Compared to a hill, a mountain is defined by its greater height and volume. A plateau is distinguished by its flat surface and a mountain by its greatly irregular surface. Most mountains are peaked, but many have flat tops. Altimetry is the measurement of altitude, or elevation above sea level. Mountain altitudes can be measured by an aneroid barometer designed to register changes in atmospheric pressure accompanying changes in altitude, by radar altimetry, or by the traditional triangulation survey of points of known altitudes.
Modern satellites make it possible to determine the elevation of any remote peak on Earth.
Subsea mountains, usually volcanic cones, are commonly associated with midoceanic ridges or hot spots in the Earth. The massive volcano Mauna Loa, on the island of Hawaii, is one of the largest mountains in the world. Mountains have played a major role in human history, forming geopolitical boundaries between countries and natural barriers to migration and transportation. They also have formed refuge areas for distinctive mountain cultures and economies such as those that have flourished in the Himalayan nations of Tibet and Nepal. Potential waterpower and mineral deposits are commonly found in mountains but are frequently expensive to develop.