The main types of landforms are mountains, hills, plateaus, plains and valleys, together with more specific features such as canyons, volcanoes, glaciers and the valleys they carve, dunes, mesas and buttes, caves, deltas, peninsulas, islands and, beneath the sea, trenches and ridges. The clearest way to understand them is by the process that made them. Some are pushed up by movements of the Earth's crust. Some are built by volcanoes. Most are carved by rivers, ice, wind or waves, and others are built up where those forces drop what they carry. Most real landscapes are made by several of these at once.
A landform is any natural feature of the Earth's surface with a recognisable shape, from a whole mountain range to a single sand dune. Landforms are studied in geomorphology, the branch of geography and geology concerned with how the surface takes shape and changes over time.
Pushed Up by the Crust: Mountains, Plateaus and Rifts
The largest landforms come from plate tectonics. Where two continental plates collide, the crust crumples and thickens into fold mountains. The Himalaya began rising when India met Asia about 50 million years ago and is still rising today, and the Alps, Andes and Rockies also owe their height to plate collisions. Where the crust is stretched and cracks along faults, blocks of land tilt and rise to form fault-block mountains, such as California's Sierra Nevada and Wyoming's Teton Range, with steep faces on one side.
There is no single agreed height at which a hill becomes a mountain. Many geographers use a rise of about 300 m above the surrounding land, while some countries and agencies use their own thresholds. A hill is simply a lower, usually rounder rise.
When a large area is lifted without being folded, the result is a plateau, a high, relatively flat tableland. The Tibetan Plateau averages about 4,500 m above sea level over some 2.5 million km², the largest and highest in the world. The Colorado Plateau in the south-western United States has been raised about 2 km, and its rivers have cut down through it to make canyons. Where plates pull apart, a strip of land drops between parallel faults to form a rift valley. The East African Rift runs thousands of kilometres from the Red Sea towards Mozambique, and Siberia's Lake Baikal, the deepest lake in the world at about 1,640 m, fills another rift.
Built by Volcanoes
Volcanoes build their own landforms from lava and ash. Stratovolcanoes, such as Mount Fuji at 3,776 m, are steep cones of alternating ash and sticky lava, and they erupt explosively. Shield volcanoes, such as those of Hawaii, are broad and gently sloping, built by runny basalt lava. Mauna Kea rises about 4,200 m above sea level but more than 10,000 m from its base on the sea floor, taller than Everest measured that way. When a volcano empties its magma chamber in a huge eruption and collapses, it leaves a caldera, like the one that holds Oregon's Crater Lake, explained in our guide to what a caldera is. The largest volcanic landforms of all are lava plateaus, built by floods of lava pouring from fissures. India's Deccan Traps, erupted about 66 million years ago, still cover about half a million square kilometres.
Carved by Rivers: Valleys, Canyons and Gorges
Running water is the most widespread sculptor of land. A river cutting down through rock carves a V-shaped valley, the typical shape of young river valleys in hills and mountains. Where it cuts faster than the sides can wear back, often because the land is rising or the rock is hard and dry, it makes a canyon or gorge with near-vertical walls. The Colorado River's Grand Canyon is about 446 km long and up to about 1,800 m deep.
On gentler ground, rivers wander across their floodplains in loops called meanders. When a flood cuts through the narrow neck of a loop, the old bend is left behind as a curved oxbow lake. Where rivers cross a band of hard rock onto softer rock, waterfalls form. Niagara Falls has worn its way back about 11 km since the end of the last ice age. In deserts, rivers that flow only after storms carve dry channels called wadis.
Carved by Ice
Glaciers reshape valleys in their own way. A glacier grinding down a river valley widens and deepens it into a U-shaped valley with a flat floor and steep sides. Where such a valley reaches the sea and floods, it becomes a fjord, explained in our guide to what a fjord is. At the head of a glacier, ice scoops out an armchair-shaped hollow called a cirque, often holding a small lake. Where cirques cut back into a mountain from several sides, they leave a sharp pyramidal peak, a horn, such as the Matterhorn, at 4,478 m, and knife-edged ridges called arêtes.
