Geography · Rung 7 of 12

Rivers and lakes

A river is not a line, it is a basin: all the ground that drains into it, separated from its neighbour by a watershed. The Amazon basin is the world's largest, seven million km², and its river carries more water than the next six combined; the Nile is longer but carries little, because it crosses a desert and loses water on the way. At the mouth, if the sea is calm and the river brings plenty of sediment, a delta forms; if the tide is strong, an estuary carries it away. Lakes rank too: the Caspian is the largest but salty and has no outlet, Superior the largest freshwater lake by area, and Baikal the deepest at 1,642 m, holding a fifth of the planet's liquid fresh water.

Where this sits

Comes after
The map and its signs

Exercises from this rung

Generated by the app, from easiest to hardest

  1. Which river carries more water to the sea than any other?

    • The Amazon
    • The Nile
    • The Yangtze
    • The Congo

    Why The Amazon discharges about 209,000 m³ per second, close to 20 % of all the fresh water reaching the ocean worldwide. Its basin is the planet's largest, seven million km², collecting the rain of the biggest rainforest there is. It pushes so much fresh water out that it is measurable more than a hundred kilometres offshore. The Congo is second, with a fifth of it.

    easier

  2. The Amazon basin takes up much of this continent. How much fresh water does it carry to the sea?

    • A fifth
    • A hundredth
    • Nearly all of it
    • Half

    Why The Amazon discharges some 209,000 m³ per second, around 20 % of all the fresh water rivers carry to the oceans, more than the next seven combined. Its flow is so great that the water is still fresh over a hundred kilometres out to sea, which is why early navigators called it “the freshwater sea”.

    in between

  3. What is a watershed?

    • The line of ground separating two basins
    • The point where a river splits in two
    • A lake shore
    • The boundary between fresh and salt water

    Why It usually follows the summits, and on a topographic map it draws itself: it is the line joining the highest points between two valleys. Two drops landing a metre apart can end in different oceans. The Americas' continental divide crosses the Rockies and the Andes and separates what goes to the Pacific from what goes to the Atlantic; in Europe, the Alps separate the Mediterranean from the North Sea.

    harder