Weathering
Weathering is the process by which rocks on or near Earth s surface break down and change. Spherical weathering near Paris, NC
The two types of weathering are Chemical and. Mechanical
Mechanical Weathering
Mechanical weathering occurs when a rock is physically broken into smaller pieces. It may also be called Physical Weathering and does not involve any change in a rock s. Composition Changes are only in the size and sometimes the shape of the rock. Rocks and minerals break down into smaller pieces. There are 5 types of mechanical weathering: temperature & frost wedging, pressure, organic activity, gravity, and abrasion.
Temperature plays a significant role in mechanical weathering through heating and cooling. During the day rocks are heated up and the outer layers begin to expand. The inside of the rock however remains cool and does not expand. At night the outer layer contracts when cooled. This cycle can cause pieces of the rock to crack or flake off.
Ice wedging Water may get into cracks in the rock. Expands When water freezes, it expands by 9%. When the water freezes and expands, the surrounding rock may be broken apart.
The next time water freezes in the cracks the rock will be broken apart even further. Frost Wedging is the repeated thawing and freezing of water in the cracks of rocks. This is how potholes are formed.
Pressure Bedrock at great depths is under from the overlying rock layers. When the overlying layers are removed the pressure of bedrock is reduced. The bedrock surface is then able to expand.
Joints are long, curved cracks that may occur parallel to the surface of the rock. Over time when the outer rock layers are stripped away it is called exfoliation.
Wind-blown sand wears away rocks in a process called abrasion. Mars; polished rock due to wind abrasion
Animals burrowing may also loosen rock material.
Organic activity: Plants and animals can cause mechanical weathering. The roots of trees and other plants can wedge themselves into the cracks of rocks. As the roots grow, pressure is exerted on the surrounding rock and the rock will begin to split. This is called root pry.
Sometimes gravity pulls loosened rocks down mountain cliffs in a landslide, causing them to break apart
Chemical Weathering
The process by which rocks and minerals undergo changes in their composition as the result of chemical reactions is called chemical weathering There are 5 types: Water, oxidation, carbonation, acid precipitation, and plant acids.
An example of this would be the decomposition of a silicate mineral such as potassium feldspar into kaolinite. Water is the most important agent. The reaction of water with other substances is known as hydrolysis.
Oxygen in the air can combine with iron and through oxidation may form rust. An example would be when the iron in magnetite combines with atmospheric oxygen to form the iron in hematite. Example: 2Fe3O4 (magnetite) + ½ O2 --à 3Fe2O3 (hematite)
Carbonic acid is formed when carbon dioxide (CO2) combines with water in the atmosphere. That then falls to the Earth s surface as precipitation. (acid rain) This acid reacts with minerals such as limestone or marble and breaks them down.
Grandfather Mt. NC The oxidation of sulfur dioxide and nitrogen oxides that are released into the atmosphere may form acid rain.
The sulfur dioxide forms from the burning of fossil fuels and the nitrogen oxides are emitted from motor-vehicle exhaust.
The ph of water is neutral and has a value of seven(7).
Plants produce weak acids that can dissolve certain minerals in rocks. The acids seep into rocks and dissolve some of the minerals and the rock will begin to break apart. Lichens and mosses are examples
Rate of Weathering
The warmer and wetter the climate, the faster chemical weathering can occur. Dry, cool climates promote mechanical weathering.
In general, sedimentary rocks are more easily weathered than the harder igneous and metamorphic rocks.
20. The more total surface area available, the easier it is for a rock to be chemically weathered.
Section Assessment 1. Match the following terms with their definitions. weathering frost wedging exfoliation hydrolysis A. the process by which rocks on Earth s surface break down and change B. the process by which outer rock layers are stripped away C. the repeated freezing and thawing of water in the cracks of rocks D. the reaction of water with other substances
Section Assessment 2. What is the difference between mechanical and chemical weathering in relation to rock composition?
Section Assessment 3. Identify whether the following statements are true or false. Acid precipitation has a ph lower than 5.6. Hydrolysis can result in the formation of clay minerals. The highest rate of chemical weathering occurs in higher latitudes. Trees can play a part in physical weathering. Iron is not affected by oxidation.
What is Erosion? Erosion is defined as removal of rocks and soil by wind, water, ice and gravity. Wind, water, ice and gravity are also known as the agents of erosion.
Wind Erosion Wind can play a role by carrying material (especially sand and clay) from one place to another. As the wind blows, it picks up small particles of sand/sediment and blasts large rocks with the sand/sediment, cutting and shaping the rock.
Wind Erosion The intensity of wind erosion is determined by: Sum (amount of sand) Speed Slope Surface
Wind Erosion
Water Erosion When rain falls to the Earth it can evaporate, sink into the ground, or flow over the land as Runoff. When it flows over land, erosion occurs. Runoff picks up pieces of rock and "runs" downhill cutting tiny grooves (called rills) into the land.
Water Erosion How much erosion takes place is determined by the: Sum (amount of water) Slope Speed Surface
Water Erosion
Gravity Erosion Gravity Erosion is better known as Mass Movement and is defined as the transfer of rock and soil downslope by direct action of gravity without a flowing medium (such as water or ice). Mass Movement are: Creep Rock fall Slump Landslides Avalanches
Gravity Erosion
Section Assessment
Soils
Soils Soil is the loose covering of broken rock par3cles and decaying organic ma7er Soil is the end result of physical and chemical weathering. Soil forms as rock is broken down be weathering and mixes with other material on the surface. The longer a soil has been forming, the thicker it is. Climate has a great affect on soil forma3on. Temperature and precipita3on play an important role.
How is soil created? Decaying organic ma7er is called humus. It is ocen leaf li7er that is broken down by decomposers. Ex. Are ants, worms, etc.
Soil Formation During its development, soil forms in layers ver3cally. Solid bedrock from which weathered pieces of rock first break off is known as the parent rock. The weathered material then rests on top of the parent rock.
Residual vs. Transported Residual soil is soil that comes from the bedrock that it sits upon. A transported soil is soil that has been moved from a different loca3on
Soil Pro:ile A soil profile is a ver3cal sequence of soil layers. A dis3nct layer is called a soil horizon The three major layers are: A, B, C
Soil Horizons A Horizon- Topsoil- Soil rich in humus and usually dark colored B Horizon- Subsoil- Rich in clay minerals C Horizon- Weathered bedrock (parent rock).
Texture Size of soil par3cles is soil texture. Par3cles are classified according to size. In order from largest to smallest they are: Gravel Sand is the largest.05-2 mm Silt is the middle.0002 -.05 mm Clay is smallest >.002 mm
Fertility and Color Soil Fer8lity is the measure of how well a soil can support plant growth. A soils composi3on and climate are main factors in determining its color. Red/Yellow= Fe oxida3on Dark Colored= Humus Gray/Blue= low O2
Loam A loam is a soil that is equal parts of clay, sand and silt. It is the best for growing plants!
Soil Types Climac3c condi3ons are the main influences on soil development. Polar Soil Temperate Soil Desert Soil Tropical Soil