1. Weathering & Soil

2. Weathering
WEATHERING: the process by which rocks are BROKEN down by the action of PHYSICAL or CHEMICAL processes.
2 Types of Weathering
1. MECHANICAL weathering: rocks are broken down into SMALLER pieces without being chemically changed. This is caused by several things.

3. Mechanical Weathering
Examples:
ICE:
FROST action – repeated freezing and thawing
ICE Wedging: frost action where WATER seeps into cracks during warm weather, then freezes, EXPANDS, and breaks rock during cold weather.

4. Mechanical Weathering
Examples
ABRASION: other rocks or sand rub and WEAR away other rocks
WIND - abrasion caused by the wind BLOWING sediments
WATER – abrasion caused by waves moving sediments
GRAVITY: abrasion caused by rocks falling on other rocks and from mountains and hills.

5. Mechanical Weathering
PLANTS: ROOTS get into cracks, grow, expand, and break rocks
ANIMALS: animals burrow & cause abrasion by BURROWING (digging)
Wetting and Drying - causes clay minerals to expand and contract, and salts may dissolve and re precipitate.
Sheet Joining - surface sheets of material fracture and exfoliate because of pressure release.
Exfoliation - The peeling of rounded thin layers from the rocks surface.

6. The rocks are essentially torn apart by physical force, rather than by chemical breakdown.

7. Chemical Weathering ACID RAIN: caused by PRECIPITATION (or pollution)\
CHEMICAL weathering : rocks broken down into smaller piece and are BROKEN DOWN by a CHEMICAL reaction.
WATER: (Hydrolysis) can chemically change rocks over millions of years
ACID RAIN: caused by PRECIPITATION (or pollution)\
ACIDS IN LIVING THINGS: ex: LICHENS produce acids that break down rock.
AIR- OXIDATION: OXYGEN in air reacts with iron in certain rocks to make RUST (oxide).
Carbon Dioxide mixes with rain water to form Carbonic Acid. It dissolves rock and caves form underground.
Sulfuric Acid is pollution from factories that dissolves in rainwater to weather metals and rocks.

8. Lichens produce acid that break down rock.

9. RATES OF WEATHERING How fast does weathering happen?
This depends on many things such as CLIMATE, elevation, and composition (what the rock is made of).

10. Rates of Weathering
DIFFERENTIAL WEATHERING: when SOFTER rocks wear away from the weather & leave the HARDER and more weather-resistant rocks behind (ex: Devil’s Tower – the softer part of the volcano is gone, but the harder rock is left behind.)
THE SHAPE OF THE ROCK: the MORE rock that is exposed, the MORE it will weather away.
CLIMATE:
Chemical weathering happens FASTER in warmer, HUMID climates
Mechanical weathering happens faster in COOLER climates where there is a lot of FREEZING & thawing
ELEVATION:
HIGHER rocks weather away faster because they are exposed to ICE, WIND & RAIN more
The steeper the SLOPE of the mountain, the faster the SEDIMENTS will flow downhill and the faster the ROCKS will weather away

11. Mechanical Weathering:
Devil’s Tower: the softer outer part of the volcano is gone, but the harder rock is left behind
Chemical Weathering:

12. SOIL
SOIL: a loose mixture of MINERAL fragments, ORGANIC material, water, & air that can support the growth of VEGETATION.
PARENT ROCK: a rock formation that was the SOURCE of soil

13. Soil HORIZONS (layers)
O, -humus (dark soil full of nutrients from decaying plants and animals)
A – topsoil
E- LEACHING occurs (water drains nutrients down)
B - collects NUTRIENTS from upper layers
C- a lot of WEATHERED bedrock—big chunks
R- bedrock

14. 2. Leaching:
1. Humus:

15. Soil Properties: 1. TEXTURE: size of the sediments
SAND: has the LARGEST grains and water moves through it easily
SILT: medium sized grain
CLAY: smallest grains and WATER does not move through easily

16. Soil Properties
2. STRUCTURE: soil sediments can CLUMP in some areas and be loose in other areas
3. SOIL FERTILITY: the soil’s ability to SUPPORT plant growth- Humus is great for this

17. Soil Properties
4. TEMPERATURE: plants can’t GROW if the soil temperature is too high or too LOW
5. MOISTURE: depends on the soil’s texture

18. Soil Properties
6. pH: influences which nutrients will be available to plants

19. Soil Properties 7. Color:
the DARKER the soil, the more organic and FERTILE
reddish & yellow contain IRON, but are also fertile
whitish contain SALTS & are not fertile for farming crops

20. Soil & Climate
TROPICAL RAIN FOREST SOIL: not very fertile, too much LEACHING (water) from heavy rain, & too many PLANTS soak up nutrients
DESERT SOIL: little RAIN, so little weathering occurs, but no rain to wash away SALTS
TEMPERATE FOREST SOIL: BEST for crops & weathering
ARCTIC SOIL: little water & COLD temperatures so there is little decomposition to provide nutrients

21. SOIL CONSERVATION
A method to PROTECT soil from EROSION & nutrient loss
WHY DO WE NEED SOIL?
For plant growth, for decomposers to live in

22. Ways to Prevent Soil Erosion
CONTOUR Plowing:
planting ROWS of crops across HILLS instead of up & down to hold soil in place
Minnesota." Online Photograph. Britannica Student Encyclopædia. 3  Oct.  2008  <

23. WAYS TO PREVENT SOIL EROSION
2. Terracing: changing a steep slope into a series of FLAT stairs to plant crops on

24. Ways to Prevent Soil Erosion
3. NO-TILL Farming: leaving old, HARVESTED plants lay on the top of the field to hold soil down

25. Ways to Prevent Nutrient Loss:
Crop ROTATION:
planting crops in DIFFERENT fields each year so that the NUTRIENTS of one field are not used up right away

26. Ways to Restore Nutrients to the Soil:
COVER Crops:
crops are planted in-between HARVESTS to replace nutrients & cover the GROUND to prevent erosion from wind & rain