A mountain is defined as a landform that rises prominently above its surroundings, typically exhibiting steep slopes and a limited summit area. Mountains generally possess considerable local relief, meaning a significant difference in elevation between the peak and the surrounding base land. Many definitions require a minimum elevation, such as rising at least 600 meters (about 2,000 feet) above the adjacent terrain. These geological structures are a product of large-scale planetary processes shaping Earth’s surface.
Major Continental Mountain Ranges
The largest mountain systems on Earth are found across the continents, forming vast, elongated belts known as cordilleras or orogenic belts. One of the most geographically expansive systems is the American Cordillera, which runs nearly continuously along the western edge of the Americas. This immense chain begins with the Rocky Mountains, stretching approximately 4,800 kilometers (3,000 miles) from British Columbia down to New Mexico.
The cordillera continues southward as the Andes, the world’s longest continental mountain range, extending for about 7,000 kilometers (4,350 miles) along the Pacific coast of South America. The Andes span seven countries, from Venezuela down through Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina. This narrow, high-altitude range includes Mount Aconcagua, the tallest peak outside of Asia, and is characterized by numerous active volcanoes.
In the Eastern Hemisphere, the Alpine-Himalayan orogenic belt represents another major concentration of terrestrial mountains. The Himalayas, which contain the planet’s highest peaks, extend for over 2,400 kilometers (1,500 miles) across southern Asia. This range spans five nations, including India, Nepal, Bhutan, China (Tibet), and Pakistan, forming a massive natural barrier.
The European Alps are part of this same geological belt, stretching for about 1,200 kilometers (750 miles) across eight countries, including France, Switzerland, and Italy. Other significant continental ranges include the Atlas Mountains (2,500 km across North Africa) and the Great Dividing Range (3,500 km along the eastern coast of Australia). The Transantarctic Mountains form a range of roughly 3,500 kilometers, dividing Antarctica into East and West Antarctica.
Mountains of the Ocean Floor and Other Worlds
The longest mountain chain on the planet is hidden beneath the oceans. The Mid-Ocean Ridge (MOR) system is a continuous, volcanic mountain range that wraps around the globe. This extensive system measures between 65,000 and 80,000 kilometers (40,000 to 50,000 miles) in length, making it the longest mountain range in the world.
The MOR system lies deep underwater, with its crest typically sitting about 2,500 meters (8,200 feet) below the ocean surface. Peaks along the ridge often rise approximately 2,000 meters above the surrounding seafloor. Sections of this immense submarine range, such as the Mid-Atlantic Ridge and the East Pacific Rise, traverse all of Earth’s major ocean basins.
Mountain-like structures exist on other celestial bodies, demonstrating that mountain formation is a widespread planetary process. On Mars, the enormous shield volcano Olympus Mons is the tallest known planetary mountain in the Solar System, towering approximately 21.9 kilometers (13.6 miles) above the Martian datum. This height is about 2.5 times the elevation of Mount Everest above sea level.
The Moon also features significant mountainous terrain, often found along the rims of large impact basins. Lunar mountains, such as the Malapert Massif near the south pole, can exhibit local relief exceeding 7,500 meters. Unlike Earth’s mountains, which form slowly through tectonic movement, many lunar mountains were created instantly by the massive shockwaves from asteroid and comet impacts.
Tectonic Forces Determining Mountain Location
The locations of Earth’s mountain ranges are determined by the dynamics of plate tectonics, particularly the interactions at plate boundaries. Mountains are concentrated where lithospheric plates converge, diverge, or where extensional forces cause faulting. The planet’s highest mountains form at continental collision zones, which are a type of convergent boundary.
When two continental plates collide, neither is dense enough to subduct fully into the mantle. Instead, the immense compressive forces cause the crust to crumple, thicken, and fold, pushing rock upward to form massive, non-volcanic mountain ranges. The Himalayas are the most prominent example of this mechanism, created by the ongoing collision between the Indian and Eurasian plates.
Subduction zones are another common mountain-building mechanism, occurring where denser oceanic crust slides beneath a continental or less dense oceanic plate. The friction and heat cause the subducting plate to release fluids that melt the overlying mantle, leading to volcanism on the upper plate. This process creates continental volcanic arcs, such as the Andes in South America, or volcanic island arcs like the Aleutian Islands.
Mountain formation also happens at divergent boundaries, where plates move apart. The Mid-Ocean Ridge system is formed by this seafloor spreading, as magma rises to fill the gap and solidify into new oceanic crust. On continents, extensional forces can cause the crust to stretch and fracture, forming fault-block mountains where large segments are uplifted relative to subsided blocks, exemplified by ranges like the Sierra Nevada.