WEATHERING

1. WEATHERING

2. WEATHERING • Nature of weathering and erosion • Weathering • chemical and/or physical breakdown of a rock or mineral material • weathering involves specific processes acting on materials at or near the Earth’s surface • Erosion • removal or transportation of material by agents as running water, glacial ice, wind, etc. • different degrees of weathering and erosion working together can form interesting geologic features as Bryce Canyon

3. Bryce Canyon National Park, Utah

4. WEATHERING • Kinds of weathering • Physical (Mechanical) • breakdown of a substance by disintegration • frost (ice) wedging • alternating freezing and thawing of moisture in rock openings causing rock disintegration • single most abundant form of physical weathering--potholes form from wedging • a slope of talus can form at base of a cliff or mountain as a mass wasting process

5. Frost wedging

6. Talus slope at the base of mountain

7. WEATHERING • unloading (exfoliation) • erosion of upper rock causes underlying rock to expand resulting in cracking and peeling of rock in slabs Half Dome in Yosemite National Park

8. WEATHERING • organic activity • burrowing worms or animals and roots of trees can cause rock disintegration

9. WEATHERING • Chemical weathering • breakdown of substance by decomposition resulting in formation of new minerals • water and acids especially carbonic acid are important agents • hydrolysis • chemical reaction between water and substance in which (OH) in water (HOH) becomes part of the new substance formed • often silicate minerals will weather by this process to form clay

10. WEATHERING • solution (leaching) • dissolving of substances by acids in water often leaving nonsolubilized remains • carbonate minerals are highly affected by leaching • oxidation • reaction of a substance with oxygen causing a rust material to form • manganese and especially iron minerals are affected by oxidation • often weathering of materials includes a combination of the 2 kinds of weathering

11. WEATHERING • Factors which affect the rate and/or extent of weathering • Total surface area of mineral or rock • chemical and physical weathering increases proportionately with amount of open space (cracks, holes, etc.) at surface and extending through the material • finer grained rocks weather greater than a coarser grained equivalent in composition and size • basalt and gabbro; rhyolite and granite

12. WEATHERING • Climate • temperature and amount of moisture can influence the kind and magnitude of weathering • in a humid hot climate there would be a lot of hydrolysis, leaching, oxidation and certain types of physical weathering but little or no frost wedging • in a dry cold climate there would be a sparce variety and lower magnitude of chemical weathering

13. WEATHERING • Cleopatra’s Needle was in Egypt for nearly 3500 years and shows minimal weathering compared to the same in New York for about 80 years in Egypt in New York

14. WEATHERING • Composition of rock or mineral substance • as mentioned earlier certain composition materials are affected by specific kinds of chemical weathering • Silicate mineral weathering series • based on composition alone silicate minerals higher in Bowen’s mineral series will decompose more than those lower in the series • a gabbro should weather at a greater rate and more extensively than a granite if all other weathering factors are the same

15. WEATHERING • which would weather faster and a greater rate, a basalt or a rhyolite if all other weathering factors are the same?

16. WEATHERING • Time • obviously time is a factor in all geologic processes including weathering rate and magnitude or extent of weathering • Soil • Definition and basic nature of soil • unconsolidated material formed from chemical and/or physical weathering of substances as bedrock or outcrops • contains at least some organic matter • can be in situ (in place) or transported • there is a classification of soil types

17. WEATHERING • Soil profile and soil horizons • typical soil profiles include 3 main horizons • 2 upper horizons, A and B are known as solum • A horizon is concentrated in organic matter and acids and represents an area of high leaching or solution activity • B horizon is concentrated in clay and rich in iron • eluviation is the removal of clay and solubilized materials from A horizon

18. WEATHERING • illuviation is the precipitation of eluviated materials in the B horizon • B horizon forms and thickens as the degree of eluviation and illuviation increase • C horizon • comprised of fragmented bedrock

19. A

20. WEATHERING • Soil creep • a form of mass wasting of earth materials • creep is often initiated if ground becomes saturated with water allowing gravity to pull the water logged soil downslope • freezing and thawing in soil can also cause heaving thus loosening the soil allowing creep Mass Wasting Examples Related to Soils

21. Soil Creep

22. Debris Slide

23. Rock and Debris Flow

24. Landslides in La Conchita, California

25. WEATHERING • Solifluction • a form of mass wasting and soil creep that occurs in regions underlain by perafrost in arctic climates • creep occurs in active layer above permafrost--active layer becomes saturated in water during summer months but not the impermeable permafrost layer--this results in a creep downslope of the active layer

26. WEATHERING Solifluction—diagram and picture