Unit 8 Lesson 1 How Do Weathering and Erosion Shape Earth’s Surface? Copyright © Houghton Mifflin...

Unit 8 Lesson 1 How Do Weathering and Erosion Shape Earth’s Surface?

Copyright © Houghton Mifflin Harcourt Publishing Company



Objectives: Compare weathering and erosion. Explain the causes of weathering and erosion. Describe how erosion and deposition change Earth’s

surface.

Vocabulary:• Weathering• Erosion• Deposition• Sediment



What Can Break a Boulder?

• The process of rock breaking apart is called weathering.



What Can Break a Boulder?• Causes:

• gravity, • flowing

water• blowing

sand• living things• wind• rain• chemicals


Rocks on the Move

• Weathering is the beginning of a series of changes that often occurs to rocks on Earth’s surface.

• The process of moving weathered rock from one place to another is called erosion.

• Moving water is one of the most common causes of erosion.



Rocks on the Move• Fast-moving water and gravity can cause rocks to move

downhill.

• As the water in a river slows down, it has less energy and cannot move the largest rocks and pebbles.

• The dropping of weathered rock by wind or moving water is known as deposition.



Rocks on the Move• Slow-moving water has less energy than fast-moving

water has. Thus, as water in a river continues to slow down, more bits of weathered rock are dropped.

• Slow-moving water carries only very small pieces of rock, such as sand and silt, called sediment.



Rocks on the Move• What size of sediment drops out first? What size

drops out last?



Rocks on the Move

• When rivers reach the ocean, they slow down even more and sediment is dropped. Over time, the sediment forms a landform called a delta.



Exit slips Active reading



Homework brain check



Exit slip braincheck



Blowing in the Wind• A landform is a natural land

shape or feature. Weathering and erosion by wind change landforms.

• Wind can carry sediment from place to place. When wind deposits a lot of sand in one area, sand dunes form.



Blowing in the Wind• Wind sweeps up one side of a dune and lifts sand

from its surface. Gravity pulls the sand down the other slope.



Blowing in the Wind• Blowing sediment can also

cause changes to other landforms as particles collide with exposed rock to form interesting shapes.

• For instance, mushroom rocks and arches are formed by water but shaped by the wind. Eventually, gravity pulls these formations down.



Ice Carvings• Huge sheets of ice are called

glaciers and are found in very cold places.

• Gravity pulls glaciers downhill, picking up soil, rocks, and boulders beneath the glacier and pushing boulders against the ground below.

• When the glacier melts, the rock and sediment it carried downhill drop out and form different land features, including hills called moraines.



Ice Carvings• A huge glacier once

covered most of Canada and the northern United States. The ice cut deep grooves that formed the Great Lakes.



Exit slip Active reading



Can Waves Cut Caves?• Moving water causes weathering

and erosion by picking up sediment, which scrapes against the bottom and sides of the riverbed.

• This carves out deep canyons, which are gorges between cliffs of rock.

• Deposits of sediment can change the direction of river water. Curves in a river’s path can produce different landforms.



Can Waves Cut Caves?• Ocean waves weather

cliffs, eroding pieces of rock and depositing them into new places, forming caves in shoreline cliffs.

• The sediment from eroding shorelines becomes fine sand, and beaches are formed at the water’s edge.



Homework Braincheck



Do Plants Protect Soil?• In the early 1900s, families in

the central plains of the United States made a living farming land where natural grasses once grew.

• In between crop seasons, loose soil was left exposed to wind.

• During the 1930s, the plains experienced severe drought. The soil turned to fine, dry dust, and high winds caused giant dust storms.



Do Plants Protect Soil?• These dust storms stripped

away much of the soil that made the region good for farming.

• Families moved away to find other ways to survive. They suffered hard times. The region became known as the Dust Bowl.

• The Dust Bowl teaches a valuable lesson about erosion problems caused by removing all the plants from an area.



Do Plants Protect Soil?• Now farmers plant

different crops at different times to keep soil covered year-round.

• Fences and lines of trees are planted to break the wind, and plants are added to hillsides to protect soil from water erosion and wind.


Unit 8 Lesson 1 How Do Weathering and Erosion Shape Earth’s Surface? Copyright © Houghton Mifflin...

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