Weathering & Soil

Weathering & Soil WeatheringWEATHERING: the process by which rocks are BROKEN down by the action of PHYSICAL or CHEMICAL processes. 2 Types of Weathering1. MECHANICAL weathering: rocks are broken down into SMALLER pieces without being chemically changed. This is caused by several things.

Mechanical WeatheringExamples: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.

Mechanical WeatheringExamples

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.

Mechanical WeatheringPLANTS: ROOTS get into cracks, grow, expand, and break rocksANIMALS: 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.

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

Chemical WeatheringCHEMICAL weathering : rocks broken down into smaller piece and are BROKEN DOWN by a CHEMICAL reaction. WATER: (Hydrolysis) can chemically change rocks over millions of yearsACID 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.

Lichens produce acid that break down rock.

RATES OF WEATHERINGHow fast does weathering happen?

This depends on many things such as CLIMATE, elevation, and composition (what the rock is made of).

Rates of WeatheringDIFFERENTIAL WEATHERING: when SOFTER rocks wear away from the weather & leave the HARDER and more weather-resistant rocks behind (ex: Devils 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 climatesMechanical 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 moreThe steeper the SLOPE of the mountain, the faster the SEDIMENTS will flow downhill and the faster the ROCKS will weather away

Chemical Weathering:

Mechanical Weathering:

Devils Tower: the softer outer part of the volcano is gone, but the harder rock is left behind

SOILSOIL: 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

Soil HORIZONS (layers)

O, -humus (dark soil full of nutrients from decaying plants and animals)A topsoilE- LEACHING occurs (water drains nutrients down)B - collects NUTRIENTS from upper layersC- a lot of WEATHERED bedrockbig chunksR- bedrock

1. Humus:

2. Leaching: Soil Properties:1. TEXTURE: size of the sedimentsSAND: has the LARGEST grains and water moves through it easilySILT: medium sized grainCLAY: smallest grains and WATER does not move through easily

http://www.iconn.org/presentations/CECA_Fall2007/Roche_files/slide0074_image027.jpgSoil Properties2. STRUCTURE: soil sediments can CLUMP in some areas and be loose in other areas

3. SOIL FERTILITY: the soils ability to SUPPORT plant growth- Humus is great for this

Soil Properties4. TEMPERATURE: plants cant GROW if the soil temperature is too high or too LOW

5. MOISTURE: depends on the soils texture

Soil Properties6. pH: influences which nutrients will be available to plants

http://www.worsleyschool.net/science/files/pH/phscale.gifSoil Properties7. 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

http://climatelab.org/@api/deki/files/190/=Biochar_dark_soil_betchkal.jpg

http://eusoils.jrc.ec.europa.eu/projects/soil_atlas/images/1-39%2028_img_2.jpg

http://www.wunderground.com/data/wximagenew/m/MikeTheiss/140.jpgSoil & ClimateTROPICAL 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

SOIL CONSERVATIONA method to PROTECT soil from EROSION & nutrient loss

WHY DO WE NEED SOIL? For plant growth, for decomposers to live in

Ways to Prevent Soil ErosionCONTOUR Plowing: planting ROWS of crops across HILLS instead of up & down to hold soil in place

Minnesota." Online Photograph. Britannica Student Encyclopdia. 3 Oct. 2008 . WAYS TO PREVENT SOIL EROSION2. Terracing: changing a steep slope into a series of FLAT stairs to plant crops on

http://en.wikipedia.org/wiki/Image:Rice_terraces.pngWays to Prevent Soil Erosion3. NO-TILL Farming: leaving old, HARVESTED plants lay on the top of the field to hold soil down

http://whyfiles.org/241GM_2/index.php?g=3.txt

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

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