The tallest volcano in the solar system.
Olympus Mons is the largest volcano — and the highest mountain — in the entire solar system. It rises 21.9 km (13.6 miles) above the Martian plains and spans roughly 600 km across, sitting on the Tharsis volcanic bulge near the Martian equator.
Claim your plot here →Why is Olympus Mons so absurdly big? Because Mars has no moving tectonic plates. On Earth, a volcanic hotspot drifts under shifting crust and spreads its eruptions into a chain of islands — that is how Hawaii formed. On Mars the crust stays put, so the same hotspot pumps lava into a single spot for billions of years. The result is one colossal mountain instead of a scattered chain.
Its slopes are so gentle (about 5°) and its base so vast that if you stood on the summit, the edge of the volcano would curve away below the horizon — you literally could not see where it ends.
About 2.5× taller — Everest tops out at 8.8 km, Olympus Mons reaches 21.9 km.
Its base is roughly 600 km wide — wide enough to blanket the whole of France, or the state of Arizona.
The summit rises above 99% of the thin Martian atmosphere — for all practical purposes, in space.