Glaciers also leave things behind. Moraines are ridges of rock and gravel dumped at a glacier's edges and snout. Drumlins are smooth, egg-shaped hills shaped under moving ice, and eskers are long winding ridges of gravel left by rivers that once flowed in tunnels beneath the ice. The Great Lakes of North America fill basins scoured and dammed by the ice sheets of the last glaciation.
Shaped by Wind: Dunes, Mesas and Buttes
In deserts, wind moves sand into dunes, which come in shapes that depend on the wind pattern. Crescent-shaped barchans form under steady winds from one direction, long linear dunes form where winds alternate, and tall star dunes form where winds come from many directions. Some dunes in the Namib Desert rise more than 300 m. Wind-blown sand also scours rock into strange shapes, though water still does most of the carving even in deserts.
Erosion of flat-lying rock layers in dry country leaves a sequence of flat-topped landforms. A mesa is a broad hill with a flat top and steep sides, capped by a hard layer of rock. As its edges erode it shrinks into a butte, taller than it is wide, and finally a slender pinnacle or spire. Monument Valley, on the Arizona–Utah border, shows every stage.
Shaped by the Sea
Waves attack coasts most strongly at headlands, and the results are some of the most dramatic landforms. Cliffs form where waves undercut rock. The chalk White Cliffs of Dover rise to about 110 m. Waves exploit cracks to carve caves, which can break through a headland to form a sea arch. When the arch collapses, it leaves an isolated sea stack, like the Twelve Apostles off Australia's Great Ocean Road, one of which collapsed into the sea in 2005.
Where currents carry sand along a coast, they build beaches, long spits reaching out into open water, and barrier islands such as North Carolina's Outer Banks. A tombolo is a sand bar that joins an island to the mainland. Larger coastal landforms include peninsulas, land almost surrounded by water, capes, bays and gulfs.
Built Up Where Sediment Settles: Plains, Deltas and Fans
Everything eroded from mountains has to go somewhere, and where it settles it builds new land. Large plains are often made of sediment laid down by rivers. The Indo-Gangetic Plain of northern India, built by rivers from the Himalaya, is one of the most fertile and densely populated regions on Earth. Where a river meets the sea and drops its load, it builds a delta, described in our explainer on what a delta is. Where a steep mountain stream reaches flat ground in a dry region, it spreads its gravel in an alluvial fan, like those lining the mountain fronts of Death Valley.
Dissolved From Below: Caves and Karst
Where the bedrock is limestone, rain and groundwater, made slightly acidic by carbon dioxide, dissolve the rock. The result is karst: sinkholes, disappearing streams, underground rivers and caves. Vietnam's Son Doong, explored in 2009, has one of the largest known cave passages, big enough to hold a city block with its own jungle. In southern China, around Guilin, karst has produced steep limestone towers rising from flat plains. The name comes from the Kras plateau on the Slovenian–Italian border.
Islands, Atolls and the Hidden Landforms of the Sea Floor
Islands form in many ways: as volcanoes rising from the sea floor, as pieces of continents cut off by rising seas, or as sand and coral built up on shallow banks. An atoll is a ring of coral reef and islets around a lagoon. In 1842 Charles Darwin proposed that atolls form as coral keeps growing upward around a volcanic island that slowly sinks. His idea was confirmed in 1952, when drilling on Enewetak Atoll reached volcanic rock beneath about 1,300 m of coral.
Most of the Earth's relief is actually underwater. The mid-ocean ridge, a volcanic mountain range about 65,000 km long, winds through every ocean. Trenches, where one plate sinks beneath another, reach almost 11 km deep in the Mariana Trench. Flat abyssal plains cover much of the deep ocean floor, dotted with thousands of seamounts, extinct undersea volcanoes. If the oceans were drained, these would be the largest landforms on the planet.