Contrary to popular belief, Mount Everest is not the tallest mountain in the world. Mauna Kea in Hawaii is, with a base-to-summit height of 10,314 meters (33,480 feet) (however, its base is on the ocean floor, so its height above sea level is only 4,208 m (13,796 ft)). Mount Everest has a sea level-to-summit height of 8850 meters (29035 feet), but its base is on the Tibetan plateau, far above sea level. However, Mount Everest is the world's highest mountain. Although mountains are usually defined as the above-ground (or above-seabed) protusion from flatter land, the hard rock material of many mountains extend into the ground below them. For example, South Mountain in Phoenix, Arizona, USA, is said by geologists to be part of a series of mountain ranges 1 km high and 1 km apart created by plate collisions, which have been buried by silt, leaving only a few peaks. Through epochs they are uncovered and covered, again, repeatedly. Mount Kilimanjaro is often described as the tallest above-ground and above-water (or "free-standing") mountain in the world, measured from its base (at ground level) to the summit at 5,896 meters (19,344 feet).[/b]