Weathering


 * Weathering-** The breakdown of rocks at or near the surface of the earth.
 * Physical Weathering**- the breakdown of rock into smaller pieces without chemical change.
 * Ice Wedging (frost action)**- Water held in the cracks of rocks wedges the rock apart when it freezes.
 * Root Wedging (plant action)**- Tiny roots grow into cracks in the rock and then as the root grows the rock splits. [[image:treeroot3.jpg]]


 * Exfoliation-** when large masses of rock, mainly igneous, are lifted up to the surface the relief of overlying pressure causes the rock to expand. Upward expansion leads to curved breaks which may peel off in layers
 * Chemical Weathering-** The breakdown of rock through a change in mineral or chemical composition.
 * Oxidation-** The chemical reaction of oxygen with other substances. Iron is most easily attacked resulting in rust (iron oxides)
 * Carbonic Acid-** When carbon dioxide dissolves many common minerals.

allow them to weather at different rates. • Quartz- almost unchanged by chemical weathering. It is hard and does not have cleavage so it also resists mechanical weathering. • Feldspar, Mica, Calcite, and Gypsum- affected by both types of weathering and will break down into clay with calcite and gypsum dissolving and being carried off in solution.
 * Minerals Resistance to Weathering-** Different minerals and rocks have different physical and chemical properties which

• Shale- is the least resistant to mechanical weathering • Sandstone- is the most resistant to mechanical weathering - The type of cement which holds the sandstone together determines how resistance the rock is **Calcite- low resistance** and **Silica- high resistance.** **Factors Affecting Rate of Weathering!** Exposure- the closer to the surface of the earth, the faster it will weather. - Rate and type of weathering depends on exposure of rocks to air, water and the action of living things. Two samples of the same material having the same mass can have different surface areas. If one sample is a large piece of marble with a mass of 50g, and the other is 50g of many small pieces of marble. The smaller size pieces will have the greater surface area. Climate effect on Weathering. Chemical weathering**- is usually greater in warm, moist climates.** Physical Weathering**- usually greater in moist areas with temperature variations (cold and warm)**
 * Sedimentary Rocks-**
 * -**Rocks which contain the mineral calcite, such as //Limestone// or //Marble// are somewhat resistant to mechanical weathering but is the **least resistance to chemical weathering.**
 * Surface Area-** The greater surface area exposed to the weathering the faster the rate of weathering.

2) May contain soluble minerals, such as calcium and magnesium carbonates 3) color is usually red- brown from iron oxides that form above and wash down
 * Soils**- soil is made of loose, weathered rock and organic material in which plants with root can grow. The rock material is composed sand, silt, and clay.
 * Parent material-** the material from which a soil is formed.
 * Residual Soil-** soil that has the bedrock beneath the soil as a parent material
 * Transported Soil-** soild formed from deposits left by winds, rivers, and glaciers.
 * A-Horizaon (Top Soil)-** darkest color due to organic material.
 * B-Horizaon (Subsoil)-** 1) clay is washed to the subsoil
 * C-Horizon**- Made of slightly weathered parent material (rock fragments)

UN-WEATHERED BEDROCKS

Climate Tropic soils from in areas with high temperatures and heave rainfall. A thick infertile soil profile is results of heavy rain

Grassland soils from areas with enough rainfall for the heavy grass, but not trees/ About 1 meter thick and fertile

Forest soils form in humid regions with cool seasons. Soil profile is less then 1 meter thick with the developed A, B, and C Horizon

Desert soil form in very dry climates. Soil profile is a few centimeters