1. Weathering

2. Weathering: the physical and chemical breakdown of rocks into smaller particles called sediments.
When Rocks are exposed to:
Air
Water
Pressure changes
Actions of living things
Can also affect structures such as buildings and roads

3. Physical Weathering Breaking a rock by force
The smaller pieces of rock have the same composition as the rock they came from.
Ex: hitting, scratching, cracking

4. Causes of Physical Weathering
Freezing & Thawing (ice wedging):
Water seeps into cracks in rocks and freezes when the temperature drops.
Water expands when it freezes.
With repeated freezing and thawing, the cracks expand until pieces of the rock break off.

5. Ice Wedging
Happens the most in areas where the temperature swings above and below freezing

6. Causes of Physical Weathering
Release of Pressure (exfoliation): a release of pressure can cause outside layers of a rock to crack and flake off like an onion
Ex: rocks removed by humans in mining; erosion; glaciers melt

7. Causes of Physical Weathering
3. Plant Growth: roots of plants can enter tiny cracks in rock and force the cracks further apart.

9. Causes of Physical Weathering
4. Abrasion: occurs when sediments carried by streams, wind, glaciers, or gravity cause the particles to collide into each other and the surrounding rock.
The characteristic rounded shape of rocks from river beds and beaches is caused by abrasion.

13. Causes of Chemical Weathering
Rock material is changed into another substance by reacting with a chemical.
Causes of Chemical Weathering
1. Carbon Dioxide: dissolves in rainwater to form carbonic acid.
- Carbonic acid in surface water and ground water easily dissolves some rocks
Limestone, marble, calcite

14. Caves form as a result of carbonic acid weathering rock

15. Sinkholes formed as a result of chemical weathering

16. Limestone bedrock

17. Carbonic acid rain water seeps into the limestone bedrock through the cracks. This water dissolves the limestone rock.

18. Sinkholes
Columns
Stalactites
Stalagmites

19. Causes of Chemical Weathering
2. Water: weathers rock by DISSOLVING it. - most important cause of chemical weathering
For example, granite is very stable in cool dry climates, but in moist climates rainfall dissolves much of the mineral feldspar.
The feldspar becomes clay, which is too weak to keep the rock from breaking apart. The mineral quartz remains behind as sand.
Weathering Granite

20. Causes of Chemical Weathering
3. Oxygen: oxygen in the air can combine with minerals in a rock.
For example, when oxygen combines with iron minerals, iron oxide (RUST) forms.
The chemical change of the mineral weakens the rock and the rock crumbles.

21. Causes of Chemical Weathering
4. Living Organisms: plants can produce acids that chemically breakdown rock.
Lichens chemically weathering a fallen tree
Lichens and mosses

22. Causes of Chemical Weathering
Man-made Acids – Gases produced by humans can dissolve in the water droplets of a cloud to produce acid rain.
H2SO4 – sulfuric acid
HNO3 – nitric acid

23. Acid Rain formation

25. What affects the RATE of weathering?
1. Type of Rock: some minerals break down more easily than others.

28. What affects the RATE of weathering?
2. Climate: weathering occurs FASTER in locations with wet climates.

29. Due to climate and different weathering processes, landscapes develop differently.
Arid climate
Humid climate

30. What affects the RATE of weathering?
3. Particle Size: Weathering takes place on the outside surface of rocks.
The more surface area that is exposed to weathering, the faster the rock will be broken down.
As a rock breaks into smaller pieces, the surface area increases, therefore the rate of weathering increases.

31. A full solid block has the least surface area
A full solid block has the least surface area. The interior is safe from exposure.
A smashed piece has the greatest surface area exposed. The interior can now be attacked.

32. What affects the RATE of weathering?
Exposure: the closer a rock is to the surface, the faster it will weather.
Weathering is dependent on exposure to air, water, and actions of living things

33. Soil Formation
Soil is a combination of weathered rock and organic matter.
Humus = decayed plant and animal material found in soil. Soil that contains 20-30% humus is considered rich soil for plant growth.

34. Soil Development
TIME
1. The surface of the rock gets attacked by weather and broken into smaller pieces
2. Over many years, you wind up with heavily weathered sediments at the surface.
3. As you dig deeper, you find less and less weathering and the materials become coarser.

35. Soil Layers
1. Topsoil or A Horizon = the top layer of soil that contains more humus than the layers below.
2. Sub soil or B Horizon = consists of clays and dissolved minerals that have been washed down from above. Contains less humus.
3. C Horizon = consists of weathered rock fragments, usually from the parent rock below.
4. Bedrock = the layer of rock beneath the soil. Frequently the parent rock of the soil above.

36. Residual vs. Transported Soil
If the bedrock matches the rock fragments in the soil, the soil is most likely residual.
If it does not, the soil is most likely transported from another location.
Most soil on Earth’s surface is transported.
Residual – soil will have some characteristics of the parent material from which it formed.
Transported – by wind, glaciers, running water. NYS Soils were transported by glacier (and its meltwater) 10 – years ago