Weathering and Soil Formation

Notes

Weathering

• Two types– Mechanical Weathering

• Ice• Abrasion• Wind, Water, Gravity• Plants• AnimalsChemical Weathering

WaterAcid precipitationAir

Weathering

• Acid Precipitation– Precipitation is naturally acidic, but acid pre.

Contains higher levels– High amounts can weather rocks quickly– Can be caused by acids from natural sources like

volcanos or caused from pollution from burning fossil fuels

– Form gases which when combined with water in the atmosphere form weak acids that fall back to the ground as rain or snow

Weathering

• PH scale slide

Rates of Weathering

• Differential weathering- process where less resistant rocks are replaced with harder more resistant rocks

• Shape-large rock will take more time to weather, but if it is broken down by weathering then each piece will take less time.

Rates of Weathering

• Climate- average weathering condition over a long period of time.

• **Mailbox example pg 286• Temperature and water can both play a big part

in weathering- water can cause ice wedging and temperature can cause freezing and thawing

• Elevation- steepness of mountain slopes can increase weathering

From Bedrock to Soil

• Soil- loose mixture of small mineral fragments.• Parent rock is the source of rock fragments in

soil- one rock is crushed• Bedrock is parent rock because the soil formed

above it came from the bedrock below• Soil that remains above its parent rock is

residual soil• Soil that can be blown or washed away from

parent rock is called transported soil

From Bedrock to Soil

• Soil Properties– Soil texture: soil quality based on proportions of soil-

sand, silt, and clay– Soil structure: arrangement of soil particles. Not

always even– Soil fertility: soils ability to hold nutrients and supply

nutrients to plants. Other nutrients come from humus (organic material formed in soil)

– Soil horizons: layers of soil- from topsoil to bedrock– Soil PH: influences how nutrients dissolve in the soil

From Bedrock to Soil

• Soil and Climates– Tropical Rain Forest Climate- humid and rainy– Desert Climates- low precipitation, low rate of

weathering= less soil– Temperate Forest and Grassland Climates- most of

U.S has temperate climate. – Arctic climate- “cold desert” slow formation of soil

Soil Conservation

• Soil Conservation- maintain the fertility of soil by protecting soil from erosion and nutrient loss.

• Importance– Soil provides nutrients to plants- without soil- no

healthy plants– Animals get energy from plants– Housing for animals – Water storage

Soil Conservation

• Soil Damage and Loss- can lead to soil loss – Soil erosion- when left unprotected it can be exposed to

erosion which moves soilSoil Conservation techniques

Contour plowing and terracing- to prevent erosion- a farmer could plow across the slope of the hills. Terracing changes one steep field into a series of flatter fields

Cover crop and crop rotation- cover crops are when another crop is planted in place of the previous crop of a different season to restore nutrients to soil. Crop rotation is when some crops are rotated during seasons