The Tallest Volcano on Mars

Olympus Mons is a shield volcano on Mars. It stands 21.287 kilometres high above the surface.

Mars lacks mobile tectonic plates. Its crust stayed fixed over a stationary hotspot for millions of years.

Prolonged volcanic activity built a mountain 600 km wide. The flanks slope at only 5 percent.

Six nested calderas form a depression up to 3.2 km deep.

The outer edge forms an escarpment up to 8 km tall. Landslides make their own escarpments.

Northwestern lava flows range from 115 Mya to 2 Mya. Olympus Mons might still be quietly erupting.

Olympus Mons began forming in that ancient Martian era.

Astronomers knew this feature as Nix Olympica before Mariner 9. Space probes confirmed the mountain.