What volcano, with a height of nearly 22 km, is the reason scientist believe that the location of the poles of Mars have shifted?
True polar wander on Mars: For some time, scientists have thought that the location of the poles of Mars have shifted due to the great mass of volcanic material in the Tharsis dome which includes Olympus Mons, the highest volcano in the solar system. Olympus Mons:  By one measure, it has a height of nearly 22 km (13.6 mi or 72,000 ft).
Olympus Mons