Weathering and Soil Formation
Notes
Weathering
• Two types
– Mechanical Weathering
• Ice
• Abrasion
• Wind, Water, Gravity
• Plants
• Animals
Chemical Weathering
Water
Acid precipitation
Air
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 soilsand, 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 soil
Soil 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