Earth's longest mountain chain runs 65,000 kilometres, almost entirely underwater
The Andes stretch about 7,000 kilometres and are often called the longest mountain system on land. Count the submerged Ocean Ridge, though, and you get a continuous chain of peaks around 65,000 kilometres long, winding across the sea floor where almost nobody will ever see it.
A mountain range is a line of peaks or hills joined by high ground, usually broken up by passes and valleys. Several ranges that share a shape, structure and alignment, and that grew from the same mountain-building episode, make up a larger system or belt. Most of the important ones on our planet owe their existence to plate tectonics. Neighbouring summits need not be built alike, though: one range can mix thrust sheets, raised blocks, folded strata and volcanoes, and so contain many kinds of rock.
Nearly all of the young ranges on land belong to two great belts. The Pacific Ring of Fire takes in the Andes, the North American Cordillera, Japan and the Philippines, reaching down to New Zealand. The Alpide belt runs roughly 15,000 kilometres from Java to Iberia, taking in the Alps and the Himalayas, home of Everest at 8,848 metres. Plenty of ranges sit outside both, among them the Appalachians and the Western Ghats.
Ranges also steer the weather. Air pushed up a slope cools and drops rain or snow; once over the crest it sinks, warms and arrives dry, leaving a rain shadow on the far side. Big ranges such as the Andes therefore split continents into separate climate zones.
Erosion attacks a range even while it is rising. As the Colorado Rockies lifted in the early Cenozoic, around 3,000 metres of mostly Mesozoic sedimentary rock was stripped off their core and spread as sand and clay over the Great Plains, and losing that weight probably let the range rise further. Rivers are usually credited with most of the wearing down, but simulations suggest erosion slows once a belt goes tectonically quiet, since fewer landslides and less grit reach the water. Other worlds have ranges too: Maxwell Montes on Venus outtops anything on Earth, while the chains on Pluto and Titan are made largely of ice.
Source: Mountain range
