1. W EATHERING Weathering, Soil, and Erosion 2011-2012

2. W EATHERING D EFINITIONS Weathering – the breakup of rock due to exposure to processes that occur at Earth’s surface. Mechanical weathering Also called disintegration. Takes place when rock is split or broken into smaller pieces of the same material without changing its composition. Chemical weathering Also called decomposition. Takes place when the rock’s minerals are changed into different substances.

3. M ECHANICAL W EATHERING – I CE AND W ATER Water occupies 10% more space when it freezes  puts a lot of pressure on the container it’s in. Frost wedging – water freezes in the cracks in rocks and pushes the rock apart. Occurs in areas where the temperature varies from below freezing (0°C) to above freezing.

4. M ECHANICAL W EATHERING – I CE AND W ATER Repeated wetting and drying can break up rocks that contain clay (i.e. shale). Clay absorbs water easily and swells when wet. Clay shrinks as it dries. Repeated swelling and shrinking causes the rocks to break apart.

5. M ECHANICAL W EATHERING – A BRASION Rocks are moved by water, wind, and ice. Abrasion occurs when moving rocks grind and scrape against each other, wearing the rock materials away. The sand on the beach is a result of abrasion.

6. M ECHANICAL W EATHERING – P LANTS AND A NIMALS Plant roots can wedge into pores and crevices in rocks. As the roots grow larger, they push out on the rocks and cause them to split. Burrowing animals and insects dig holes in the soil, allowing air and water to reach bedrock and weather it.

7. M ECHANICAL W EATHERING – U PWARD E XPANSION Exfoliation – the peeling of surface layers from exposed bedrock. Example: Granite is lifted up and the rocks above it are worn away. The rocks form sheets and break off as seen in the photo. http://0.tqn.com/d/geology/1/0/H/L/exfoliation.jpg

8. C HEMICAL W EATHERING – W ATER Hydrolysis The chemical weathering by reaction of water with other substances. When some minerals are exposed to water, they dissolve into ions. These ions slowly react with the water and form clay minerals.

9. C HEMICAL W EATHERING – W ATER Carbonic acid Weak acid that is formed when carbon dioxide dissolves in rainwater. Seeps into the ground and reacts chemically with many common minerals. Example: Carbonic acid reacts with calcite, causing it to dissolve completely. This dissolving has formed underground caverns.

10. C HEMICAL W EATHERING – W ATER Acid rain Sulfur dioxide, nitrogen compounds, and carbon dioxide react with water in the air. Causes structures made of concrete, stone, and metal to wear out more quickly.

11. C HEMICAL W EATHERING – O XYGEN Oxidation The chemical reaction of oxygen with other substances. Very effective at weathering minerals that have iron in their chemical formulas. The formation of different types of rust (iron oxides).

12. R ATES OF W EATHERING – S URFACE E XPOSURE The rate at which a rock weathers is affected by the amount of surface that is exposed to chemical weathering processes. The more of a rock that is exposed, the faster it will weather.

13. R ATES OF W EATHERING – C OMPOSITION OF R OCK How fast or how slow a rock will weather depends on what it is made of. Rocks with layers of different compositions will wear at different rates.

14. R ATES OF W EATHERING – C LIMATE Wet climates are conducive to both chemical and mechanical weathering processes. Regions with cold or dry climates are more conducive to mechanical weathering.