Olympus Mons towers 21 kilometers above the Martian surface—roughly 2.5 times the height of Mount Everest. That’s not a volcano. That’s a monument to what happens when you remove plate tectonics from the equation.
When Planets Forget How to Move Their Crusts Around
Earth’s volcanoes are restless wanderers. They erupt, build up, then get carried away on tectonic plates like passengers on the world’s slowest conveyor belt. Hawaii’s Mauna Kea formed over a stationary hotspot, but the Pacific Plate kept moving, creating a chain of islands stretching 6,000 kilometers across the ocean. Each island is a timestamp—a geological breadcrumb trail showing where the plate used to be.
Mars? Mars said no thanks to all that movement.
The Red Planet’s crust just sits there, frozen in place like a student who showed up to class but refuses to participate. When a hotspot develops underneath, magma keeps piling onto the same spot for billions of years. Olympus Mons isn’t just big because Martians wanted bragging rights—it’s big because it had roughly 3 billion years to grow without anyone moving the damn plate.
Here’s the thing: Earth’s largest volcano, Mauna Loa in Hawaii, manages a respectable 4,169 meters above sea level (though it’s actually about 9,000 meters from its base on the ocean floor). It last erupted in 2022, reminding everyone that it’s very much still active. But compare that to Olympus Mons—600 kilometers wide at its base, with cliffs rising 8 kilometers high around its perimeter. The caldera alone spans 80 kilometers across, large enough to swallow Los Angeles whole.
Turns out size matters when you’re talking about volcanic shields.
The Atmosphere That Couldn’t and the Gravity That Wouldn’t
Martian gravity is about 38% of Earth’s—a detail that sounds minor until you realize what it means for volcanic eruptions. Lower gravity means lava fountains can shoot higher, ash plumes can billow farther, and eruption columns can reach altitudes that would be physically impossible on Earth. A 1979 study comparing theoretical eruption dynamics suggested Martian volcanic plumes could reach 100 kilometers high compared to Earth’s maximum of around 45 kilometers during super-eruptions like Tambora in 1815.
Then there’s the atmosfere situation.
Mars has basically no atmosphere—about 0.6% of Earth’s atmospheric pressure at sea level. This means Martian lava doesn’t have to fight through thick air resistance. It flows faster, farther, creating those massive shield structures with gentle slopes averaging just 5 degrees. Earth’s shield volcanoes, like those in Iceland or Hawaii, typically have slopes between 5-10 degrees because our thicker atmosphere and higher gravity constrain how far lava can spread before it cools and solidifies.
Wait—maybe the weirdest difference isn’t size or atmosphere but timeline. Earth’s most active volcanic regions are young, geologically speaking. Mount St. Helens began forming roughly 40,000 years ago. Kilauea in Hawaii is between 210,000 and 280,000 years old. These are babies.
Martian volcanoes are geologically active—or were until relatively recently. Some lava flows on Olympus Mons may be as young as 2 million years old, which in geological terms is practically yesterday. But the structures themselves formed over timescales that make Earth’s volcanoes look like mayflies. The Tharsis Montes region, which includes Olympus Mons and three other massive shield volcanoes, began forming around 3.7 billion years ago during the Noachian period.
That’s older than most of Earth’s continental crust.
The Tharsis bulge—the massive volcanic plateau that dominates Mars’s western hemisphere—is so heavy it actually changed the planet’s axial tilt over time. An entire volcanic region so massive it tilted the planet. Earth’s volcanism builds mountains and creates islands, sure, but it doesn’t fundamentally alter the planet’s rotation. Mars went all-in on volcanism and ended up redecorating its entire orbital geometry.
Nobody asked for that level of commitment.
