What is a landform? Two kinds of forces
A landform is a natural shape on the surface of the Earth. A mountain, a valley, a plain, a beach and a cave are all landforms. A group of landforms together is a landscape.
Two sets of forces make landforms:
- Internal forces come from inside the Earth. They push, fold, crack and melt rock. They build land: mountains, volcanoes, plateaus.
- External forces come from air, water and ice: rain, rivers, waves, wind, glaciers. They wear down rock (erosion), carry the pieces (transport) and drop them somewhere new (deposition).
Building and wearing down happen together. Most changes are slow, a few millimetres each year. Some are sudden, like an eruption or a flood.
Mountains and peninsulas: the work of moving plates
The outer shell of the Earth is broken into big slabs called plates. They move very slowly, about as fast as your fingernails grow.
When two plates push towards each other, the rock between them cannot go anywhere. It crumples like a carpet pushed on the floor. The layers fold up into fold mountains, such as the Himalaya, the Alps and the Andes. These are the highest and youngest mountains. Where rock cracks and one block is lifted, we get block mountains.
A peninsula is land with sea on three sides, like the Indian peninsula, the Korean peninsula or Italy. A peninsula forms when long-lasting plate movement, uplift and the rise and fall of the sea leave a big arm of land sticking out into the sea. Its old mountains are low and rounded because rain and rivers have worn them for a very long time. Young mountains are tall and sharp.
Plateaus are high, flat lands. Some are lifted blocks of old rock. Some are made when lava spreads in thick sheets, like the Deccan plateau.
Volcanic landforms
Deep below the surface, rock melts into magma. When magma finds a crack, it rises and comes out through a vent. On the surface it is called lava. Ash, gas and lava build up around the vent into a volcano. The bowl at the top is the crater.
- Cone volcanoes have steep sides, built by layers of ash and thick lava (Mount Fuji).
- Shield volcanoes are wide and gentle, built by thin runny lava (Mauna Loa in Hawaii).
- Lava plateaus form when lava pours out of long cracks and spreads (Deccan).
Jeju Island in Korea is a volcanic island. It has a central volcano, hundreds of small cones and long tunnels called lava tubes, where lava once flowed and then drained away. Volcanoes are dangerous, yet ash and lava weather into very fertile soil, and the heat underground gives geothermal power.
River and coastal landforms: floodplains, deltas and beaches
A river changes along its journey.
- Upper course (hills): fast and steep. It cuts a deep V-shaped valley, with waterfalls and rapids.
- Middle course: the valley widens and the river starts to swing in bends called meanders.
- Lower course (plain): slow and wide. In a flood, water spreads over the land and leaves mud. This flat, fertile land is a floodplain. Small raised banks next to the river are called levees.
- Mouth: the river slows down in the sea and drops its last mud, building a delta, like the Ganga-Brahmaputra delta.
On the coast, waves are the sculptors. Strong waves hit cliffs and carve caves, arches and standing rocks called stacks. Gentle waves carry sand and drop it to make beaches, sandbars and spits. A beach lies where the land meets the sea and is shaped again by every tide.
Karst landforms: when rain dissolves rock
Rain picks up a little carbon dioxide from the air and becomes a weak acid. Limestone is a rock that this weak acid can dissolve, very slowly, along its cracks. The landscape left behind is called karst.
- Sinkholes: round holes where the ground sinks into a dissolved space.
- Caves: big hollows below the ground. Water dripping inside leaves stalactites (hang from the roof) and stalagmites (grow up from the floor).
- Towers and pinnacles: hard parts of rock left standing.
- Disappearing rivers: streams that vanish into holes and come out far away.
Karst is found in Meghalaya in India, around Guilin in China, in Slovenia and on Jeju Island. Only soluble rock such as limestone makes karst. Granite does not.
Landforms and human life, and protecting landscapes
| Landform | How people use it | Risk |
|---|---|---|
| Mountains | Water source, hydropower, forests, herding, tourism | Landslides, hard to build roads |
| River plains | Farming, towns, roads, trade | Floods |
| Volcanoes | Fertile soil, geothermal energy, tourism | Eruptions |
| Coasts | Ports, fishing, salt, beaches | Storms, rising sea |
| Karst | Caves for tourism, building stone | Sinkholes, water loss |
Some landscapes are so special that they are protected. A geopark is an area where rocks and landforms tell the story of the Earth and local people share and protect them. A World Heritage natural site is a place of outstanding natural beauty or science value that the world agrees to protect. Jeju's volcanic island and lava tubes are one example. Good visitors stay on paths, take away their litter and do not break rocks or caves.
Try it at home
Fold: put a cloth on a table and push its two sides together. Watch ridges rise. River: fill a tray with damp sand, make a slope and slowly pour water from the top. Find the valley, the bend and the little delta at the bottom. Karst: drop a few drops of vinegar on a piece of chalk (a limestone cousin) and watch it fizz. Predict first, then check.
Key formulas and definitions
- Landform = a natural shape of the land
- Internal forces build; external forces wear down
- Erosion → transport → deposition
- Magma = melted rock underground; lava = melted rock on the surface
- Limestone + slightly acid rain → sinkholes and caves (karst)
Worked examples
1. A flat, fertile area next to a river is sometimes covered with fresh mud after a flood. Name it and say how it formed.
It is a floodplain. When the river overflows, the water spreads and slows down, so it drops the mud it was carrying. Each flood adds a new layer of rich soil.
2. Why are the highest mountains in the world, like the Himalaya, called young fold mountains?
They were made (in geological time) recently, when two plates pushed together and folded the rock upward. They are still being pushed up, and rain and ice have not had time to wear them down, so they are tall and sharp.
3. A village is on land full of round holes and caves. A river flows in and disappears. Which rock and landform is this?
The rock is limestone and the landform is karst. Rainwater dissolved the rock along cracks, making sinkholes and caves, and the river runs underground.
4. Why do most big cities and ports lie on plains and coasts and not high on mountains?
Plains are flat and have fertile soil, water and easy roads. Coasts allow ships and fishing. Mountains are steep and cold, so building, farming and roads are hard.
Common mistakes
- Thinking every mountain is a volcano. A volcano is built by lava coming out. Fold mountains are made by squeezing rock.
- Mixing up magma and lava. Magma is underground, lava is on the surface.
- Thinking landforms never change. They change all the time, slowly by rain and rivers, suddenly by eruptions and floods.
- Thinking karst forms in any rock. Only rocks that dissolve, like limestone, make karst.