50-minute lesson
Grade 4 Science: Weathering and erosion
Lesson objective
- Explain the difference between weathering and erosion.
- Model how running water erodes soil.
- Describe ways to reduce soil erosion.
Success criteria:
- I can explain weathering and erosion in my own words.
- I can use a sand tray to show water carrying soil away.
- I can explain why plant roots help stop erosion.
Materials
- A shallow baking tray or plastic tub
- Sand or garden soil
- A small block or book to tilt the tray
- A watering can or plastic cup with small holes poked in the bottom (adult to poke holes)
- A handful of grass clippings, leaves or a strip of turf
- A bucket or tray to catch runoff, or do it outdoors
Introduction
5 minIntroduce today's words:
- weathering: The breaking down of rock into smaller pieces by wind, water, ice, temperature changes or living things.
- erosion: The carrying away of broken rock and soil by water, wind or ice.
- sediment: Small pieces of rock and soil that are carried and dropped by water or wind.
- deposition: When moving water or wind drops the sediment it is carrying.
- landform: A natural feature of Earth's surface, such as a hill, valley or cliff.
Ask your child what they already know about weathering and erosion.
Explanation
10 minEarth's surface is always changing, mostly very slowly. Two important processes are weathering and erosion.
Weathering breaks rock into smaller pieces. Rain, wind, frost, plant roots growing into cracks and heating and cooling of rocks in the sun can all cause weathering.
Erosion carries those pieces away. Rivers carry soil downstream, waves wear away cliffs and wind blows sand across deserts.
Eventually the moving water or wind slows down and drops its load. This is called deposition. Sand bars and river deltas form this way.
These processes shaped many Australian landforms. Waves eroded soft limestone cliffs on the Victorian coast to leave rock stacks like the Twelve Apostles. Uluru has been shaped by weathering and erosion over many millions of years.
Plants help protect soil. Their roots hold soil together and their leaves soften the impact of raindrops. Bare soil erodes much faster.
Worked examples
8 minSand-tray river
What happens when 'rain' falls on a sloping tray of sand?
Step 1: Fill the tray with damp sand and pat it flat.
Step 2: Prop up one end with a block so it slopes.
Step 3: Slowly sprinkle water at the top using the cup with holes.
Step 4: Watch: small channels form and sand is carried down and dropped at the bottom.
Answer: The water erodes channels and deposits sand at the lower end.
Does covering the soil help?
Compare bare sand with sand covered in grass clippings.
Step 1: Set up two trays the same way, with the same slope.
Step 2: Cover one tray with grass clippings or leaves.
Step 3: Pour the same amount of water on each in the same way.
Step 4: Compare how much sand washes to the bottom.
Answer: Less sand washes away from the covered tray, so plant cover reduces erosion.
Guided practice (do together)
10 min1. What is weathering?
(a) Rock being carried away by a river (b) Rock being broken into smaller pieces (c) Rain falling from clouds (d) Sand being dropped in a delta
2. Which is an example of erosion?
(a) A river carrying soil downstream (b) Ice forming in a freezer (c) A seed sprouting (d) Clouds forming
3. How do plant roots help stop erosion?
(a) They make rain stop (b) They hold the soil together (c) They turn soil into rock (d) They make the wind stronger
4. Which mainly shaped the Twelve Apostles on the Victorian coast?
(a) Volcanoes (b) Earthquakes (c) People digging (d) Waves eroding the cliffs
Independent practice
12 min5. In the sand-tray test, which change would make it a fair test?
(a) Using a steeper slope for one tray (b) Pouring more water on one tray (c) Keeping the slope and amount of water the same (d) Using different sand in each tray
6. When moving water slows down and drops the sand it carries, this is called d__________.
7. Small pieces of rock and soil carried by water are called s________.
8. Which erodes faster: bare soil or soil covered with plants?
Questions to check understanding
- Can you explain weathering and erosion in my own words?
- Can you use a sand tray to show water carrying soil away?
- Can you explain why plant roots help stop erosion?
- What was the trickiest part today?
Answer guide
1. Rock being broken into smaller pieces — Weathering breaks rock down; erosion carries it away.
2. A river carrying soil downstream — Moving water carrying soil away is erosion.
3. They hold the soil together — Roots bind soil so water and wind cannot easily carry it away.
4. Waves eroding the cliffs — Waves wore away soft limestone, leaving stacks of rock standing in the sea.
5. Keeping the slope and amount of water the same — Only the ground cover should change; everything else stays the same.
6. deposition — Dropping sediment is deposition.
7. sediment — These small pieces are sediment.
8. bare soil — Bare soil has nothing to protect it from rain and wind.
Review
5 minRecap the success criteria together. Watch for these common misconceptions:
- Students often mix up weathering and erosion. Weathering breaks; erosion moves.
- Some think landforms never change. Most change too slowly to see in a lifetime, but floods and storms can change them quickly.
- Some believe only water causes erosion. Wind and ice also erode.
Extension activities
- After rain, look for signs of erosion around your garden, footpaths or a local creek.
- Use a fan on low to model wind erosion on dry sand (wear sunglasses to protect eyes).
- Find photos of Australian landforms and decide whether wind, water or ice shaped them.
Suggested follow-up
- Revisit weathering and erosion tomorrow with two or three quick questions from memory.
- Try the online practice check for this topic and look at any questions that need another go.
Tips for parents
- Do this activity outside or in a bathtub to manage mess.
- Measure the 'rain' with a cup so each tray gets exactly the same amount.
- Safety: an adult pokes holes in the cup; wash hands after handling soil and wear gloves if you have cuts.