1. What is Weathering? Weathering is a set of physical, chemical, and biological processes that change the physical and chemical properties of rocks and soil at or near the earth's surface.

2. More about Weathering Weathering is the breakdown of rock to form sediment [very small pieces of rock]Weathering is the breakdown of rock to form sediment [very small pieces of rock] –Weathering happens to rocks that are NOT MOVING –Weathering is part of the Rock Cycle

3. There are three types of Weathering Mechanical [also called physical]Mechanical [also called physical] ChemicalChemical BiologicalBiological

4. Mechanical weathering breaks rocks down into smaller pieces, but does not change the composition of the rock. Types of mechanical weathering include: Frost wedging Exfoliation Thermal expansion Abrasion

5. In mechanical weathering, a rock is broken down into smaller pieces without changing its mineral composition.

6. Types of Mechanical Weathering Frost wedging – rocks break downFrost wedging – rocks break down when ice in cracks expands. Shattered when ice in cracks expands. Shattered rocks are common in cold climates rocks are common in cold climates where repeated freeze-thaw cycles where repeated freeze-thaw cycles gradually pry rocks apart. This type of gradually pry rocks apart. This type of weathering also causes pot holes. weathering also causes pot holes. Exfoliation - rock breaks off intoExfoliation - rock breaks off into sheets or layers that are parallel sheets or layers that are parallel to the earth’s surface to the earth’s surface

7. Enchanted rock is a huge example of exfoliation mechanical weathering close to home.

8. Thermal expansion and contraction extreme heating and cooling of rock can shatter rocks extreme heating and cooling of rock can shatter rocks Abrasion - wind, waves, rain, glaciers, abrade the rocks’ surfaces, wearing them down Types of Mechanical Weathering

9. Chemical weathering breaks rocks down chemically adding or removing chemical elements, and changes them into other materials. Chemical weathering consists of chemical reactions, most of which involve water.

10. Chemical Weathering Rock is broken down by chemical reactions that change its mineral composition and physical and chemical properties. Rocks are broken down by chemical actions (O 2, H 2 O, CO 2 ). It is the transformation or decomposition of one mineral into another. Water is most often a part of chemical weathering.

11. Chemical weathering happens when the minerals that make up a rock are changed, leading to the disintegration of the rock.

12. Chemical Weathering A stalagmite rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. Stalactites are formed by the deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions. Limestone is calcium carbonate rock which is dissolved by water that contains carbon dioxide forming a calcium bicarbonate.

13. Acid Rain Compounds from burning coal, oil and gas react chemically with water forming acids. Acid rain causes very rapid chemical weathering

14. Not all minerals are prone to chemical weathering. For example feldspar and quartz, common minerals in the rock granite, have very different levels of resistance to chemical weathering. Quartz doesn’t weather very easily, but feldspar does. Over a long time, it chemically changes into clay minerals.

15. Feldspar to clay + H 2 CO 3 (carbonic acid)

16. Karst Topography A type of landscape in rainy regions where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams. Created by chemical weathering of limestone.

17. A Karst landform is a feature created on the Earth's surface by the drainage of water into the ground or by its discharge at springs. The term derives from Kras, a region in western Slovenia where typical karst forms such as sinkholes, caves, natural bridges and sinking streams were first studied in detail. Karst Landforms

18. Physical and chemical weathering occur together. Physical weathering breaks rocks into pieces so more surface is exposed to chemical weathering which breaks it down further.

19. Biological Weathering can be both chemical and mechanical in nature.

20. Biological Weathering Biological weathering is the breakdown of rock caused by the action of living organisms, including plants, burrowing animals, and lichens. Biological weathering can be considered special types of mechanical or chemical weathering.Biological weathering can be considered special types of mechanical or chemical weathering.

21. Biological Weathering 1. Rocks can break because of animal burrowing. 2. Tree roots grow into cracks and widen them, which helps physical weathering. Roots also produce acids to help break down rock. 3. Bacteria, lichens and other organisms secrete acidic solutions, which helps chemical weathering. Biological Weathering 1. Rocks can break because of animal burrowing. 2. Tree roots grow into cracks and widen them, which helps physical weathering. Roots also produce acids to help break down rock. 3. Bacteria, lichens and other organisms secrete acidic solutions, which helps chemical weathering.

22. Living Organisms A lichen is a combination of fungus and algae, living together in a symbiotic relationship. Lichens can live on bare rock, and they break down rocks by secreting acids and other chemicals. Lichens that grow on rocks produce weak acids that chemically weather rock.

23. Biological Weathering

24. Weathering Rates Chemical weathering happens quickly in warm, moistChemical weathering happens quickly in warm, moist environments because water is needed for the environments because water is needed for the chemical reactions. chemical reactions. The warm weather speeds up the reactions. The more waterThe warm weather speeds up the reactions. The more water means there will be more weathering. means there will be more weathering. Surface area exposure: more surface area = greaterSurface area exposure: more surface area = greater weathering weathering

25. Weathering Rates Climate-dictates the temperature and amount of moistureClimate-dictates the temperature and amount of moisture #1 factor in weathering process#1 factor in weathering process Mineral composition-the harder the rock, the slower the rate of weathering, composition dictates resistance to weatheringMineral composition-the harder the rock, the slower the rate of weathering, composition dictates resistance to weathering