What is the largest volcano in the solar system?

Olympus Mons is the largest volcano in the Solar System. This enormous shield volcano rises on Mars and is far larger than any volcano on Earth.

Olympus Mons formed from repeated eruptions of relatively fluid basaltic lava. Mars lacks Earth's active plate-tectonic recycling, so a volcanic hotspot could remain beneath one region for a very long time, allowing layer after layer of lava to accumulate. The result is a broad, gently sloping mountain rather than a steep cone.

The volcano stands about 22 kilometres above the surrounding Martian plains, although measurements vary depending on the reference level used. Its summit contains a complex group of overlapping calderas formed when magma chambers emptied and collapsed.

Olympus Mons is often described as the tallest mountain in the Solar System, though comparisons depend on how height is measured. Earth's Mauna Loa is the largest terrestrial volcano by volume, while Tamu Massif is a remarkable seafloor volcano; neither approaches Olympus Mons in overall scale.