How wind and water move rock from one place to another
Macmillan California Science • Grade 4 • Pages 202–209
The movement (transport) of weathered rock from one place to another by wind, water, or ice.
The dropping off of weathered rock, sand, and soil in a new place after being carried by wind or water.
Small pieces of rock, sand, and soil that are carried by wind or water during erosion.
The wearing away of rock by the sharp edges of sand or other sediment carried by wind.
A method of farming where crops are planted in alternating strips — one strip holds soil, the next grows food, and they switch each year.
A method of plowing fields across a slope (not up and down) so the shape of the land prevents soil from washing away.
To use methods that save and protect a resource, like soil, from being wasted or lost.
A period in the 1930s when drought and overfarming caused massive dust storms across the American Southwest, destroying farmland.
Textbook pages 204–205
You already learned that weathering breaks rocks into smaller pieces. But what happens to those pieces next?
The transport of weathered rock from one place to another is called erosion. Weathering and erosion work together to change and shape the land. Weathering breaks the rock down, and erosion moves the pieces.
KEY IDEA
Weathering breaks rock. Erosion moves it. They work together to reshape the land.
Flowing water is the biggest cause of erosion. Here's how it works:
Waves also cause erosion. First, waves break rocks apart. Then the waves carry the rocks and sand to a new place.
Wind picks up very small pieces of rock, sand, and soil and carries them to other places. This is erosion by wind. At the same time, wind weathers rock by abrasion — the sharp edges of blowing sand scrape and wear down the rock surface.
🌊 Real World Example
The Mississippi River is the 2nd longest river in the US. Its nickname is the "Muddy Mississippi" because it carries so much sediment that parts of the water look brown!
After wind or water picks up and carries bits of rock, sand, and soil, it eventually drops them off. The dropping off of weathered rock is called deposition.
REMEMBER THE DIFFERENCE
Erosion = picking up and moving sediment | Deposition = dropping sediment off in a new place
Quick Check — From Your Textbook (p. 205)
Cause and Effect: What are two causes of erosion?
Answer: Flowing water (the biggest cause) and wind.
Critical Thinking: How do weathering and erosion work together?
Answer: Weathering breaks rocks into smaller pieces (sediment). Then erosion moves those sediments to new places by wind or water.
Textbook pages 206–207
Some soils and rocks erode faster than others. Several things affect how quickly erosion happens:
| Factor | Erodes Faster | Erodes Slower |
|---|---|---|
| Soil Type | Sandy soil (loose, easily blown or washed) | Hard-packed clay (sticks together) |
| Sediment Size | Small pieces like sand (light, easy to move) | Large pieces like pebbles (heavy, hard to move) |
| Wind & Water Strength | Strong winds, floods, heavy rain | Gentle breezes, light rain |
| Plants | No plants (bare soil, nothing to hold it) | Plants present (roots hold the soil in place) |
TEST TIP
If the teacher asks "Which erodes faster — sandy soil or clay?" the answer is sandy soil. If they ask about sediment size, remember: smaller = easier to erode.
The Dust Bowl is one of the most dramatic examples of erosion in American history. Here's what happened:
Farmers in the Southwest farmed huge areas of land. Harvests were plentiful at first.
The soil became overused and worn out. Crops grew poorly.
Almost no rain for nearly 10 years. Crops wouldn't grow. The soil was bare and dry.
Without plants to hold the soil, strong winds blew the dry soil away. Terrible "black blizzards" — thick clouds of dust — swept across the land for miles. Dust got into houses, closets, and on dishes.
Up to 30 cm (12 inches) of topsoil were lost in some places. Animals died because there were no plants to eat. Thousands of farmers had to leave their homes and move west.
🗺️ Where Was the Dust Bowl?
The Dust Bowl mainly affected the Southwest region of the United States. The textbook map shows the Dust Bowl area covering parts of Kansas, Oklahoma, Texas, New Mexico, and Colorado.
Quick Check — From Your Textbook (p. 207)
Cause and Effect: What caused the Dust Bowl?
Answer: Overfarming wore out the soil, then a drought starting in 1930 meant no rain for years. Crops died, the soil became bare and dry, and strong winds blew it away.
Critical Thinking: Which might erode the sides of a stream faster — a flood or a drought?
Answer: A flood. Floods have strong, fast-moving water that carries away lots of sediment. During a drought there is less water, so less erosion.
Textbook page 208
The Dust Bowl taught people that it was important to conserve soil. Today, farmers use several methods to slow erosion:
Farmers plant rows of trees between fields to block the wind and slow wind erosion. These act like a "living fence."
Crops planted in alternating strips. One strip has plants to hold soil; the next has food crops. Strips are switched each year.
On sloped land, farmers plow across the slope (not up and down). The curved rows hold water and prevent soil from washing downhill.
WHY PLANTS MATTER
Plant roots act like anchors in the soil. They hold the soil together and keep it from blowing or washing away. That's why the Dust Bowl happened — without plants, there was nothing to hold the dry soil in place.
Quick Check — From Your Textbook (p. 208)
Cause and Effect: If farmers use contour plowing, what will happen?
Answer: The shape of the plowed land will prevent soil from eroding. Water will follow the curved rows instead of running straight downhill, so less soil is washed away.
Critical Thinking: Could the Dust Bowl happen again? Explain.
Answer: It could if farmers stopped using soil conservation methods and another long drought hit. But it's less likely today because farmers use strip farming, contour plowing, and plant trees to protect the soil.
Erosion and deposition move sediments
Erosion picks up weathered rock and moves it; deposition drops it in a new place. Together they reshape Earth's surface.
Erosion rate depends on several factors
Soil type (sandy = faster), sediment size (smaller = faster), strength of wind/water, and whether plants are present.
Farmers conserve soil
Planting trees, strip farming, and contour plowing all slow erosion and protect farmland.
Practice answering these — they're directly from the textbook's Lesson Review section.
1. Main Idea: What do wind and water do to land?
They erode (move) weathered rock from one place to another, then deposit it in new places. This reshapes the land over time.
2. Vocabulary: What is deposition?
Deposition is the dropping off of weathered rock, sand, and soil that was transported by wind or water.
3. Cause and Effect: What are some causes of erosion? What are some effects?
Causes: flowing water, waves, wind. Effects: land is reshaped, sediments are carried to new places, riverbeds change, soil is lost from farms.
4. Critical Thinking: How is erosion different from deposition?
Erosion is the picking up and moving of sediment. Deposition is the dropping off of that sediment in a new place. They're opposite parts of the same process.
5. Test Practice: Which one of the following causes erosion?
C. Waves (not soil, sunlight, or cracks in rocks)