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 CO2 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 http://quashnick.net/blog/media/1/20111025-Soil_Pyramid.gif

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 and 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, more vegetation