The largest landform is Olympus Mons.

Olympus Mons is a shield volcano of 624 km in diameter. Olympus Mons is the size of Arizona. The entire chain of the islands on Hawaii could fit inside Olympus Mons.

Olympus Mons has 27 craters. Olympus Mons measures 342 miles across with an altitude of 69,882 feet so high it is often surrounded by clouds.

There are many volcanoes on Mars, although we have not seen any erupting. It is a question whether these volcanoes are extinct (will never erupt again), or are dormant at the present time.