1. Wearing Down Earth’s Surface
Unit C
Chapter 6 Lesson 2
C14 – C19

2. Objectives
Identify destructive forces as processes that wear down Earth’s land features.
Identify weathering as a destructive force.
Recognize that weathering can be either mechanical or chemical
Define erosion as the carrying away of weathered rock by water, wind, and glaciers.

3. Main Idea
Destructive forces, such as weathering and erosion, wear down Earth’s surface features.

4. Vocabulary
Erosion – (noun), destructive force in which pieces of rock are moved by water, wind, or moving ice.
Sediment – (noun), small pieces of rock
Weathering – (noun), destructive force that breaks down rocks into smaller pieces

5. Weathering A destructive force that breaks down rocks. Two types:
Mechanical
Chemical

6. Mechanical Weathering
The breaking of larger rock into smaller rock called sediment
Ice – water goes into cracks of rocks, freezes, and breaks rock apart.
Moving air & Water – causes weakening of rock and it will crumble
Living things – plant roots and burrowing animals

7. Mechanical Weathering -
No change in the rock,
it just gets smaller!

8. Chemical Weathering Rocks change into other materials
Water is the main factor causing chemical weathering.
Water dissolves minerals that make up certain rock
Water dissolves certain chemicals from the air & soil to form a weak acid – which dissolves minerals

9. Often there is a
combination of
different types of
weathering at work.

10. Cave Formation Underground hollow areas created by weathering
Weak acids seep into the ground
Acid dissolves minerals in rock
Over time, holes produced in the rock
At first full of water, but eventually water drains

11. Limestone Many caves are made from limestone
The minerals in limestone is easily dissolved by weak acid

12. Describe three ways that mechanical weathering may occur?
Water in the cracks of rocks, freezes, and busts rock into smaller pieces
Wind or rushing water hitting rocks causes them to weaken and crumble.
Plant roots breaks apart rock.

13. Why do many caverns form in limestone?
The minerals in limestone are easily dissolved by acids.

14. Erosion
The carrying away of sediments by moving water, wind, or moving ice
Common agent of erosion: Water moving down a river

15. River Valley Formation
Begins as a shallow stream at higher elevation
Stream grows and carries sediment away
In time, the river cuts a V-shaped valley

16. Frozen Water Glaciers formed the rolling plains and the Great Lakes.
Glaciers move down stream toward the sea.
Move large amounts of rock & soil.
They form hallows in the land they erode. When they melt they form lakes.

17. Ocean waves & Currents
Crashing waves break down rock along coastlines.
Sediments are dragged back and forth, slowly turning into sand.
Wind & Waves erode the land.
Sea caves may join to form a sea arch.
Erosion may continue until arch falls creating a sea stack.

19. Weathering vs. Erosion Weathering
Process that breaks down rock into smaller pieces called sediment
Erosion
The carrying away of sediments by moving water, wind, or moving ice

20. Slow and Fast Changes Chemical weathering = takes thousands of years
But, after a cave is formed, the weight my be to great causing a sudden collapse which forms a sinkhole.

21. Sinkholes Form very suddenly
Land above weathered rock sinks into a hole.

22. Landslides Occur suddenly due to erosion
Large movements of land that tumble down a steep slope.
Mudslides, rock falls, & avalanches

23. Causes of landslides Gravity is the main cause
Erosion from rivers, rain, glaciers, or ocean water
These steepen the slope and loosen sediment
A disturbance, such as an earthquake, can shake the rocks loose.
Volcanoes can cause landslides also.

24. How are a sinkhole and a landslide alike? How are they different?
Occur quickly
Result of weathering & erosion
Gravity pulls sediment downward
DIFFERENT
Sinkhole is formed when rock above a cave falls into the cave
In a landslide, rocks and soil tumble down a hill.

25. What are the four forces that can combine to cause a landslide?
Erosion loosens sediments making a steep slope
Rain causes sediments to become heavy with water
Earthquakes shake the sediments loose
Gravity carries the sediments downhill

26. Turn to page C19 to answer the Review questions.

27. More
Review

28. Rocks break down during a destructive process called what?
weathering

29. This forms when agents of mechanical weathering break rocks into smaller pieces.
sediment

30. Wind, water, and moving ice move sediments during the process of ________.
erosion

31. The rocky outer layer of Earth’s surface is called the ________.
crust

32. A ______ map shows the shape of surface features and their elevations.
topographic

33. A flat landform found at a high elevation is called a ______.
plateau

34. Earth’s crust consists mostly of
A. glaciers
B. Pressurized metals
C. magma
D. Solid Rock

35. Earth’s crust consists mostly of
D. Solid Rock

36. List three causes of mechanical weathering.
Ice
Wind
Moving water
Plant & animal activity

37. Describe how chemical weathering can take place below Earth’s surface.
Water seeps into deep cracks and dissolves minerals in rock.
Acid rain seeps into cracks in rock and dissolves below the surface.

38. Wind, running water, and glaciers lead to erosion
Wind, running water, and glaciers lead to erosion. Which one moves sediments most quickly? Which moves sediments most slowly? Which is capable of moving the heaviest sediments?
Fast-flowing water & high speed winds can carry small sediments quickly.
Glaciers move most slowly, but are capable of carrying large amounts of sediment with them.

39. The End