What is the name of the Martian volcano with a height of about 21.9 km?

Olympus Mons is the Martian volcano with a height of about 21.9 kilometers. It rises roughly 21.9 kilometers above Mars’s reference surface and is the tallest known volcano and planetary mountain in the Solar System by that measurement.

Olympus Mons is a shield volcano, built by many eruptions of relatively fluid basaltic lava. Its broad, gently sloping sides differ from the steep cone of a classic composite volcano. The volcano is about 600 kilometers across, making its footprint enormous even though its average slope is surprisingly shallow.

The volcano formed in the Tharsis region, a vast volcanic plateau near Mars’s equator. Mars lacks Earth-like active plate tectonics, so a volcanic hotspot could continue building the same structure over a long period instead of producing a chain of separate volcanoes. A large summit caldera, created when the volcano’s magma chambers emptied and collapsed, caps Olympus Mons.

The other options are also major Tharsis volcanoes. Arsia Mons, Pavonis Mons, and Ascraeus Mons belong to the same regional volcanic system, but none is as tall as Olympus Mons.