2 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.
3 Mechanical Weathering Examples:ICE:FROST action – repeated freezing and thawingICE Wedging: frost action where WATER seeps into cracks during warm weather, then freezes, EXPANDS, and breaks rock during cold weather.
4 Mechanical Weathering ExamplesABRASION: other rocks or sand rub and WEAR away other rocksWIND - abrasion caused by the wind BLOWING sedimentsWATER – abrasion caused by waves moving sedimentsGRAVITY: 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 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.
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 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.
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 WeatheringDIFFERENTIAL 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 climatesMechanical weathering happens faster in COOLER climates where there is a lot of FREEZING & thawingELEVATION: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
11 Mechanical Weathering: Devil’s Tower: the softer outer part of the volcano is gone, but the harder rock is left behindChemical Weathering:
12 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
13 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 bedrock—big chunksR- bedrock
15 Soil Properties: 1. TEXTURE: size of the sediments SAND: has the LARGEST grains and water moves through it easilySILT: medium sized grainCLAY: smallest grains and WATER does not move through easily
16 Soil Properties2. STRUCTURE: soil sediments can CLUMP in some areas and be loose in other areas3. SOIL FERTILITY: the soil’s ability to SUPPORT plant growth- Humus is great for this
17 Soil Properties4. TEMPERATURE: plants can’t GROW if the soil temperature is too high or too LOW5. MOISTURE: depends on the soil’s texture
18 Soil Properties6. pH: influences which nutrients will be available to plants
19 Soil Properties 7. Color: the DARKER the soil, the more organic and FERTILEreddish & yellow contain IRON, but are also fertilewhitish contain SALTS & are not fertile for farming crops
20 Soil & ClimateTROPICAL RAIN FOREST SOIL: not very fertile, too much LEACHING (water) from heavy rain, & too many PLANTS soak up nutrientsDESERT SOIL: little RAIN, so little weathering occurs, but no rain to wash away SALTSTEMPERATE FOREST SOIL: BEST for crops & weatheringARCTIC SOIL: little water & COLD temperatures so there is little decomposition to provide nutrients
21 SOIL CONSERVATIONA method to PROTECT soil from EROSION & nutrient lossWHY 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 placeMinnesota." 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