Chapter 14 Weathering and Erosion

1. Chapter 14Weathering and Erosion Ms. Hanlin Earth Science

2. Natural Arches • Landscape Arch is the longest natural arch in Arches National Park, Utah and may be the longest natural arch in the world. Like all natural arches, Landscape Arch was formed by the processes of weathering and erosion. • https://www.youtube.com/watch?v=4B36Lr0Unp4

3. So…How does this happen? • Mechanical weathering? • Wind, water, gravity, humans? • Chemical Weathering? • Oxidation, hydrolysis, carbonation, acid rain? • Rock Composition? • Climate? • Surface Area? • Elevation?

4. Weathering Processes • https://www.youtube.com/watch?v=2311yO5opVk • Fill in your guided notes (will be checked for participation points this week) • Most rocks are formed from the rock cycle. They can be formed into igneous, metamorphic, or sedimentary rocks. • When they are uplifted to the surface, they are exposed to lower temperature, lower pressure, gasses, water and living things. • All of these environmental factors lead to weathering and erosion.

5. Mechanical Weathering • Rock is broken down into smaller pieces by physical means. • The composition of the rock does not change, only the physical size and shape. • This can be accomplished by plants, animals, gravity, running water and wind. • Also, decreasing the amount of pressure on underlying rocks can change the physical characteristics, such as expansion.

6. Types of Mechanical Weathering • 1. Ice wedging: water seeps into the cracks of rock and then can freeze. When water freezes, it expands and can cause the rock to fracture or break. • This commonly occurs at high altitudes and cold climates or in areas with varied temperatures (falling below and rising above freezing) • https://www.youtube.com/watch?v=_XnCTcjNpuc

7. Types of Mechanical Weathering • 2. Abrasion: The collision of rocks that results in breaking and weathering. • This can be caused by gravity, running water, ice and wind. • Wind and the natural arches: wind carries small particles of sand at particular elevations, leading to weathering of the rocks and forming arches.

8. Types of Mechanical Weathering • 3. Plant and Animal activity: Plants and animals are important agents of mechanical weathering. • Plants: Grow and the roots can create pressure, causing rocks to break. • Plants fit into cracks making the crack bigger • Digging, burrowing animals affect the rate of weathering. • Groundhogs, earthworms, ants, etc.

9. Chemical Weathering • Definition: The process by which rock is broken down by chemical interactions with the environment. • Acts on the minerals in the rocks (rocks are a collection of different minerals) • Chemical reactions happen mainly between acid/base reactions.

10. Types of Chemical Weathering • 1. Oxidation: When elements combine with oxygen, the color red can appear on rocks, created by the formation of rust. • Mainly rocks with iron in composition. • 2. Hydrolysis: The change of the composition of minerals when they react with water. • Minerals often dissolve in the water and are carried to lower layers of rocks. • Process called leaching, leads to ore deposits such as aluminum and bauxite.

11. Types of Chemical Weathering • 3. Carbonation: When carbon dioxide from the air (think of the carbon cycle) dissolves in water, carbonic acid is formed. • Speeds up the process of hydrolysis, also can form minerals called carbonates, through carbonation. • 4. Organic Acids: Acids can be produced naturally by living things, such as lichens and mosses, leading to erosion and cracks in the rocks.

12. Types of Chemical Weathering • 5. Acid Precipitation: Natural rain water is naturally acidic because it combines with carbon dioxide in the air. When fossil fuels are burned in high concentrations, it can lead to acid precipitation. • This can lead to the erosion of many rocks, including national monuments.

13. Chapter 14: Section 1 and 2 • Homework: Due Wednesday • Read Chapter 14 and complete the end of reading questions for section 1 and section 2. • Vocabulary quiz Next Tuesday (assessment grade) • Notes over Section 2: Tomorrow • Start lab station activity

14. Section 2: Rates of Weathering • The Processes of mechanical and chemical weathering work very slowly. • Carbonation dissolves limestone at an average rate of only 1/20th of a centimeter every 100 years. • Many factors that factor into the rate of weathering. • 1. Rock Composition: The composition of the rock affects the rate of weathering. • Quartz resistant to chemical weathering • Limestone contains calcite, which weather rapidly from carbonation. • How strong the grains of rock are held together affect weathering rate.

15. Rate of Weathering • 2. Amount of Exposure: The greater the exposure to weathering agents, the greater the amount of weathering. • The amount of time rock is exposed is a factor • The surface area of the rock • Increase in SA increase in weathering • Natural fractures and joints increase surface area

16. Rate of Weathering • 3. Climate can have an effect on the rate of weathering. • Ice wedging caused from water freezing in the cracks of rocks • When temperatures rise, the rate of the chemical reactions accelerate. • Moisture can also increase chemical reaction rate. • Hot/dry climates have the slowest rates of weathering (mainly from lack of water)

17. Rate of Weathering • 4. Topography and Elevation: the elevation and the slope of the surface can influence weathering. • Colder climates at high elevations lead to ice wedging. • Rocks fall due to gravity on steep slopes. • 5. Plant, Animal, and Human Interactions • Mining and construction and human activity can expose rock at the surface, increasing reaction rate. • Chemical products of animals can speed up chemical weathering processes.