1. Forces wear down and build up earth’s surface
5.1 notes

2. Think about…
How did natural forces shape this landform?

3. Natural forces move and deposit sediments
Valleys and canyons are formed by the movement of water.

4. Natural forces move and deposit sediments
The process in which weathered particles are picked up and moved from one place to another is called erosion.

5. Natural forces move and deposit sediments
The part of the erosion process in which sediment is placed in a new location (deposited) is called deposition.

6. Natural forces move and deposit sediments
The force of gravity is an important part of erosion and deposition.

7. Natural forces move and deposit sediments
Gravity causes water to move downward, carrying and depositing sediment as it flows.

8. Natural forces move and deposit sediments
Gravity can pull huge masses of ice slowly down mountain valleys.

9. Natural forces move and deposit sediments
Gravity causes dust carried by the wind to fall to Earth.

10. Natural forces move and deposit sediments
Erosion of weathered rock by movement occurs in 3 major ways:

11. Natural forces move and deposit sediments
1. Water
Rainwater and melting snow carry rock and soil particles down sloping land, eventually depositing them on river bottoms and riverbanks.

12. Natural forces move and deposit sediments
Waves in oceans and lakes also carry sediment and deposit it to form beaches and other features.

13. Natural forces move and deposit sediments
2. Wind
Strong winds lift tiny particles of dust and carry them long distances.
When the wind dies down, the particles drop to the ground.

14. Natural forces move and deposit sediments
3. Ice
As ice moves slowly downhill, it transports rock and soil particles that are embedded in it.

15. Gravity can move large amounts of rock and soil
Many homes can be found along the beautiful cliffs of coastal California.
Why might this be a risky place to build a house?

16. Gravity can move large amounts of rock and soil.
Many coastal and mountainous regions have landslides.
A landslide is a type of mass wasting-the downhill movements of masses of rock and soil.

17. Gravity can move large amounts of rock and soil.
In mass wasting, gravity pulls material downward.
There is often a trigger event, such as heavy rain or an earthquake.

18. Gravity can move large amounts of rock and soil.
Mass wasting can occur suddenly or gradually.
It can involve tons of rock sliding quickly or gradually moving a little at a time.

19. Gravity can move large amounts of rock and soil.
Mass wasting can be classified by the type of material that is moved and the speed at which it is moved.

20. Gravity can move large amounts of rock and soil.
A sudden, fast, movement of rock and soil is called a landslide.

21. Gravity can move large amounts of rock and soil.
Movement of mud or soil is described as a mudflow.

22. Mass wasting of rock
Mass wasting of rock includes rockfalls and rockslides.

23. Mass wasting of rock
A rockfall is when individual blocks of rock drop suddenly and fall freely down a cliff or steep mountainside.

24. Mass wasting of rock
A rockslide is when a large mass of rock slides as a unit down a slope.
Rockslides can reach speeds of 100 km/hr!

25. Mudflow
A mudflow is the mass wasting of debris with large amounts of water.
Debris is a mixture of rock, soil, and plants.

26. Mudflow
Mudflows often happen in canyons and valleys after heavy rains.
The soil becomes so heavy that the slope can no longer hold it in place.

27. Mudflow
Mudflows also occur on active volcanoes.

28. Mudflow
In 1985, a huge mudflow caused by a volcano destroyed the town of Armero, Colombia, and killed more than 20,000 people.

29. Mudflow
The eruption of Mt. St. Helens in caused mudflows that traveled more than 90 km from the mountain!

30. Slumps and creep
A slump is a slide of loose debris that moves as a single unit.
Slumps can occur along roads and highways where construction has made slopes unstable.

31. Slumps and creep Creeps are the slowest form of mass movement.
The soil or debris moves at a rate of mm per year-too slow to be directly observed.

32. Slumps and creep
Creep can affect buildings as well- sometimes enough to crack walls!
The wetter the soil, the faster it will creep.

33. Review
1. The main natural force responsible for mass movements of rocks and debris is
A. rainwater
B. wind
C. gravity
D. fire