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Lessons 8-9

Use your dictionary to find a definition of erosion.

Read the following then answer the questions

Water always finds the easiest route off mountains and hills. Mountain streams are often
small but flow very fast because of the steep slopes. Pieces of stone and rock are carried

by the streams. As they are bounced along the bottom of the stream they wear away at it
and eventually cut out more stones, making the river bed deeper.

In the same way rocks are thrown against the river banks where the river turns a corner.
These wear away at the bank and carry more rocks downstream. This wearing away is called
erosion. Eventually the V-shaped valley begins to form.

Rain flows into cracks in the rock. In cold weather it freezes and expands. When this occurs
the rock often shatters and falls away. This is known as frost shattering. A large amount of

this rock is known as scree.

In very hot regions, the temperature is constantly heating and cooling each day, sometimes
with great variations in temperature between day and night.
Rocks expand when they are heated up so eventually they crack and fall away.

This is known as heat shattering and is common in deserts.

Some rocks, especially limestone, dissolve in water. Cracks in the rock widen as the water
washes through from rain or rivers above. Eventually some rivers flow underground and

dissolve more rocks to form huge caves. Examples are found in the Peak District in England.

(God's Amazing Landscapes) 45