Mountains are cold, windy places where only certain animals can survive – including agile hunters such as pumas and snow leopards, and nimble grazers such as mountain goats, yaks, ibex and chamois.
The world’s highest-living mammal is the yak, a type of wild cattle which can survive more than 6,000 m up in the Himalayas of Tibet.
Mountain goats have hooves wit that dig into cracks in the rock, and that act like suction pads.
In winter, the mountain goat’s pelage (coat) turns white, making it hard to spot against the snow.
The Himalayan snowcock nests higher than almost any other bird – often above 4,000 m in the Himalayas.
The Alpine chough has been seen flying at 8,200 m up on Everest.
Lammergeiers are the vultures of the African and southern European mountains. They break tough bones by dropping them from a great height onto stones and then eating the marrow.
The Andean condor of the South American Andes is a gigantic scavenger which can carry off deer and sheep. It is said to dive from the skies like a fighter plane.
The puma, or mountain lion, can jump well over 5 m up onto a rock ledge – that is like you jumping into an upstairs window.
The snow leopard of the Himalayan Mountains is now one of the rarest of all the big cats, because it has been hunted almost to extinction for its beautiful fur coat.
Conditions get colder, windier and wetter higher up mountains, so plants get smaller and hardier.
On lower slopes conifers such as pines, firs, spruces and larches often grow.
Above a certain height, called the tree-line, it gets too cold for trees to grow.
In Australia, eucalyptus trees grow near the tree-line. In New Zealand, Chile and Argentina southern beeches grow.
Above the tree-line stunted shrubs, grasses and tiny flowers grow. This is called alpine vegetation.
Alpine flowers like purple and starry saxifrage have tough roots that grow into crevices and split the rocks.
There are few insects high up, so flowers like saxifrage and snow gentian have big blooms to attract them.
To make the most of the short summers, the alpine snowbell grows its flower buds the previous summer, then lets the bud lie dormant through winter under snow.
Alpine flowers such as edelweiss have woolly hairs to keep out the cold. Tasmanian daisies grow in dense cushion-shapes to keep warm.
As you go higher up a mountain, the trees of the lower slopes thin out. At the top, only mosses and lichens grow.
On Mt Kenya in Africa, huge dandelion-like plants called giant groundsels grow as big as trees.
Great mountain ranges such as the Andes in South America usually lie along the edges of continents.
Most mountain ranges are made by the folding of rock layers as tectonic plates move slowly together.
High ranges are geologically young because they are soon worn down. The Himalayas are 25 million years old.
Many ranges are still growing. The Himalayas grow a few centimeters each year as the Indian plate pushes into Asia.
Mountain-building is slow because rocks flow like thick treacle. Rock is pushed up like a bow wave in front of a boat as one tectonic plate pushes into another.
Satellite techniques show that the central peaks of the Andes and Himalayas are rising. The outer peaks are sinking as the rock flows slowly away from the ‘bow wave’.
Mountain-building is very active during orogenic (mountain-forming) phases that last millions of years.
Different orogenic phases occur in different places, for example the Alpine, Caledonian, Hercynian in Europe and the Huronian, Nevadian and Pasadenian in North America. The Caledonian was about 550 million years ago.
Mountain-building makes the Earth’s crust especially thick under mountains, giving them very deep ‘roots’.
As mountains are worn down, their weight reduces and the ‘roots’ float upwards. This is called isostasy.
A few high mountains are lone volcanoes, such as Africa’s Kilimanjaro, which are built by many eruptions.
Some volcanic mountains are in chains in volcanic arcs (see volcano zones), such as Japan’s Fujiyama.
Most high mountains are part of great mountain ranges stretching over hundreds of kilometers.
Some mountain ranges are huge slabs of rock called fault blocks. They were forced up by quakes.
The biggest mountain ranges, such as the Himalayas and the Andes, are fold mountain ranges.
The height of mountains used to be measured from the ground, using levels and sighting devices to measure angles. Now mountains are measured more accurately using satellite techniques.
Satellite measurements in 1999 raised the height of the world’s highest peak, Mt Everest in Nepal in the Himalayas, from 8848 m to 8850 m.
All 14 of the world’s peaks over 8000 m are in the Himalayas — in Nepal, China and Kashmir.
Temperatures drop 0.6°C for every 100 m you climb, so mountain peaks are very cold and often covered in snow.
The air is thinner on mountains, so the air pressure is lower. Climbers may need oxygen masks to breathe.