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Cause and Effect — what shapes the Earth’s surface?
Internal forces
Act from within the Earth — earthquakes, volcanoes, folding and faulting
build up
mountains, valleys and ocean basins
↓
External forces
Weathering, erosion and deposition slowly
wear the land down
and reshape it
↓
Effect: the diverse landforms we see today — from the highest peaks to the deepest ocean floors, on which human life depends
🔸 Key Points — Before We Move On
- The Earth is made of three layers — crust, mantle and core.
- Internal forces (earthquakes, volcanoes, folding, faulting) move the crust and build up mountains, valleys and ocean basins.
- External forces — weathering, erosion and deposition — carve smaller landforms and affect human life.
- The surface is shaped by agents of gradation : running water, waves, glaciers, wind and underground water.
- Disasters — landslides, avalanches, GLOFs and dust storms — are linked to particular landforms.
Key Terms
- Landform
- A natural feature on the Earth’s surface, such as a mountain, valley, plateau, plain, delta or coast.
- Lithosphere
- The rigid outer layer of the Earth, made of the crust and the upper part of the mantle; it is broken into tectonic plates.
- Asthenosphere
- The soft, semi-molten layer just below the lithosphere (the lower part of the mantle) over which the plates slowly move.
- Tectonic plate
- A large slab of the lithosphere that moves slowly over the asthenosphere; plates may be continental, oceanic or mixed.
- Convection currents
- Slow circulating movements in the hot mantle, driven by the Earth’s internal heat, that drag the plates along.
- Plate boundary
- The line where two plates meet; it may be convergent (colliding), divergent (moving apart) or transform (sliding past).
- Ring of Fire
- A horseshoe-shaped belt around the Pacific Ocean with most of the world’s earthquakes and volcanoes.
- Weathering
- The breaking down of rock into smaller pieces on the spot, with no movement of the pieces; it may be physical, chemical or biological.
- Erosion
- The wearing away and carrying away of soil and rock by natural agents like water, wind, ice and waves.
- Deposition
- The dropping of eroded material in a new place, where it builds landforms such as deltas, beaches and plains.
- Agents of gradation
- Natural forces — running water, waves, glaciers, wind and underground water — that wear down high land and fill low land.
- Meander
- A winding curve or bend in the middle or lower course of a river, formed by erosion on the outer bank and deposition on the inner bank.
- Delta
- A fan-shaped or triangular area of fertile land built where a river deposits its sediment at its mouth.
- Moraine
- Rock, soil and debris (till) carried and left behind by a glacier when it melts.
- Karst topography
- The landscape of caves, stalactites, stalagmites and sinkholes formed where underground water dissolves limestone.
- Landslide
- The sudden sliding of soil and rock down an unstable, often rain-soaked slope.
- Avalanche
- A sudden slide of unstable snow down a steep mountain slope.
- GLOF (Glacial Lake Outburst Flood)
- A destructive flood caused when a glacial lake’s natural ice or moraine dam suddenly collapses.
- Dust storm
- Strong winds lifting large amounts of loose, dry soil and sand into the air, common in deserts and dry regions.
