OLYMPUS MONS - Largest Volcano in Solar System

The largest known volcano in our solar system OLYMPUS MONS on the planet Mars. At a height of almost 22 km it is roughly three times as tall as Mount Everest and is the also tallest known mountain in the Solar System.. Olympus Mons had been known to astronomers since the late 19th century as the albedo feature Nix Olympica.

Olympus Mons is the youngest of the large volcanoes on Mars, having formed during Mars' Amazonian Period.  Olympus Mons is the result of many thousands of highly fluid, basaltic lava flows that poured from volcanic vents over a long period of time.
The extraordinary size of Olympus Mons is likely because Mars lacks mobile tectonic plates. Unlike on Earth, the crust of Mars remains fixed over a stationary hotspot, and a volcano can continue to discharge lava until it reaches an enormous height.