WEATHERING PHYSICAL WEATHERING Process by which rocks and
WEATHERING
PHYSICAL WEATHERING: Process by which rocks and minerals break down into smaller pieces • Temperature (freeze/thaw) • Pressure
CHEMICAL WEATHERING: Process by which rocks and minerals break down as a result of a chemical reaction
CHEMICAL WEATHERING: • Water – the reaction of water with other substances is known as hydrolysis (decomposition of minerals)
CHEMICAL WEATHERING: • Oxygen – chemical reaction where oxygen combines with other substances is called oxidation (ex. Iron)
CHEMICAL WEATHERING: • Carbon dioxide – when CO 2 combines with water in the atmosphere, it forms a weak carbonic acid • Forms clay minerals
CHEMICAL WEATHERING: • Acid rain – caused by oxidation of sulfur dioxide and nitrogen oxides that are released into the atmosphere by human activities
THE RATE OF WEATHERING IS AFFECTED BY: 1. Climate – rain, temperature and evaporation • Chemical weathering = warm temps, abundant rainfall, lush vegetation • Physical (mechanical) weathering = cooler, dryer climates
THE RATE OF WEATHERING IS AFFECTED BY: 2. Rock Type – resistance to being broken down. Some rocks are stronger than others
THE RATE OF WEATHERING IS AFFECTED BY: 3. Topography – slopes vs. level areas (gravity)
SOIL PROPERTIES • Soil is made of a mixture of weathered rock particles and organic material. – Humus: plant or animal material; dark colored. – Most organic matter in soil comes from plants!
Soil is mostly sand, clay or silt particles
SOIL TEXTURE IS DETERMINED BY PARTICLE SIZE
SOIL TEXTURE IS DETERMINED BY PARTICLE SIZE • Clay: smallest particle size (less than. 002 mm); – Sticky, moldable – Least permeable, low porosity – Susceptible to runoff
SOIL TEXTURE IS DETERMINED BY PARTICLE SIZE • Silt: Medium particle size (. 002 mm -. 06 mm); ’ – Crumbly – Less permeable, medium porosity – often found around river banks, river beds or lake beds.
SOIL TEXTURE IS DETERMINED BY PARTICLE SIZE • Sand: largest particle size (. 06 mm – 2 mm); – Loose, gritty – Very permeable, high porosity – weathered from rocks containing quartz.
SOIL TEXTURE TRIANGLE • A soil triangle is used to determine the texture of a sample of soil
What is the name of soil that is: - 30 % Clay - 50 % Silt - 20% Sand What is the name of soil that is: - 20 % Clay - 40 % Silt - 40% Sand
SOIL PROFILE • Cross section in which layers (a. k. a. horizons) of soil and bedrock can be seen
SOIL HORIZONS • O horizon: organic material • A horizon: consists of topsoil (mostly sand some clay) • B horizon: subsoil reddish brown in color; made mostly of clay; rich in minerals and nutrients • C horizon: deepest layer; consists of broken and solid, unweathered bedrock. (parent material)
SOIL FERTILITY • Soil fertility is a measure of how well a soil can support the growth of plants
SOIL FERTILITY • Factors that affect soil fertility: – Minerals and nutrients present – Microorganisms present – Amount of precipitation – Topography* – Level of acidity
SOIL FERTILITY • Topography – The topography of a region affects the thickness of the soil – Soil on slopes = more erosion, thinner soil – South-facing slopes = more sunlight,
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