Which volcano is the highest mountain in the solar system, rising on Mars?

Olympus Mons is the highest mountain in the Solar System. This enormous shield volcano stands on Mars and rises about 21.9 kilometres above the surrounding plains, making it nearly two and a half times the height of Mount Everest when measured from sea level on Earth.

Olympus Mons formed from repeated eruptions of fluid basaltic lava. Mars has lower gravity than Earth and lacks the active plate-tectonic recycling that would move a volcanic hotspot away from one location. As a result, lava could accumulate over a very long period to produce an exceptionally broad volcano. Its gentle slopes extend across an area comparable to a large terrestrial country.

The volcano sits in the Tharsis region, a vast volcanic plateau containing several other giant mountains. Its summit includes a complex caldera made from overlapping collapse depressions. Spacecraft observations show lava flows of different ages, indicating that Olympus Mons was active over extended geological timescales, although it is not known to be erupting today.