- Distinguish the internal and external forces that shape relief
- Work out absolute and relative height
- Classify plains and mountains by height
Imagine standing on the summit of Bazarduzu (4466 m) in the morning and walking along the Caspian shore, below sea level, in the evening. Within one country the difference in height is almost 4.5 km! Geographers call this variety of the Earth's surface relief.
Relief and the forces that shape it
All the ups and downs of the Earth's surface taken together — mountains, plains, valleys and depressions.
Relief is formed by two groups of forces working together. Internal forces — plate movements, volcanism and earthquakes — raise mountains and create depressions. External forces — weathering, running water, wind, glaciers and sea waves — wear the heights down, carry the debris away and drop it in low places. So internal forces build relief up, while external forces smooth it out.
- Rivers cut valleys and canyons and build deltas at their mouths.
- Wind piles up sand hills called dunes in deserts.
- Glaciers scoop out deep hollows in mountains and move huge amounts of rock.
- Temperature changes and water crack and break rocks into pieces — this is weathering.
Absolute and relative height
Absolute height (elevation) shows how far a point is above (or below) sea level. Relative height is how much higher one point is than another. All heights shown on maps are absolute heights.
Leyla's mountain village is 1200 m above sea level. A nearby peak has an absolute height of 3700 m. How high is the peak relative to the village?
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3700 m − 1200 m = 2500 m.
So Leyla has to climb 2.5 km to reach the top.
Plains and mountains
| Landform | Absolute height | Example |
|---|---|---|
| Depression | below sea level | Dead Sea shore (more than 400 m below) |
| Lowland | 0–200 m | Amazon Lowland, Kura-Araz Lowland |
| Upland | 200–500 m | Central Russian Upland |
| Plateau | above 500 m | Central Siberian Plateau |
| Low mountains | up to 1000 m | usually old, heavily worn-down mountains |
| Medium mountains | 1000–2000 m | Ural Mountains |
| High mountains | above 2000 m | Caucasus, Himalayas |
The highest point of a mountain is its summit (peak), its sloping sides are slopes, and the place where it meets the plain is its foot. The world's highest peak is Mount Everest (Chomolungma) in the Himalayas — about 8849 m. The largest lowland on the continents is the Amazon Lowland in South America.
The relief of the ocean floor
- Continental shelf — the shallow underwater edge of a continent, usually up to about 200 m deep.
- Continental slope — the steep drop from the shelf to the ocean bed.
- Ocean bed — vast plains 3–6 km deep, crossed by mid-ocean ridges.
- Deep-sea trenches — the deepest places. The Mariana Trench in the Pacific is about 11,000 m deep.
Key points
- Relief is shaped by internal forces (plate movement, volcanism) and external forces (water, wind, ice, weathering).
- Absolute height is measured from sea level; relative height from another point.
- Plains: lowlands (0–200 m), uplands (200–500 m), plateaus (above 500 m).
- High mountains rise above 2000 m; the highest peak is Everest (about 8849 m).
- The ocean floor has a shelf, a continental slope, the ocean bed and deep trenches.
Check yourself
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