Weathering breaks rock into smaller pieces. Water seeps into cracks, freezes and expands, and splits the rock; this is called freeze-thaw. Plant roots grow into cracks and push them apart. Rain that is slightly acidic slowly dissolves rocks like limestone.
Erosion carries the broken pieces away. Rivers carry sand and pebbles downstream, rubbing them smooth and round. Waves wear away cliffs and form beaches and caves. Wind blows sand and scrapes rock in deserts. Glaciers scrape out wide U-shaped valleys. Faster water carries bigger stones, and the steeper the slope, the faster the erosion.
Worked example
Why are pebbles on a beach round and smooth?
- Waves roll the pebbles against each other.
- Their sharp edges are knocked and rubbed off.
Answer:After a long time they become round and smooth.
Key words
- freeze-thaw
- water freezing in cracks and splitting rock
- deposition
- dropping sand and stones in a new place
- glacier
- a huge slow river of ice
- sediment
- bits of rock carried by water or wind
Practise this
New questions every time.
NGSS-referenced: 4-ESS2-1