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The World's Great Mountain Ranges
Mountains look like the one permanent thing on the map, the part you could set your watch by. They are not. The Himalaya is still growing, pushed a little higher most years, and the Appalachians were once as sharp as the Alps before a few hundred million years wore them down to green stubs. A mountain range is a slow-motion collision, frozen mid-crash.
How ranges are born
Most great ranges are the work of plate tectonics. Where two continental plates grind into each other, the crust has nowhere to go but up: the Himalaya rose, and still rises, from India driving into Asia. Where an ocean plate dives beneath a continent, it buckles the edge upward and feeds it with volcanoes, which is the story of the Andes. Elsewhere, faulting tilts whole blocks of crust toward the sky, as it did with the Sierra Nevada. Each mechanism leaves a signature you can learn to spot.
Young and sharp, old and soft
A range wears its age in its silhouette. Young mountains are tall and jagged because erosion has not caught up with them yet, which is why the Himalaya, the Alps, and the Andes look so dramatic. Old mountains are low and rounded because water and ice have been filing them down for ages, which is why the Appalachians and the Urals roll rather than jab. Height and sharpness are a rough clock.
The record holders
The Himalaya holds the highest peaks on Earth, crowned by Mount Everest at about 8,849 metres above sea level. The Andes is the longest mountain range above water, running some 7,000 kilometres down the western spine of South America. The single longest mountain chain of all is actually the mid-ocean ridge, a volcanic seam that circles the globe, but it stays hidden beneath the sea.
Reading a mountain range in a clue
Altitude, thin air, and words like "young" or "ancient" all place you. A high, sharp, still-rising range points to a collision zone; a low, worn, rounded one points to a range long past its prime. Pair a range with a hemisphere or a nearby coastline and you have narrowed the whole world down to a single ribbon of high ground.
Bottom Line
Mountains rise where the crust is squeezed, most often at colliding plate boundaries, over spans of time that make the map look frozen. The Himalaya is young and highest, the Andes is longest on land, and old ranges like the Appalachians have been smoothed by erosion. Read the height and the shape and the range tells you roughly where, and roughly when.
Frequently Asked Questions
How do mountain ranges form?
Most form through plate tectonics, when colliding plates push the Earth's crust upward or one plate dives beneath another. Over millions of years this slow collision raises ranges like the Himalaya and the Andes.
What is the longest mountain range in the world?
The longest range above sea level is the Andes, stretching about 7,000 kilometres along western South America. The longest overall is the mid-ocean ridge, a volcanic chain that runs underwater around the globe.
What is the highest mountain range?
The Himalaya has the highest peaks on Earth, including Mount Everest at roughly 8,849 metres above sea level. It formed, and is still rising, from the collision of the Indian and Eurasian plates.
Why are some mountains jagged and others rounded?
Jagged mountains are geologically young, so erosion has not yet worn them down, as with the Alps and Himalaya. Rounded mountains like the Appalachians are very old and have been smoothed by hundreds of millions of years of weathering.