Mountains and plateaus

Mountains and plateaus are the highest places on Earth's land surface. They are not random — they sit where the slow but immense forces of the planet have pushed, folded, or melted rock upward over millions of years. Understanding why a mountain range stands where it does also helps explain weather patterns, where civilizations grew, and where rivers begin.

How mountains form

Earth's outer shell is broken into huge slabs called tectonic plates. These plates drift across the planet at about the speed your fingernails grow. Where two plates push against each other (a convergent boundary), the crust is squeezed upward — this is called folding — and a mountain range rises. The Himalayas formed this way and are still rising about 5 mm per year as India grinds northward into Asia. Where one plate dives under another, magma rises and bursts out as volcanoes; the Andes contain many active volcanoes formed exactly this way.

The great mountain ranges

• Himalayas (Asia) — the tallest range on Earth, home to Mount Everest (8,849 m). Stretches across Nepal, India, Bhutan, and Tibet.
• Andes (South America) — the longest mountain range in the world, running 7,000 km down the western edge of the continent.
• Rocky Mountains (North America) — stretching from British Columbia in Canada down through the western United States to New Mexico.
• Alps (Europe) — curving across France, Switzerland, Italy, Austria, and Slovenia.
• Atlas Mountains (Africa) — running through Morocco, Algeria, and Tunisia in the north-west of the continent.
• Ural Mountains (Europe/Asia) — the traditional dividing line between Europe and Asia.

Plateaus

A plateau is a large area of land that has been pushed up high above the surrounding country but stays relatively FLAT on top — like a giant table. The Tibetan Plateau, sitting just north of the Himalayas at an average elevation of 4,500 m, is the largest plateau on Earth and is sometimes called "the roof of the world". The Colorado Plateau in the south-western United States is famous for the Grand Canyon, which the Colorado River has cut down into it over millions of years.

Mountains and climate — the rain shadow

Mountains powerfully shape the climate of nearby regions. When wet air from an ocean blows toward a mountain range, it is forced upward, cools as it rises, and drops most of its moisture as rain or snow on the windward side. By the time the air sweeps down the other side, it is dry — creating a rain shadow. The Sierra Nevada in California catches almost all the Pacific moisture, leaving the Mojave and Great Basin deserts in its rain shadow. The same effect leaves the Patagonian desert in the rain shadow of the Andes.

Mountains and people

Mountains have always made human life difficult: thin air at high elevation, cold temperatures, steep slopes that resist farming, and barriers that block roads and armies. Yet they have also protected people — the Swiss in the Alps and the Tibetans in the Himalayas built distinctive cultures partly because mountains kept invaders out. Today mountains are important for fresh water (most great rivers begin there), tourism, mining, and renewable hydroelectric power.