The Largest Volcano in the Solar System is on Mars

Olympus Mons isn’t just big—it’s absurdly big. This Martian shield volcano is about 26 km (16 miles) high, nearly three times the height of Mount Everest. Its base covers an area as large as Arizona. Its slopes are so gentle that, standing on its flank, you might not realize you were climbing a mountain at all. The reason it got so big? Mars doesn’t have active plate tectonics like Earth, so the volcano could keep erupting in the same spot for millions of years, piling up layer after layer of rock.