a stationary plume of molten rock. But Mars doesn’t have plate tectonics. It’s crust just sits there, frozen, which means when a hotspot burns through the surface, it keeps burning in the same spot for hundreds of millions of years. That’s why Ascraeus Mons could grow to 18 kilometers high—there was no plate movement to shut off it’s magma supply or drag it away from the source.
The lava flows around these mountains are absurdly well-preserved. On Earth, wind, rain, and vegetation erase volcanic features within thousands of years. On Mars, lava flows from eruptions that happened 100 million years ago still look crisp in satellite images, their edges sharp enough to trace individual flow lobes. The Tharsis region basically stopped evolving geologically around the same time dinosaurs were having their worst day on Earth, and everything just… froze.
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The Tharsis Montes didn’t just build mountains—they likely helped destroy Mars’s magnetic field. The sheer mass of the Tharsis bulge, created by billions of years of volcanic activity, might have disrupted the planet’s mantle convection patterns. No convection means no magnetic dynamo, which means solar wind strips away the atmosphere, which means no liquid water, which means no life. Thanks, volcanoes.
Some researchers think these volcanoes could still be dormant rather than extinct. There’s no current volcanic activity detected, but with eruption cycles potentially spanning tens of millions of years, we might just be catching Mars during a very long nap. Orbital images show lava tubes and collapsed pits that could theoretically shelter future astronauts, assuming nobody minds living inside a volcano that might wake up any century now.
The weirdest detail? All three volcanoes show evidence of ancient glaciers. Ice accumulated on their flanks during Mars’s periodic climate shifts, carving out valleys and leaving behind distinctive flow patterns. Imagine: volcanoes covered in ice on a frozen desert planet that once had oceans. Mars really commits to making Earth look boring by comparison.
