Soil
Primary 4 · Science and Elementary Technology
Soil
Lesson 4 of 5
15 min
Let's begin
After a heavy storm, Habimana looks down at the Nyabarongo river. It is brown, like milky tea. "Why is the river brown today?" he asks his teacher. "Because it is carrying our soil away," she says.
Soil erosion is the washing or blowing away of the top layer of soil by water or wind. This top layer, the topsoil, is the most fertile part. When it is lost, crops grow badly.
Rwanda is the "land of a thousand hills", and it has heavy rains. Rain running down steep, bare slopes can carry away a lot of soil.
| Type | What happens |
|---|---|
| Splash erosion | Big raindrops hit bare soil and splash tiny bits of it into the air. This is where erosion begins. |
| Sheet erosion | A thin, even layer of soil is washed off a whole field, like a sheet being pulled off a bed. It is hard to notice. |
| Rill erosion | Running water cuts many small, narrow channels (rills) in the soil. |
| Gully erosion | The rills grow into big, deep channels (gullies) that can swallow paths, fields and even houses. |
| Wind erosion | Wind blows loose, dry soil away as dust. |
On very wet, steep hills, a whole piece of hillside can slide down at once. This is a landslide, and it is very dangerous.
Tip
Splash, sheet, rill, gully: erosion grows bigger
It starts with a splash and can end in a gully, so stop it early!
Try each one first, then tap Show answer to check.
What is soil erosion?
Answer: The washing or blowing away of the top layer of soil by water or wind.
Why does the Nyabarongo turn brown after heavy rain?
Answer: Rainwater has washed soil from the hills into the river.
A farmer notices many small, narrow channels running down his field after rain. What type of erosion is this?
Answer: Rill erosion. If he does nothing, the rills can grow into gullies.
Give three human activities that cause soil erosion.
Answer: Any three of: cutting down trees, overgrazing, bush burning, digging up and down slopes, mining and quarrying.
What you learned today
Sources and credits
The exercises (Try it yourself and the practice questions) are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Erosion grows bigger. Put these in order, from smallest to biggest.
Tap the cards in the right order.
