1. Weathering
Weathering is the name given to processes that change the surface material of the Earth as a result of exposure to the effects of water and the atmosphere

2. The two types of weathering are:
physical weathering
chemical weathering

3. Physical weathering
Physical weathering (also known as mechanical weathering) is the process by which rocks are broken down into smaller fragments without undergoing any change in chemical composition.
Physical weathering is mainly caused by the freezing of water, the expansion of rock, and the activities of plants and animals.

4. Agents of physical weathering
Frost wedging
Exfoliation
Animals and plants
Root wedging

5. Frost Wedging rocks are weathered by the action of freezing water
rainwater, melted snow, or ice trickles into cracks in the rocks. When the temperature falls below the freezing point of water, the water trapped inside the rock changes into ice.
When water freezes, it increases in volume. This expansion causes the crack to increase in size

6. Exfoliation.
Rock formed deep underground (under great pressure) becomes exposed at the Earth's surface
The release of overlying pressure causes the newly exposed bedrock to expand, forming cracks parallel to the surface.
Then, frost wedging causes large, curved slabs of rock to peel away from the main body of the rock
The peeling away of the outer layers from a rock is called exfoliation.

7. Animals and Plants
Insects, earthworms, rabbits, woodchucks, and many other animals burrow through the soil.
The act of burrowing through soil helps to break down rock particles into smaller and smaller pieces.

8. Root Wedging
You may have seen trees that appear to be growing out of solid rock. Trees occasional grow in soil that has collected in small cracks in the bedrock. In other cases trees grow in soil in the cracks of a boulder.
The pressure exerted by the roots cause the rock to split apart even wider.

9. Chemical weathering
Exposure to air, water, and organisms can change the minerals in a rock into new substances that have different chemical compositions.
These new substances are generally softer or weaker than the original materials, so they tend to cause the rock to crumble and fall apart. The breaking down of rocks through changes in their chemical composition is called chemical weathering.

10. An example of chemical weathering is the change of feldspar in granite to clay. When acted upon by water, the feldspar changes into powdery clay minerals. Feldspar and clay have different chemical compositions.

11. Agents of chemical weathering
Acids
Water
Oxygen
Carbon dioxide

12. Acids
Lichens "eat" rocks by releasing acids that slowly dissolve the minerals in the rocks. In addition, the action of bacteria and other microscopic organisms on dead plants and animals changes the composition of their remains. As these changes take place, acids are produced. The acids then dissolve the minerals in the rocks, and the rocks crumble apart.

13. Water
When water comes into contact with certain minerals the water combines chemically with these minerals and changes them. This kind of chemical weathering is called hydrolysis.

14. Oxygen
Iron, in the presence of moisture, combines chemically with oxygen in the atmosphere. The combining of oxygen with another substance is called oxidation. The oxidation of an iron nail produces a powdery reddish brown substance called rust.
Oxidation also takes place in rocks that contain iron-bearing minerals.

15. Carbon Dioxide
When carbon dioxide and water combine chemically, they form a weak acid called carbonic acid (H2CO3).
carbonic acid dissolves calcite from rocks slowly.
The world's largest underground caverns were formed by this type of chemical weathering.

16. The ability of a rock to resist weathering depends mainly on the mineral composition of the rock and on the number of cracks in the rock.

17. Soil formation
As rock weathers into smaller and smaller fragments, plants begin to grow in the weathered rock. Then worms, insects, bacteria, and fungi begin living among the plant roots. These organisms don't just live in the weathered rock they help it evolve into soil by adding organic matter.

18. Soil formation
When the plants and animals that live in the soil eventually die, they break down in a process called decay. The dark-colored organic matter made of pieces of decaying plants and animals is called humus. As worms and insects burrow throughout the soil, they mix the humus with the fragments of rock. As you can see, weathered rock is constantly evolving into soil.

19. Have you ever ridden your bike by a river just after a heavy rain
Have you ever ridden your bike by a river just after a heavy rain? The water was so muddy that it looked like chocolate milk. Where do you suppose all of the mud came from?

20. Erosion
Erosion means the removal or transportation of material from one position on the surface of the Earth to a different position, again by the effects of water and the atmosphere.

21. The four major agents of erosion are:
Gravity
Wind
running water
glaciers.

22. Erosion caused by gravity
Gravity causes loose materials to move down slope. When gravity alone causes materials to move down slope, it's called mass movement.
Following are different types of mass movements

23. I. Slump. A slump is a type of mass movement that takes place on steep slopes. It occurs when loose materials or rock layers slip downward as one large mass. The material does not travel very fast or very far, but when it happens, a curved scar is left where the slumped material originally rested

24. Creep
Creep gets its name from the way sediments slowly creep down a hill. It is especially common in areas where freezing and thawing occur.
Small sediments are pushed up by the expanding water in the soil as the ground freezes. When the soil thaws the sediments
fall down slope.
Several years of soil creeping down slope can cause objects such as
utility poles and
fence posts to lean

25. Rockslides.
A rockslide happens when large blocks of rock break loose from steep slopes and tumble quickly to the bottom.
Rockslides commonly occur in mountainous areas. They happen most often after heavy rains or during earthquakes.
But they can happen on any rocky slope at any time without warning.

26. Mudflows
Mudflows usually occur in relatively dry areas where weathering forms thick layers of dry sediments. When heavy rains fall in these areas, the water mixes with the sediments and forms a thick, pasty substance. Gravity causes this mass to slide downhill.

27. Erosion caused by wind
The wind changes the landscape by moving sand, silt, and clay from one place to another.
Lightweight silt and clay particles can be lifted and carried by light breezes. This type of erosion is deflation
Flying sand grains erode pebbles, boulders, and even large rock outcrops by wind abrasion
During wind abrasion, flying sand grains sandblast, or chip away, any solid surface that they are blown against.

28. Loss of Topsoil. A long drought in the 1930s led to wind erosion of the fertile topsoil of the Plains states. Crops withered and died, leaving bare fields unprotected from the wind. Moist topsoil turned into powdery dust and farmers were helpless as the wind stripped the precious topsoil from their fields. On several occasions, strong winds carried thick clouds of dust-like topsoil from the Great Plains to the Atlantic Ocean—over 3000 km away. Because of the disastrous loss of topsoil during such dust storms, the region from Texas to South Dakota was called the "Dust Bowl."

29. RUNNING WATER The most important agent of erosion is running water.
When rain falls on sloping land, the runoff water flowing downhill carries away loose rock fragments and soil.
When water erodes without being in a stream channel, sheet erosion takes place.
small channels called rills, might be created by this flowing water.
If water continues to flow along the same path a gulley (deeper channels)may form.
Eventually streams are formed.

30. Glaciers moving mass of ice and snow is a glacier.
U-Shaped valleys are formed.
As they move over land, glaciers act like bulldozers, pushing any loose materials out of their path.