1. Weathering Chapter 7: Section 1

2. I. Weathering Weathering and It’s Effects Surface processes that work to break down rock are called weathering. Weathering breaks down rocks into smaller and smaller pieces. Two forms of weathering Mechanical (with some biological) Chemical (with some biological) Weathering can reduce mountains to hills and boulders to pebbles.

3. Mechanical Weathering The breakdown of rocks without changing their chemical composition. Fragments of parent rock formed without changing chemical composition. Fragments have exact characteristics as parent rock. Mechanical weathering is caused by many factors Tree roots, ice expanding, crystal growth, lightning, expansion and contraction, heating and cooling, friction, and wind erosion.

4. Plants and Animals (Mechanical Weathering) Roots grow into cracks in rocks. Start out thin as hair, then grow larger and larger. Act as a wedge forcing rock to crack into pieces. Example: Sidewalks buckling due to tree roots. Animals burrowing increases weathering of soil. Burrowing allows water and air to act on rock below the surface. Animals also bring un-weathered materials to the surface where weathering occurs.

7. Ice Wedging A natural process of breaking rocks down quickly. Process: Water seeps into the cracks of rocks/sidewalks Water expands as it freezes. Crack begins to widen. More water is able to seep in and freeze. Crack in rock widens even more. The process repeats until pieces break off the parent rock.

9. Wind Action Wind picks up dust particles. These particles act as abrasives, wearing away rock surfaces. Very similar to sand blasting.

10. II. Chemical Weathering Chemical Weathering is the process when water, air, or other chemicals wear away rocks and change their chemical composition. Water is called the universal solvent. Oxygen and hydrogen in water reacts with minerals. The minerals change into much different compounds. Example: Oxidation of Iron casues RUST

12. Acid (Chemical Weathering) Acids react with minerals, usually dissolving them over time. Acids form naturally in many ways. Carbonic Acid forms from carbon dioxide and water (very weak acid) and wears away limestone to make caves. Carbonic acid also wears away granite to make clay. Sulfuric Acid: formed when sulfur and water combines to form a strong acid that can wear away marble and concrete. Nitric Acid: (Strong Acid) produced by some plant roots and mosses; breaks down rocks and causes acid rain.

13. pH Scale The strength of acids and bases is measured by the pH scale. Scale goes from 0 (extremely acidic) to 14 (extremely basic or alkaline) 7 is neutral on the scale (water) Most minerals are more soluble in acidic soils than in neutral or slightly alkaline soils. Different plants grow better in different soil types. Peanuts grow better in soils with a 5.3 to 6.6 pH. Alfalfa grows best in soils having a pH of 6.2 to 7.8

14. Oxygen and Oxidation Oxidation is the bonding of oxygen to other elements that changes the chemical composition. Almost all elements oxidize. Iron  Iron Oxide (Rust) Aluminum  Aluminum Oxide white powder on window sills Sulfur  Sulfur Dioxide- Acid Rain Most comes from power plants. Copper Oxide – Turns copper green (Statue of Liberty)

16. III. Effects of Climate Climate plays a big part in how quickly mechanical and chemical weathering occur. Climate is the weather patterns for a given area over long periods of time. Mechanical and Chemical Weathering occur everywhere.

17. Cold Climate Weathering Freezing and thawing cycles allow ice wedging to break down rocks quickly. Warm/Wet Climate Weathering Chemical weathering acts more quickly and occurs more often. Dry Climate Weathering Wind action is the prevalent form of weathering.