Weathering and Erosion

Soil formation

Standards

• S6E5, S6CS2,

• S6CS3, S6CS4,

• S6CS5, S6CS6

• S6E3, S6E5, S6CS2,

• S6CS3, S6CS4,

• S6CS6, S6CS10

Weathering

• 2 types

–Mechanical

–Chemical

Effects of rock type

• Hardness of rock determines weathering rate

• Chemicals in air – air pollution

• Amount of water in air

• Temperature of area

Mechanical Weathering

• When rocks are broken apart by physical processes

• Chemical makeup of rock stays the same

• Pressure release

–Under Earth’s surface

–Rock layers break apart

–Exfoliation

•Layers slowly break off

Plants and animals

• Water and nutrients collect in cracks and soil

• Plants grow in cracks

• Animals burrow and leave tunnels and holes in ground

Ice wedging

• Water enters cracks in rock and freeze.

• Expanding water causes rock to break apart

• Ice melts and processes repeat.

• Abrasion

–Wearing down by friction

–Moving water (river)

–Rocks hitting each other

–Ocean waves

Chemical weathering

• Chemical reactions dissolve the minerals in rocks or change them into different minerals

• Weakens rock

• Dissolving

–Water + carbon dioxide

–Dissolves rock into new substance

• Rusting–Iron in soil

–Oxygen rusts iron

–Soil is red in color

Natural Acids

• Water mixes with carbon dioxide gas and form carbonic acid

• Roots and decaying plants give off acids

• Dissolve minerals in rock

Effects of Climate

• Pattern of weather that occur in a particular area over a period of time

• Cold areas – mechanical weathering – ice wedging

• Warm areas – chemical weathering – rain

Surface area

• Small pieces of rock have more surface area exposed than large rock

• Allows more rock to be exposed and weathering to occur

4.2 Weathering and organic soil formation

1. Climate

2. Slope of land

3. Type of rock

4. Type of vegetation

5. Amount of time rock has been weathering

Composition of Soil

• Rock sediment

• Minerals

• Organic plant matter

• Decayed animals

• Microorganisms – bacteria

• Humus – decayed organisms

• water

Soil horizons

• Horizon A – top layer of soil – litter of leaves twigs and other organic material – litter prevents erosion – topsoil – dark and fertile

• Horizon B – below A – lighter in color – no litter – less fertile – leaching – removal of dissolved minerals – move from A to B

• Horizon C - bottom layer – thickest layer- not much organic matter-not fertile – many rocks

Soil types

• Type of soil determined – Climate– Region– Rainfall– Types of rock

Observable properties of soil

• Texture

• Color

• Pore space

• Chemistry

Human activities affect soil

Land-use

• Farming– Overgrazing of animals=desertification– Adding nutrients (organic or artificial)– Top soil erosion– Clear trees– Wind

Construction and development

• Roads

• Houses

• Malls

• Stores

• What are some problems with this?

Mining

• How would this affect an area?

Protection of soil

• Crop-rotation

• Conservation tillage

• Terraces

• Contour plowing

• Windbreaks

Contour plowing

Crop-rotation

Windbreaks

Preventing Soil Erosion

• Managing crops• Plant shelter belts – protect soil from wind• Proper grazing management – arid areas

farmers do not plow under vegetation – allow grazing of natural vegetation

• “No-till” farming –– stalks are left as ground cover during the winter. – Farmers seed area without plowing. – Leftover stalks stop erosion, keep moisture in ground

and control weeds.

Reduce erosion at construction sites

• Cover cleared areas with mulch, mats, or plastic coverings

• Water sprayed onto cleared area • New topsoil is added to exposed areas• Area is seeded and reinforced with netting

or straws • Retaining walls are built for steeper areas

– made of stone, concrete or wood