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A mountain is a steep-sided mass of rock, rising at least 600 m (2,000 ft)

above sea level. Mountains are found on land and under the sea. Some are

isolated peaks, but most are found in a. RANGE.

WHERE IS THE WORLD’S LONGEST MOUNTAIN CHAIN?

The longest mountain chain on land is the Andes, which runs for 7,200 km

(4,470 miles) down the western edge of South America. An undersea mountain

chain called the Mid-Atlantic Ridge is even longer. It stretches 11,300 km

(7,000 miles) down the centre of the Atlantic Ocean.

WHY ARE MANY MOUNTAINS SNOW-CAPPED?

Mountaintops are cold because the thin air high up

does not hold the Sun’s heat well, and the temperature

falls 1°C (1.8°F) for every 150 m (500 ft) of height. It

is therefore cold enough to snow over high peaks

(even on the Equator) and, as the temperature rarely

rises above freezing, the snow never melts.

HOW ARE MOUNTAINS FORMED?

Mountains are formed by movements of the huge

tectonic plates that make up Earth’s crust. Fold

mountains are formed when plates collide. Block

mountains occur when a slab of land is forced

upwards. Volcanic mountains are built up from

layers of cooled and hardened lava and ash.

Most mountains are found in groups called ranges, such as the

Jura Mountains in Europe and the Sierra Nevada Mountains of

California, the United States. Often, a series of ranges is connected

in a larger chain of mountains called a cordillera.

ARE MOUNTAINS STILL

GROWING?

Some relatively young

mountains are still rising, as

colliding plates continue to force

the land at their edges upward. At

the same time, mountains are constantly

eroded by ice, rain, and the wind.

1 ANDEAN PEAKS
The Andes Mountains were formed when one of the Earth’s tectonic
plates, the Nazca plate, collided into the plate carrying South America,
slowly pushing up the rocks into a series of high, jagged peaks.

THE HIMALAYAS 3

The Himalayas are fold mountains that formed as the

plate carrying India collided with that carrying

southern Asia. These mountains are still rising, by

about 1 m (3.3 ft) every 1,000 years.

RANGES

1 MOUNTAINS AT SEA

Some of the world’s tallest

mountains lie mostly underwater,

with only their summits breaking

the surface. Mauna Kea in Hawaii

rises 10,205 m (33,480 ft) from

the ocean bed, which makes it

taller than Mount Everest.

Mountains

Cornice

are overhanging masses

of snow that build up on

ridges, blown by the wind

Mount Everest is the

world’s highest mountain,

at 8,850 m (29,035 ft)

above sea level

A fold mountain

forms where rock

is compressed,

crumpled, and

forced upwards

A rift valley forms

when a block of

land between two

faults sinks down

A block mountain forms

when a block of land between

two faults is pushed upwards

MOUNTAIN BUILDING

Faults (cracks)

occur near the

edges of plates

Mauna Kea

FIND OUT MORE. Continents 39 • Erosion 55 • Ice 58 • Rocks 46–47 • South America 232–233

mountains