Discovery Education Science P4: Term 2, Unit 4, pp. 135–148
GoalInvestigate a slope with running water, map where the land changed, and match landforms to how they could have formed.
New words
slope · ground that is tilted, so one end is higher than the othermap · a drawing from above that shows where things areinvestigate · to look closely and test to find out
Explanation
Scientists who study the land are like detectives. They search a place for clues and ask what changed it. You can do the same in a school yard, a garden or a park. First, draw the main areas and label them. Then find a gentle slope, pour water down it from a bottle and watch. Mark each place where the ground changes: a tiny channel where soil is washed away, which is erosion, a little pile of soil at the bottom, which is deposition, and a cracked, crumbling paving stone, which shows weathering. Put your marks on the map. Steeper slopes make water run faster, so they usually show more erosion. Small changes in a yard look like the big changes in canyons and mountains, only smaller. Knowing the signs of erosion helps people choose where to build a house or plant a crop.
Clue on the map
Process
What it shows
tiny channel
erosion
soil washed away
little pile at the bottom
deposition
soil dropped here
round, smooth stone
weathering
edges worn off
Worked examples
Slope
Height
Channel length
gentle
3 cm
12 cm
steeper
6 cm
20 cm
Slope test. Seif props a tray of damp soil on 1 book that is 3 cm thick and pours a cup of water at the top. A channel 12 cm long forms. He props it on 2 books (6 cm) and repeats it. This time the channel is 20 cm long. The steeper slope gave more erosion.
Picture
Quick or slow?
Why?
soil on the road
quick
a lot moved at once
river around a hill
slow
rock wears away a little at a time
Visual walkabout. A photograph shows a hillside with soil spread over a road after heavy rain. Mina says the change was quick, because a lot of soil moved at once. Another photo shows a river that has worn away rock around a hill: she says that change was slow.
bare slope→rain erodes soil→danger to the house→plant trees
Predicting. A house stands at the top of a bare slope that is losing soil each rainy season. Habiba predicts that the slope will keep eroding and the house may be in danger. People could plant trees to hold the soil, or build somewhere else.
Class activity
Slope detectives. With a grown-up, find a gentle slope in your garden or yard, or prop a tray of damp soil on a book. Draw a map of the area. Pour a cup of water slowly at the top. Mark on your map where the soil changed: a channel, a pile, a wet patch. Then raise the tray on one more book and pour again. Which slope made the longer channel? Wash your hands afterwards.
Practice
1
Water runs down a slope and carries soil away, leaving a small channel. Which process is this?
Erosion.
2
A tray on 2 books (3 cm each) has how high a slope?
2 × 3 = 6 cm.
3
Why do steeper slopes usually show more erosion?
Water runs faster down a steeper slope, so it carries more soil.
4
Why is it useful to recognise signs of erosion before building a house?
You can avoid building on land that is wearing away.
