What causes changes to Landforms?

Vocabulary:Weathering

ErosionDelta

Sinkhole

Weathering

• In weathering, rock or other materials are worn away.

• Wind, water, and plant roots are some causes of weathering.

• Weathered rock can have an usual shape.

Erosion• The movement of

sediment, such as soil, sand, or weathered pieces of rock.

• The sediment is carried away from a landform.

• Wind, water, and ice can all cause erosion.

Delta

• A new land that forms where a river empties into the ocean.

• The river deposits sediment there.

• Over time, the sediment builds up new land.

Sinkhole

• A large hole that is the result of underground erosion. Water carves out a cave near the surface. When the cave collapses, a sinkhole appears.

Changes Caused by WindWhen wind blows sand

against a rock, the rock changes. The blowing sand breaks the rock into smaller pieces. That process is called weathering.

Wind then carries weathered pieces of rock away. They settle when the wind slow down. Over a long period of time, the pieces may pike up and form sand dunes.

Sand dunes are found in deserts and near oceans and lakes. Dunes on the Atlantic coast protect the land during storms. But dunes that move inland can damage roads and buildings.

Quick Check

1. How does wind cause weathering?

2. Where can you find sand dunes?

Changes Caused by Moving Water Moving water can change

landforms. It carries away soil and small pieces of rock, also called sediment. Erosion is the process of moving sediment by wind, water, and ice.

Moving water makes many changes to land. It can form a canyon. It can erode the sides or bottom of a river. The water carries the sediment downstream. When the water slows down, the sediment settles to the bottom of the river.

Quick Check

1. What causes erosion?

2. Name one way that water can change a river.

Erosion and DepositionFast wind has more

energy than slow wind.The same is true of moving water. The more energy wind or water has, the more sediment it can carry. So the faster wind or water moves, the more erosion it causes.

Rain can cause erosion. As it runs down a hill, it carries sediment away. Over time, rain may leave gullies, or ditches, in the ground.

Ocean waves cause erosion. They carry away pieces of rock from the shore. That process may form cliffs.

Erosion and Deposition

Ocean waves cause another kind of change. They bring sand to the shore. That is an example of deposition. Deposition is the process by which sediment drops out of the water.

Deposition happens when water slows down. The water in a river slows down at its mouth. That is where the river meets the ocean. Deposition at a river’s mouth can form new land. That land is called a delta.

Quick check

1. What causes a gully?

2. Draw a picture of what the cliff may look like if ocean waves erode it for another 100 years?

3. How does a delta form?

Sinkholes and LandslidesErosion can happen

underground. Sometimes water weathers and erodes soft rock under the surface. That forms a cave. Often, the roof of the cave falls in. If the cave is near the surface, a big hole may open suddenly. That is called a sinkhole.

Gravity can also change landforms. It can make soil, mud, and rocks move quickly down a slope. This form of erosion is called a landslide. Some landslides occur after heavy rain. Others are started by earthquakes.

Plants

Plants can cause weathering and erosion when their roots grow into cracks in rock. As the rocks get bigger, they break up the rock.

But plants also prevent erosion. That is because plant’s roots hold soil and sand in place. Farmers use that fact to protect land they are not using. They plant cover crops to slow down erosion.

The same protection works naturally. Plants grow on sand dunes help stop erosion. The plants’ roots hold the sand in place.

Lesson Review

1. Blowing sand dunes causes ____________ when it breaks rocks into smaller pieces.

2. When deposition forms new land at a river’s mouth, the land is called a ____________.

3. When an underground cave near the surface collapses, the effect is a ______________.

4. Cover crops help stop _____________ because plants roots hold soil in place.